FreeBSD/Linux Kernel Cross Reference
sys/fs/namei.c

     /*
      *  linux/fs/namei.c
      *
      *  Copyright (C) 1991, 1992  Linus Torvalds
      */
     
     /*
      * Some corrections by tytso.
      */
    
    /* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname
     * lookup logic.
     */
    /* [Feb-Apr 2000, AV] Rewrite to the new namespace architecture.
     */
    
    #include <linux/init.h>
    #include <linux/export.h>
    #include <linux/kernel.h>
    #include <linux/slab.h>
    #include <linux/fs.h>
    #include <linux/namei.h>
    #include <linux/pagemap.h>
    #include <linux/fsnotify.h>
    #include <linux/personality.h>
    #include <linux/security.h>
    #include <linux/ima.h>
    #include <linux/syscalls.h>
    #include <linux/mount.h>
    #include <linux/audit.h>
    #include <linux/capability.h>
    #include <linux/file.h>
    #include <linux/fcntl.h>
    #include <linux/device_cgroup.h>
    #include <linux/fs_struct.h>
    #include <linux/posix_acl.h>
    #include <asm/uaccess.h>
    
    #include "internal.h"
    #include "mount.h"
    
    /* [Feb-1997 T. Schoebel-Theuer]
     * Fundamental changes in the pathname lookup mechanisms (namei)
     * were necessary because of omirr.  The reason is that omirr needs
     * to know the _real_ pathname, not the user-supplied one, in case
     * of symlinks (and also when transname replacements occur).
     *
     * The new code replaces the old recursive symlink resolution with
     * an iterative one (in case of non-nested symlink chains).  It does
     * this with calls to <fs>_follow_link().
     * As a side effect, dir_namei(), _namei() and follow_link() are now 
     * replaced with a single function lookup_dentry() that can handle all 
     * the special cases of the former code.
     *
     * With the new dcache, the pathname is stored at each inode, at least as
     * long as the refcount of the inode is positive.  As a side effect, the
     * size of the dcache depends on the inode cache and thus is dynamic.
     *
     * [29-Apr-1998 C. Scott Ananian] Updated above description of symlink
     * resolution to correspond with current state of the code.
     *
     * Note that the symlink resolution is not *completely* iterative.
     * There is still a significant amount of tail- and mid- recursion in
     * the algorithm.  Also, note that <fs>_readlink() is not used in
     * lookup_dentry(): lookup_dentry() on the result of <fs>_readlink()
     * may return different results than <fs>_follow_link().  Many virtual
     * filesystems (including /proc) exhibit this behavior.
     */
    
    /* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation:
     * New symlink semantics: when open() is called with flags O_CREAT | O_EXCL
     * and the name already exists in form of a symlink, try to create the new
     * name indicated by the symlink. The old code always complained that the
     * name already exists, due to not following the symlink even if its target
     * is nonexistent.  The new semantics affects also mknod() and link() when
     * the name is a symlink pointing to a non-existent name.
     *
     * I don't know which semantics is the right one, since I have no access
     * to standards. But I found by trial that HP-UX 9.0 has the full "new"
     * semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the
     * "old" one. Personally, I think the new semantics is much more logical.
     * Note that "ln old new" where "new" is a symlink pointing to a non-existing
     * file does succeed in both HP-UX and SunOs, but not in Solaris
     * and in the old Linux semantics.
     */
    
    /* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink
     * semantics.  See the comments in "open_namei" and "do_link" below.
     *
     * [10-Sep-98 Alan Modra] Another symlink change.
     */
    
    /* [Feb-Apr 2000 AV] Complete rewrite. Rules for symlinks:
     *      inside the path - always follow.
     *      in the last component in creation/removal/renaming - never follow.
     *      if LOOKUP_FOLLOW passed - follow.
     *      if the pathname has trailing slashes - follow.
     *      otherwise - don't follow.
     * (applied in that order).
    *
    * [Jun 2000 AV] Inconsistent behaviour of open() in case if flags==O_CREAT
    * restored for 2.4. This is the last surviving part of old 4.2BSD bug.
    * During the 2.4 we need to fix the userland stuff depending on it -
    * hopefully we will be able to get rid of that wart in 2.5. So far only
    * XEmacs seems to be relying on it...
    */
   /*
    * [Sep 2001 AV] Single-semaphore locking scheme (kudos to David Holland)
    * implemented.  Let's see if raised priority of ->s_vfs_rename_mutex gives
    * any extra contention...
    */
   
   /* In order to reduce some races, while at the same time doing additional
    * checking and hopefully speeding things up, we copy filenames to the
    * kernel data space before using them..
    *
    * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
    * PATH_MAX includes the nul terminator --RR.
    */
   void final_putname(struct filename *name)
   {
           if (name->separate) {
                   __putname(name->name);
                   kfree(name);
           } else {
                   __putname(name);
           }
   }
   
   #define EMBEDDED_NAME_MAX       (PATH_MAX - sizeof(struct filename))
   
   static struct filename *
   getname_flags(const char __user *filename, int flags, int *empty)
   {
           struct filename *result, *err;
           int len;
           long max;
           char *kname;
   
           result = audit_reusename(filename);
           if (result)
                   return result;
   
           result = __getname();
           if (unlikely(!result))
                   return ERR_PTR(-ENOMEM);
   
           /*
            * First, try to embed the struct filename inside the names_cache
            * allocation
            */
           kname = (char *)result + sizeof(*result);
           result->name = kname;
           result->separate = false;
           max = EMBEDDED_NAME_MAX;
   
   recopy:
           len = strncpy_from_user(kname, filename, max);
           if (unlikely(len < 0)) {
                   err = ERR_PTR(len);
                   goto error;
           }
   
           /*
            * Uh-oh. We have a name that's approaching PATH_MAX. Allocate a
            * separate struct filename so we can dedicate the entire
            * names_cache allocation for the pathname, and re-do the copy from
            * userland.
            */
           if (len == EMBEDDED_NAME_MAX && max == EMBEDDED_NAME_MAX) {
                   kname = (char *)result;
   
                   result = kzalloc(sizeof(*result), GFP_KERNEL);
                   if (!result) {
                           err = ERR_PTR(-ENOMEM);
                           result = (struct filename *)kname;
                           goto error;
                   }
                   result->name = kname;
                   result->separate = true;
                   max = PATH_MAX;
                   goto recopy;
           }
   
           /* The empty path is special. */
           if (unlikely(!len)) {
                   if (empty)
                           *empty = 1;
                   err = ERR_PTR(-ENOENT);
                   if (!(flags & LOOKUP_EMPTY))
                           goto error;
           }
   
           err = ERR_PTR(-ENAMETOOLONG);
           if (unlikely(len >= PATH_MAX))
                   goto error;
   
           result->uptr = filename;
           audit_getname(result);
           return result;
   
   error:
           final_putname(result);
           return err;
   }
   
   struct filename *
   getname(const char __user * filename)
   {
           return getname_flags(filename, 0, NULL);
   }
   EXPORT_SYMBOL(getname);
   
   #ifdef CONFIG_AUDITSYSCALL
   void putname(struct filename *name)
   {
           if (unlikely(!audit_dummy_context()))
                   return audit_putname(name);
           final_putname(name);
   }
   #endif
   
   static int check_acl(struct inode *inode, int mask)
   {
   #ifdef CONFIG_FS_POSIX_ACL
           struct posix_acl *acl;
   
           if (mask & MAY_NOT_BLOCK) {
                   acl = get_cached_acl_rcu(inode, ACL_TYPE_ACCESS);
                   if (!acl)
                           return -EAGAIN;
                   /* no ->get_acl() calls in RCU mode... */
                   if (acl == ACL_NOT_CACHED)
                           return -ECHILD;
                   return posix_acl_permission(inode, acl, mask & ~MAY_NOT_BLOCK);
           }
   
           acl = get_cached_acl(inode, ACL_TYPE_ACCESS);
   
           /*
            * A filesystem can force a ACL callback by just never filling the
            * ACL cache. But normally you'd fill the cache either at inode
            * instantiation time, or on the first ->get_acl call.
            *
            * If the filesystem doesn't have a get_acl() function at all, we'll
            * just create the negative cache entry.
            */
           if (acl == ACL_NOT_CACHED) {
                   if (inode->i_op->get_acl) {
                           acl = inode->i_op->get_acl(inode, ACL_TYPE_ACCESS);
                           if (IS_ERR(acl))
                                   return PTR_ERR(acl);
                   } else {
                           set_cached_acl(inode, ACL_TYPE_ACCESS, NULL);
                           return -EAGAIN;
                   }
           }
   
           if (acl) {
                   int error = posix_acl_permission(inode, acl, mask);
                   posix_acl_release(acl);
                   return error;
           }
   #endif
   
           return -EAGAIN;
   }
   
   /*
    * This does the basic permission checking
    */
   static int acl_permission_check(struct inode *inode, int mask)
   {
           unsigned int mode = inode->i_mode;
   
           if (likely(uid_eq(current_fsuid(), inode->i_uid)))
                   mode >>= 6;
           else {
                   if (IS_POSIXACL(inode) && (mode & S_IRWXG)) {
                           int error = check_acl(inode, mask);
                           if (error != -EAGAIN)
                                   return error;
                   }
   
                   if (in_group_p(inode->i_gid))
                           mode >>= 3;
           }
   
           /*
            * If the DACs are ok we don't need any capability check.
            */
           if ((mask & ~mode & (MAY_READ | MAY_WRITE | MAY_EXEC)) == 0)
                   return 0;
           return -EACCES;
   }
   
   /**
    * generic_permission -  check for access rights on a Posix-like filesystem
    * @inode:      inode to check access rights for
    * @mask:       right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC, ...)
    *
    * Used to check for read/write/execute permissions on a file.
    * We use "fsuid" for this, letting us set arbitrary permissions
    * for filesystem access without changing the "normal" uids which
    * are used for other things.
    *
    * generic_permission is rcu-walk aware. It returns -ECHILD in case an rcu-walk
    * request cannot be satisfied (eg. requires blocking or too much complexity).
    * It would then be called again in ref-walk mode.
    */
   int generic_permission(struct inode *inode, int mask)
   {
           int ret;
   
           /*
            * Do the basic permission checks.
            */
           ret = acl_permission_check(inode, mask);
           if (ret != -EACCES)
                   return ret;
   
           if (S_ISDIR(inode->i_mode)) {
                   /* DACs are overridable for directories */
                   if (inode_capable(inode, CAP_DAC_OVERRIDE))
                           return 0;
                   if (!(mask & MAY_WRITE))
                           if (inode_capable(inode, CAP_DAC_READ_SEARCH))
                                   return 0;
                   return -EACCES;
           }
           /*
            * Read/write DACs are always overridable.
            * Executable DACs are overridable when there is
            * at least one exec bit set.
            */
           if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO))
                   if (inode_capable(inode, CAP_DAC_OVERRIDE))
                           return 0;
   
           /*
            * Searching includes executable on directories, else just read.
            */
           mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
           if (mask == MAY_READ)
                   if (inode_capable(inode, CAP_DAC_READ_SEARCH))
                           return 0;
   
           return -EACCES;
   }
   
   /*
    * We _really_ want to just do "generic_permission()" without
    * even looking at the inode->i_op values. So we keep a cache
    * flag in inode->i_opflags, that says "this has not special
    * permission function, use the fast case".
    */
   static inline int do_inode_permission(struct inode *inode, int mask)
   {
           if (unlikely(!(inode->i_opflags & IOP_FASTPERM))) {
                   if (likely(inode->i_op->permission))
                           return inode->i_op->permission(inode, mask);
   
                   /* This gets set once for the inode lifetime */
                   spin_lock(&inode->i_lock);
                   inode->i_opflags |= IOP_FASTPERM;
                   spin_unlock(&inode->i_lock);
           }
           return generic_permission(inode, mask);
   }
   
   /**
    * __inode_permission - Check for access rights to a given inode
    * @inode: Inode to check permission on
    * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
    *
    * Check for read/write/execute permissions on an inode.
    *
    * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
    *
    * This does not check for a read-only file system.  You probably want
    * inode_permission().
    */
   int __inode_permission(struct inode *inode, int mask)
   {
           int retval;
   
           if (unlikely(mask & MAY_WRITE)) {
                   /*
                    * Nobody gets write access to an immutable file.
                    */
                   if (IS_IMMUTABLE(inode))
                           return -EACCES;
           }
   
           retval = do_inode_permission(inode, mask);
           if (retval)
                   return retval;
   
           retval = devcgroup_inode_permission(inode, mask);
           if (retval)
                   return retval;
   
           return security_inode_permission(inode, mask);
   }
   
   /**
    * sb_permission - Check superblock-level permissions
    * @sb: Superblock of inode to check permission on
    * @inode: Inode to check permission on
    * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
    *
    * Separate out file-system wide checks from inode-specific permission checks.
    */
   static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
   {
           if (unlikely(mask & MAY_WRITE)) {
                   umode_t mode = inode->i_mode;
   
                   /* Nobody gets write access to a read-only fs. */
                   if ((sb->s_flags & MS_RDONLY) &&
                       (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
                           return -EROFS;
           }
           return 0;
   }
   
   /**
    * inode_permission - Check for access rights to a given inode
    * @inode: Inode to check permission on
    * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
    *
    * Check for read/write/execute permissions on an inode.  We use fs[ug]id for
    * this, letting us set arbitrary permissions for filesystem access without
    * changing the "normal" UIDs which are used for other things.
    *
    * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
    */
   int inode_permission(struct inode *inode, int mask)
   {
           int retval;
   
           retval = sb_permission(inode->i_sb, inode, mask);
           if (retval)
                   return retval;
           return __inode_permission(inode, mask);
   }
   
   /**
    * path_get - get a reference to a path
    * @path: path to get the reference to
    *
    * Given a path increment the reference count to the dentry and the vfsmount.
    */
   void path_get(struct path *path)
   {
           mntget(path->mnt);
           dget(path->dentry);
   }
   EXPORT_SYMBOL(path_get);
   
   /**
    * path_put - put a reference to a path
    * @path: path to put the reference to
    *
    * Given a path decrement the reference count to the dentry and the vfsmount.
    */
   void path_put(struct path *path)
   {
           dput(path->dentry);
           mntput(path->mnt);
   }
   EXPORT_SYMBOL(path_put);
   
   /*
    * Path walking has 2 modes, rcu-walk and ref-walk (see
    * Documentation/filesystems/path-lookup.txt).  In situations when we can't
    * continue in RCU mode, we attempt to drop out of rcu-walk mode and grab
    * normal reference counts on dentries and vfsmounts to transition to rcu-walk
    * mode.  Refcounts are grabbed at the last known good point before rcu-walk
    * got stuck, so ref-walk may continue from there. If this is not successful
    * (eg. a seqcount has changed), then failure is returned and it's up to caller
    * to restart the path walk from the beginning in ref-walk mode.
    */
   
   static inline void lock_rcu_walk(void)
   {
           br_read_lock(&vfsmount_lock);
           rcu_read_lock();
   }
   
   static inline void unlock_rcu_walk(void)
   {
           rcu_read_unlock();
           br_read_unlock(&vfsmount_lock);
   }
   
   /**
    * unlazy_walk - try to switch to ref-walk mode.
    * @nd: nameidata pathwalk data
    * @dentry: child of nd->path.dentry or NULL
    * Returns: 0 on success, -ECHILD on failure
    *
    * unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry
    * for ref-walk mode.  @dentry must be a path found by a do_lookup call on
    * @nd or NULL.  Must be called from rcu-walk context.
    */
   static int unlazy_walk(struct nameidata *nd, struct dentry *dentry)
   {
           struct fs_struct *fs = current->fs;
           struct dentry *parent = nd->path.dentry;
           int want_root = 0;
   
           BUG_ON(!(nd->flags & LOOKUP_RCU));
           if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
                   want_root = 1;
                   spin_lock(&fs->lock);
                   if (nd->root.mnt != fs->root.mnt ||
                                   nd->root.dentry != fs->root.dentry)
                           goto err_root;
           }
           spin_lock(&parent->d_lock);
           if (!dentry) {
                   if (!__d_rcu_to_refcount(parent, nd->seq))
                           goto err_parent;
                   BUG_ON(nd->inode != parent->d_inode);
           } else {
                   if (dentry->d_parent != parent)
                           goto err_parent;
                   spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
                   if (!__d_rcu_to_refcount(dentry, nd->seq))
                           goto err_child;
                   /*
                    * If the sequence check on the child dentry passed, then
                    * the child has not been removed from its parent. This
                    * means the parent dentry must be valid and able to take
                    * a reference at this point.
                    */
                   BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent);
                   BUG_ON(!parent->d_count);
                   parent->d_count++;
                   spin_unlock(&dentry->d_lock);
           }
           spin_unlock(&parent->d_lock);
           if (want_root) {
                   path_get(&nd->root);
                   spin_unlock(&fs->lock);
           }
           mntget(nd->path.mnt);
   
           unlock_rcu_walk();
           nd->flags &= ~LOOKUP_RCU;
           return 0;
   
   err_child:
           spin_unlock(&dentry->d_lock);
   err_parent:
           spin_unlock(&parent->d_lock);
   err_root:
           if (want_root)
                   spin_unlock(&fs->lock);
           return -ECHILD;
   }
   
   static inline int d_revalidate(struct dentry *dentry, unsigned int flags)
   {
           return dentry->d_op->d_revalidate(dentry, flags);
   }
   
   /**
    * complete_walk - successful completion of path walk
    * @nd:  pointer nameidata
    *
    * If we had been in RCU mode, drop out of it and legitimize nd->path.
    * Revalidate the final result, unless we'd already done that during
    * the path walk or the filesystem doesn't ask for it.  Return 0 on
    * success, -error on failure.  In case of failure caller does not
    * need to drop nd->path.
    */
   static int complete_walk(struct nameidata *nd)
   {
           struct dentry *dentry = nd->path.dentry;
           int status;
   
           if (nd->flags & LOOKUP_RCU) {
                   nd->flags &= ~LOOKUP_RCU;
                   if (!(nd->flags & LOOKUP_ROOT))
                           nd->root.mnt = NULL;
                   spin_lock(&dentry->d_lock);
                   if (unlikely(!__d_rcu_to_refcount(dentry, nd->seq))) {
                           spin_unlock(&dentry->d_lock);
                           unlock_rcu_walk();
                           return -ECHILD;
                   }
                   BUG_ON(nd->inode != dentry->d_inode);
                   spin_unlock(&dentry->d_lock);
                   mntget(nd->path.mnt);
                   unlock_rcu_walk();
           }
   
           if (likely(!(nd->flags & LOOKUP_JUMPED)))
                   return 0;
   
           if (likely(!(dentry->d_flags & DCACHE_OP_REVALIDATE)))
                   return 0;
   
           if (likely(!(dentry->d_sb->s_type->fs_flags & FS_REVAL_DOT)))
                   return 0;
   
           /* Note: we do not d_invalidate() */
           status = d_revalidate(dentry, nd->flags);
           if (status > 0)
                   return 0;
   
           if (!status)
                   status = -ESTALE;
   
           path_put(&nd->path);
           return status;
   }
   
   static __always_inline void set_root(struct nameidata *nd)
   {
           if (!nd->root.mnt)
                   get_fs_root(current->fs, &nd->root);
   }
   
   static int link_path_walk(const char *, struct nameidata *);
   
   static __always_inline void set_root_rcu(struct nameidata *nd)
   {
           if (!nd->root.mnt) {
                   struct fs_struct *fs = current->fs;
                   unsigned seq;
   
                   do {
                           seq = read_seqcount_begin(&fs->seq);
                           nd->root = fs->root;
                           nd->seq = __read_seqcount_begin(&nd->root.dentry->d_seq);
                   } while (read_seqcount_retry(&fs->seq, seq));
           }
   }
   
   static __always_inline int __vfs_follow_link(struct nameidata *nd, const char *link)
   {
           int ret;
   
           if (IS_ERR(link))
                   goto fail;
   
           if (*link == '/') {
                   set_root(nd);
                   path_put(&nd->path);
                   nd->path = nd->root;
                   path_get(&nd->root);
                   nd->flags |= LOOKUP_JUMPED;
           }
           nd->inode = nd->path.dentry->d_inode;
   
           ret = link_path_walk(link, nd);
           return ret;
   fail:
           path_put(&nd->path);
           return PTR_ERR(link);
   }
   
   static void path_put_conditional(struct path *path, struct nameidata *nd)
   {
           dput(path->dentry);
           if (path->mnt != nd->path.mnt)
                   mntput(path->mnt);
   }
   
   static inline void path_to_nameidata(const struct path *path,
                                           struct nameidata *nd)
   {
           if (!(nd->flags & LOOKUP_RCU)) {
                   dput(nd->path.dentry);
                   if (nd->path.mnt != path->mnt)
                           mntput(nd->path.mnt);
           }
           nd->path.mnt = path->mnt;
           nd->path.dentry = path->dentry;
   }
   
   /*
    * Helper to directly jump to a known parsed path from ->follow_link,
    * caller must have taken a reference to path beforehand.
    */
   void nd_jump_link(struct nameidata *nd, struct path *path)
   {
           path_put(&nd->path);
   
           nd->path = *path;
           nd->inode = nd->path.dentry->d_inode;
           nd->flags |= LOOKUP_JUMPED;
   
           BUG_ON(nd->inode->i_op->follow_link);
   }
   
   static inline void put_link(struct nameidata *nd, struct path *link, void *cookie)
   {
           struct inode *inode = link->dentry->d_inode;
           if (inode->i_op->put_link)
                   inode->i_op->put_link(link->dentry, nd, cookie);
           path_put(link);
   }
   
   int sysctl_protected_symlinks __read_mostly = 0;
   int sysctl_protected_hardlinks __read_mostly = 0;
   
   /**
    * may_follow_link - Check symlink following for unsafe situations
    * @link: The path of the symlink
    * @nd: nameidata pathwalk data
    *
    * In the case of the sysctl_protected_symlinks sysctl being enabled,
    * CAP_DAC_OVERRIDE needs to be specifically ignored if the symlink is
    * in a sticky world-writable directory. This is to protect privileged
    * processes from failing races against path names that may change out
    * from under them by way of other users creating malicious symlinks.
    * It will permit symlinks to be followed only when outside a sticky
    * world-writable directory, or when the uid of the symlink and follower
    * match, or when the directory owner matches the symlink's owner.
    *
    * Returns 0 if following the symlink is allowed, -ve on error.
    */
   static inline int may_follow_link(struct path *link, struct nameidata *nd)
   {
           const struct inode *inode;
           const struct inode *parent;
   
           if (!sysctl_protected_symlinks)
                   return 0;
   
           /* Allowed if owner and follower match. */
           inode = link->dentry->d_inode;
           if (uid_eq(current_cred()->fsuid, inode->i_uid))
                   return 0;
   
           /* Allowed if parent directory not sticky and world-writable. */
           parent = nd->path.dentry->d_inode;
           if ((parent->i_mode & (S_ISVTX|S_IWOTH)) != (S_ISVTX|S_IWOTH))
                   return 0;
   
           /* Allowed if parent directory and link owner match. */
           if (uid_eq(parent->i_uid, inode->i_uid))
                   return 0;
   
           audit_log_link_denied("follow_link", link);
           path_put_conditional(link, nd);
           path_put(&nd->path);
           return -EACCES;
   }
   
   /**
    * safe_hardlink_source - Check for safe hardlink conditions
    * @inode: the source inode to hardlink from
    *
    * Return false if at least one of the following conditions:
    *    - inode is not a regular file
    *    - inode is setuid
    *    - inode is setgid and group-exec
    *    - access failure for read and write
    *
    * Otherwise returns true.
    */
   static bool safe_hardlink_source(struct inode *inode)
   {
           umode_t mode = inode->i_mode;
   
           /* Special files should not get pinned to the filesystem. */
           if (!S_ISREG(mode))
                   return false;
   
           /* Setuid files should not get pinned to the filesystem. */
           if (mode & S_ISUID)
                   return false;
   
           /* Executable setgid files should not get pinned to the filesystem. */
           if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP))
                   return false;
   
           /* Hardlinking to unreadable or unwritable sources is dangerous. */
           if (inode_permission(inode, MAY_READ | MAY_WRITE))
                   return false;
   
           return true;
   }
   
   /**
    * may_linkat - Check permissions for creating a hardlink
    * @link: the source to hardlink from
    *
    * Block hardlink when all of:
    *  - sysctl_protected_hardlinks enabled
    *  - fsuid does not match inode
    *  - hardlink source is unsafe (see safe_hardlink_source() above)
    *  - not CAP_FOWNER
    *
    * Returns 0 if successful, -ve on error.
    */
   static int may_linkat(struct path *link)
   {
           const struct cred *cred;
           struct inode *inode;
   
           if (!sysctl_protected_hardlinks)
                   return 0;
   
           cred = current_cred();
           inode = link->dentry->d_inode;
   
           /* Source inode owner (or CAP_FOWNER) can hardlink all they like,
            * otherwise, it must be a safe source.
            */
           if (uid_eq(cred->fsuid, inode->i_uid) || safe_hardlink_source(inode) ||
               capable(CAP_FOWNER))
                   return 0;
   
           audit_log_link_denied("linkat", link);
           return -EPERM;
   }
   
   static __always_inline int
   follow_link(struct path *link, struct nameidata *nd, void **p)
   {
           struct dentry *dentry = link->dentry;
           int error;
           char *s;
   
           BUG_ON(nd->flags & LOOKUP_RCU);
   
           if (link->mnt == nd->path.mnt)
                   mntget(link->mnt);
   
           error = -ELOOP;
           if (unlikely(current->total_link_count >= 40))
                   goto out_put_nd_path;
   
           cond_resched();
           current->total_link_count++;
   
           touch_atime(link);
           nd_set_link(nd, NULL);
   
           error = security_inode_follow_link(link->dentry, nd);
           if (error)
                   goto out_put_nd_path;
   
           nd->last_type = LAST_BIND;
           *p = dentry->d_inode->i_op->follow_link(dentry, nd);
           error = PTR_ERR(*p);
           if (IS_ERR(*p))
                   goto out_put_nd_path;
   
           error = 0;
           s = nd_get_link(nd);
           if (s) {
                   error = __vfs_follow_link(nd, s);
                   if (unlikely(error))
                           put_link(nd, link, *p);
           }
   
           return error;
   
   out_put_nd_path:
           *p = NULL;
           path_put(&nd->path);
           path_put(link);
           return error;
   }
   
   static int follow_up_rcu(struct path *path)
   {
           struct mount *mnt = real_mount(path->mnt);
           struct mount *parent;
           struct dentry *mountpoint;
   
           parent = mnt->mnt_parent;
           if (&parent->mnt == path->mnt)
                   return 0;
           mountpoint = mnt->mnt_mountpoint;
           path->dentry = mountpoint;
           path->mnt = &parent->mnt;
           return 1;
   }
   
   /*
    * follow_up - Find the mountpoint of path's vfsmount
    *
    * Given a path, find the mountpoint of its source file system.
    * Replace @path with the path of the mountpoint in the parent mount.
    * Up is towards /.
    *
    * Return 1 if we went up a level and 0 if we were already at the
    * root.
    */
   int follow_up(struct path *path)
   {
           struct mount *mnt = real_mount(path->mnt);
           struct mount *parent;
           struct dentry *mountpoint;
   
           br_read_lock(&vfsmount_lock);
           parent = mnt->mnt_parent;
           if (parent == mnt) {
                   br_read_unlock(&vfsmount_lock);
                   return 0;
           }
           mntget(&parent->mnt);
           mountpoint = dget(mnt->mnt_mountpoint);
           br_read_unlock(&vfsmount_lock);
           dput(path->dentry);
           path->dentry = mountpoint;
           mntput(path->mnt);
           path->mnt = &parent->mnt;
           return 1;
   }
   
   /*
    * Perform an automount
    * - return -EISDIR to tell follow_managed() to stop and return the path we
    *   were called with.
    */
   static int follow_automount(struct path *path, unsigned flags,
                               bool *need_mntput)
   {
           struct vfsmount *mnt;
           int err;
   
           if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
                   return -EREMOTE;
   
           /* We don't want to mount if someone's just doing a stat -
            * unless they're stat'ing a directory and appended a '/' to
            * the name.
            *
            * We do, however, want to mount if someone wants to open or
            * create a file of any type under the mountpoint, wants to
            * traverse through the mountpoint or wants to open the
            * mounted directory.  Also, autofs may mark negative dentries
            * as being automount points.  These will need the attentions
            * of the daemon to instantiate them before they can be used.
            */
           if (!(flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
                        LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
               path->dentry->d_inode)
                   return -EISDIR;
   
           current->total_link_count++;
           if (current->total_link_count >= 40)
                   return -ELOOP;
   
           mnt = path->dentry->d_op->d_automount(path);
           if (IS_ERR(mnt)) {
                   /*
                    * The filesystem is allowed to return -EISDIR here to indicate
                    * it doesn't want to automount.  For instance, autofs would do
                    * this so that its userspace daemon can mount on this dentry.
                    *
                    * However, we can only permit this if it's a terminal point in
                    * the path being looked up; if it wasn't then the remainder of
                    * the path is inaccessible and we should say so.
                    */
                   if (PTR_ERR(mnt) == -EISDIR && (flags & LOOKUP_PARENT))
                           return -EREMOTE;
                   return PTR_ERR(mnt);
           }
   
           if (!mnt) /* mount collision */
                   return 0;
   
           if (!*need_mntput) {
                   /* lock_mount() may release path->mnt on error */
                   mntget(path->mnt);
                   *need_mntput = true;
           }
           err = finish_automount(mnt, path);
   
           switch (err) {
           case -EBUSY:
                   /* Someone else made a mount here whilst we were busy */
                   return 0;
           case 0:
                   path_put(path);
                   path->mnt = mnt;
                   path->dentry = dget(mnt->mnt_root);
                   return 0;
           default:
                   return err;
           }
   
   }
   
   /*
    * Handle a dentry that is managed in some way.
    * - Flagged for transit management (autofs)
    * - Flagged as mountpoint
    * - Flagged as automount point
   *
   * This may only be called in refwalk mode.
   *
   * Serialization is taken care of in namespace.c
   */
  static int follow_managed(struct path *path, unsigned flags)
  {
          struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */
          unsigned managed;
          bool need_mntput = false;
          int ret = 0;
  
          /* Given that we're not holding a lock here, we retain the value in a
           * local variable for each dentry as we look at it so that we don't see
           * the components of that value change under us */
          while (managed = ACCESS_ONCE(path->dentry->d_flags),
                 managed &= DCACHE_MANAGED_DENTRY,
                 unlikely(managed != 0)) {
                  /* Allow the filesystem to manage the transit without i_mutex
                   * being held. */
                  if (managed & DCACHE_MANAGE_TRANSIT) {
                          BUG_ON(!path->dentry->d_op);
                          BUG_ON(!path->dentry->d_op->d_manage);
                          ret = path->dentry->d_op->d_manage(path->dentry, false);
                          if (ret < 0)
                                  break;
                  }
  
                  /* Transit to a mounted filesystem. */
                  if (managed & DCACHE_MOUNTED) {
                          struct vfsmount *mounted = lookup_mnt(path);
                          if (mounted) {
                                  dput(path->dentry);
                                  if (need_mntput)
                                          mntput(path->mnt);
                                  path->mnt = mounted;
                                  path->dentry = dget(mounted->mnt_root);
                                  need_mntput = true;
                                  continue;
                          }
  
                          /* Something is mounted on this dentry in another
                           * namespace and/or whatever was mounted there in this
                           * namespace got unmounted before we managed to get the
                           * vfsmount_lock */
                  }
  
                  /* Handle an automount point */
                  if (managed & DCACHE_NEED_AUTOMOUNT) {
                          ret = follow_automount(path, flags, &need_mntput);
                          if (ret < 0)
                                  break;
                          continue;
                  }
  
                  /* We didn't change the current path point */
                  break;
          }
  
          if (need_mntput && path->mnt == mnt)
                  mntput(path->mnt);
          if (ret == -EISDIR)
                  ret = 0;
          return ret < 0 ? ret : need_mntput;
  }
  
  int follow_down_one(struct path *path)
  {
          struct vfsmount *mounted;
  
          mounted = lookup_mnt(path);
          if (mounted) {
                  dput(path->dentry);
                  mntput(path->mnt);
                  path->mnt = mounted;
                  path->dentry = dget(mounted->mnt_root);
                  return 1;
          }
          return 0;
  }
  
  static inline bool managed_dentry_might_block(struct dentry *dentry)
  {
          return (dentry->d_flags & DCACHE_MANAGE_TRANSIT &&
                  dentry->d_op->d_manage(dentry, true) < 0);
  }
  
  /*
   * Try to skip to top of mountpoint pile in rcuwalk mode.  Fail if
   * we meet a managed dentry that would need blocking.
   */
  static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
                                 struct inode **inode)
  {
          for (;;) {
                  struct mount *mounted;
                  /*
                   * Don't forget we might have a non-mountpoint managed dentry
                   * that wants to block transit.
                   */
                  if (unlikely(managed_dentry_might_block(path->dentry)))
                          return false;
  
                  if (!d_mountpoint(path->dentry))
                          break;
  
                  mounted = __lookup_mnt(path->mnt, path->dentry, 1);
                  if (!mounted)
                          break;
                  path->mnt = &mounted->mnt;
                  path->dentry = mounted->mnt.mnt_root;
                  nd->flags |= LOOKUP_JUMPED;
                  nd->seq = read_seqcount_begin(&path->dentry->d_seq);
                  /*
                   * Update the inode too. We don't need to re-check the
                   * dentry sequence number here after this d_inode read,
                   * because a mount-point is always pinned.
                   */
                  *inode = path->dentry->d_inode;
          }
          return true;
  }
  
  static void follow_mount_rcu(struct nameidata *nd)
  {
          while (d_mountpoint(nd->path.dentry)) {
                  struct mount *mounted;
                  mounted = __lookup_mnt(nd->path.mnt, nd->path.dentry, 1);
                  if (!mounted)
                          break;
                  nd->path.mnt = &mounted->mnt;
                  nd->path.dentry = mounted->mnt.mnt_root;
                  nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
          }
  }
  
  static int follow_dotdot_rcu(struct nameidata *nd)
  {
          set_root_rcu(nd);
  
          while (1) {
                  if (nd->path.dentry == nd->root.dentry &&
                      nd->path.mnt == nd->root.mnt) {
                          break;
                  }
                  if (nd->path.dentry != nd->path.mnt->mnt_root) {
                          struct dentry *old = nd->path.dentry;
                          struct dentry *parent = old->d_parent;
                          unsigned seq;
  
                          seq = read_seqcount_begin(&parent->d_seq);
                          if (read_seqcount_retry(&old->d_seq, nd->seq))
                                  goto failed;
                          nd->path.dentry = parent;
                          nd->seq = seq;
                          break;
                  }
                  if (!follow_up_rcu(&nd->path))
                          break;
                  nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
          }
          follow_mount_rcu(nd);
          nd->inode = nd->path.dentry->d_inode;
          return 0;
  
  failed:
          nd->flags &= ~LOOKUP_RCU;
          if (!(nd->flags & LOOKUP_ROOT))
                  nd->root.mnt = NULL;
          unlock_rcu_walk();
          return -ECHILD;
  }
  
  /*
   * Follow down to the covering mount currently visible to userspace.  At each
   * point, the filesystem owning that dentry may be queried as to whether the
   * caller is permitted to proceed or not.
   */
  int follow_down(struct path *path)
  {
          unsigned managed;
          int ret;
  
          while (managed = ACCESS_ONCE(path->dentry->d_flags),
                 unlikely(managed & DCACHE_MANAGED_DENTRY)) {
                  /* Allow the filesystem to manage the transit without i_mutex
                   * being held.
                   *
                   * We indicate to the filesystem if someone is trying to mount
                   * something here.  This gives autofs the chance to deny anyone
                   * other than its daemon the right to mount on its
                   * superstructure.
                   *
                   * The filesystem may sleep at this point.
                   */
                  if (managed & DCACHE_MANAGE_TRANSIT) {
                          BUG_ON(!path->dentry->d_op);
                          BUG_ON(!path->dentry->d_op->d_manage);
                          ret = path->dentry->d_op->d_manage(
                                  path->dentry, false);
                          if (ret < 0)
                                  return ret == -EISDIR ? 0 : ret;
                  }
  
                  /* Transit to a mounted filesystem. */
                  if (managed & DCACHE_MOUNTED) {
                          struct vfsmount *mounted = lookup_mnt(path);
                          if (!mounted)
                                  break;
                          dput(path->dentry);
                          mntput(path->mnt);
                          path->mnt = mounted;
                          path->dentry = dget(mounted->mnt_root);
                          continue;
                  }
  
                  /* Don't handle automount points here */
                  break;
          }
          return 0;
  }
  
  /*
   * Skip to top of mountpoint pile in refwalk mode for follow_dotdot()
   */
  static void follow_mount(struct path *path)
  {
          while (d_mountpoint(path->dentry)) {
                  struct vfsmount *mounted = lookup_mnt(path);
                  if (!mounted)
                          break;
                  dput(path->dentry);
                  mntput(path->mnt);
                  path->mnt = mounted;
                  path->dentry = dget(mounted->mnt_root);
          }
  }
  
  static void follow_dotdot(struct nameidata *nd)
  {
          set_root(nd);
  
          while(1) {
                  struct dentry *old = nd->path.dentry;
  
                  if (nd->path.dentry == nd->root.dentry &&
                      nd->path.mnt == nd->root.mnt) {
                          break;
                  }
                  if (nd->path.dentry != nd->path.mnt->mnt_root) {
                          /* rare case of legitimate dget_parent()... */
                          nd->path.dentry = dget_parent(nd->path.dentry);
                          dput(old);
                          break;
                  }
                  if (!follow_up(&nd->path))
                          break;
          }
          follow_mount(&nd->path);
          nd->inode = nd->path.dentry->d_inode;
  }
  
  /*
   * This looks up the name in dcache, possibly revalidates the old dentry and
   * allocates a new one if not found or not valid.  In the need_lookup argument
   * returns whether i_op->lookup is necessary.
   *
   * dir->d_inode->i_mutex must be held
   */
  static struct dentry *lookup_dcache(struct qstr *name, struct dentry *dir,
                                      unsigned int flags, bool *need_lookup)
  {
          struct dentry *dentry;
          int error;
  
          *need_lookup = false;
          dentry = d_lookup(dir, name);
          if (dentry) {
                  if (dentry->d_flags & DCACHE_OP_REVALIDATE) {
                          error = d_revalidate(dentry, flags);
                          if (unlikely(error <= 0)) {
                                  if (error < 0) {
                                          dput(dentry);
                                          return ERR_PTR(error);
                                  } else if (!d_invalidate(dentry)) {
                                          dput(dentry);
                                          dentry = NULL;
                                  }
                          }
                  }
          }
  
          if (!dentry) {
                  dentry = d_alloc(dir, name);
                  if (unlikely(!dentry))
                          return ERR_PTR(-ENOMEM);
  
                  *need_lookup = true;
          }
          return dentry;
  }
  
  /*
   * Call i_op->lookup on the dentry.  The dentry must be negative but may be
   * hashed if it was pouplated with DCACHE_NEED_LOOKUP.
   *
   * dir->d_inode->i_mutex must be held
   */
  static struct dentry *lookup_real(struct inode *dir, struct dentry *dentry,
                                    unsigned int flags)
  {
          struct dentry *old;
  
          /* Don't create child dentry for a dead directory. */
          if (unlikely(IS_DEADDIR(dir))) {
                  dput(dentry);
                  return ERR_PTR(-ENOENT);
          }
  
          old = dir->i_op->lookup(dir, dentry, flags);
          if (unlikely(old)) {
                  dput(dentry);
                  dentry = old;
          }
          return dentry;
  }
  
  static struct dentry *__lookup_hash(struct qstr *name,
                  struct dentry *base, unsigned int flags)
  {
          bool need_lookup;
          struct dentry *dentry;
  
          dentry = lookup_dcache(name, base, flags, &need_lookup);
          if (!need_lookup)
                  return dentry;
  
          return lookup_real(base->d_inode, dentry, flags);
  }
  
  /*
   *  It's more convoluted than I'd like it to be, but... it's still fairly
   *  small and for now I'd prefer to have fast path as straight as possible.
   *  It _is_ time-critical.
   */
  static int lookup_fast(struct nameidata *nd, struct qstr *name,
                         struct path *path, struct inode **inode)
  {
          struct vfsmount *mnt = nd->path.mnt;
          struct dentry *dentry, *parent = nd->path.dentry;
          int need_reval = 1;
          int status = 1;
          int err;
  
          /*
           * Rename seqlock is not required here because in the off chance
           * of a false negative due to a concurrent rename, we're going to
           * do the non-racy lookup, below.
           */
          if (nd->flags & LOOKUP_RCU) {
                  unsigned seq;
                  dentry = __d_lookup_rcu(parent, name, &seq, nd->inode);
                  if (!dentry)
                          goto unlazy;
  
                  /*
                   * This sequence count validates that the inode matches
                   * the dentry name information from lookup.
                   */
                  *inode = dentry->d_inode;
                  if (read_seqcount_retry(&dentry->d_seq, seq))
                          return -ECHILD;
  
                  /*
                   * This sequence count validates that the parent had no
                   * changes while we did the lookup of the dentry above.
                   *
                   * The memory barrier in read_seqcount_begin of child is
                   *  enough, we can use __read_seqcount_retry here.
                   */
                  if (__read_seqcount_retry(&parent->d_seq, nd->seq))
                          return -ECHILD;
                  nd->seq = seq;
  
                  if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) {
                          status = d_revalidate(dentry, nd->flags);
                          if (unlikely(status <= 0)) {
                                  if (status != -ECHILD)
                                          need_reval = 0;
                                  goto unlazy;
                          }
                  }
                  path->mnt = mnt;
                  path->dentry = dentry;
                  if (unlikely(!__follow_mount_rcu(nd, path, inode)))
                          goto unlazy;
                  if (unlikely(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT))
                          goto unlazy;
                  return 0;
  unlazy:
                  if (unlazy_walk(nd, dentry))
                          return -ECHILD;
          } else {
                  dentry = __d_lookup(parent, name);
          }
  
          if (unlikely(!dentry))
                  goto need_lookup;
  
          if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE) && need_reval)
                  status = d_revalidate(dentry, nd->flags);
          if (unlikely(status <= 0)) {
                  if (status < 0) {
                          dput(dentry);
                          return status;
                  }
                  if (!d_invalidate(dentry)) {
                          dput(dentry);
                          goto need_lookup;
                  }
          }
  
          path->mnt = mnt;
          path->dentry = dentry;
          err = follow_managed(path, nd->flags);
          if (unlikely(err < 0)) {
                  path_put_conditional(path, nd);
                  return err;
          }
          if (err)
                  nd->flags |= LOOKUP_JUMPED;
          *inode = path->dentry->d_inode;
          return 0;
  
  need_lookup:
          return 1;
  }
  
  /* Fast lookup failed, do it the slow way */
  static int lookup_slow(struct nameidata *nd, struct qstr *name,
                         struct path *path)
  {
          struct dentry *dentry, *parent;
          int err;
  
          parent = nd->path.dentry;
          BUG_ON(nd->inode != parent->d_inode);
  
          mutex_lock(&parent->d_inode->i_mutex);
          dentry = __lookup_hash(name, parent, nd->flags);
          mutex_unlock(&parent->d_inode->i_mutex);
          if (IS_ERR(dentry))
                  return PTR_ERR(dentry);
          path->mnt = nd->path.mnt;
          path->dentry = dentry;
          err = follow_managed(path, nd->flags);
          if (unlikely(err < 0)) {
                  path_put_conditional(path, nd);
                  return err;
          }
          if (err)
                  nd->flags |= LOOKUP_JUMPED;
          return 0;
  }
  
  static inline int may_lookup(struct nameidata *nd)
  {
          if (nd->flags & LOOKUP_RCU) {
                  int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK);
                  if (err != -ECHILD)
                          return err;
                  if (unlazy_walk(nd, NULL))
                          return -ECHILD;
          }
          return inode_permission(nd->inode, MAY_EXEC);
  }
  
  static inline int handle_dots(struct nameidata *nd, int type)
  {
          if (type == LAST_DOTDOT) {
                  if (nd->flags & LOOKUP_RCU) {
                          if (follow_dotdot_rcu(nd))
                                  return -ECHILD;
                  } else
                          follow_dotdot(nd);
          }
          return 0;
  }
  
  static void terminate_walk(struct nameidata *nd)
  {
          if (!(nd->flags & LOOKUP_RCU)) {
                  path_put(&nd->path);
          } else {
                  nd->flags &= ~LOOKUP_RCU;
                  if (!(nd->flags & LOOKUP_ROOT))
                          nd->root.mnt = NULL;
                  unlock_rcu_walk();
          }
  }
  
  /*
   * Do we need to follow links? We _really_ want to be able
   * to do this check without having to look at inode->i_op,
   * so we keep a cache of "no, this doesn't need follow_link"
   * for the common case.
   */
  static inline int should_follow_link(struct inode *inode, int follow)
  {
          if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
                  if (likely(inode->i_op->follow_link))
                          return follow;
  
                  /* This gets set once for the inode lifetime */
                  spin_lock(&inode->i_lock);
                  inode->i_opflags |= IOP_NOFOLLOW;
                  spin_unlock(&inode->i_lock);
          }
          return 0;
  }
  
  static inline int walk_component(struct nameidata *nd, struct path *path,
                  struct qstr *name, int type, int follow)
  {
          struct inode *inode;
          int err;
          /*
           * "." and ".." are special - ".." especially so because it has
           * to be able to know about the current root directory and
           * parent relationships.
           */
          if (unlikely(type != LAST_NORM))
                  return handle_dots(nd, type);
          err = lookup_fast(nd, name, path, &inode);
          if (unlikely(err)) {
                  if (err < 0)
                          goto out_err;
  
                  err = lookup_slow(nd, name, path);
                  if (err < 0)
                          goto out_err;
  
                  inode = path->dentry->d_inode;
          }
          err = -ENOENT;
          if (!inode)
                  goto out_path_put;
  
          if (should_follow_link(inode, follow)) {
                  if (nd->flags & LOOKUP_RCU) {
                          if (unlikely(unlazy_walk(nd, path->dentry))) {
                                  err = -ECHILD;
                                  goto out_err;
                          }
                  }
                  BUG_ON(inode != path->dentry->d_inode);
                  return 1;
          }
          path_to_nameidata(path, nd);
          nd->inode = inode;
          return 0;
  
  out_path_put:
          path_to_nameidata(path, nd);
  out_err:
          terminate_walk(nd);
          return err;
  }
  
  /*
   * This limits recursive symlink follows to 8, while
   * limiting consecutive symlinks to 40.
   *
   * Without that kind of total limit, nasty chains of consecutive
   * symlinks can cause almost arbitrarily long lookups.
   */
  static inline int nested_symlink(struct path *path, struct nameidata *nd)
  {
          int res;
  
          if (unlikely(current->link_count >= MAX_NESTED_LINKS)) {
                  path_put_conditional(path, nd);
                  path_put(&nd->path);
                  return -ELOOP;
          }
          BUG_ON(nd->depth >= MAX_NESTED_LINKS);
  
          nd->depth++;
          current->link_count++;
  
          do {
                  struct path link = *path;
                  void *cookie;
  
                  res = follow_link(&link, nd, &cookie);
                  if (res)
                          break;
                  res = walk_component(nd, path, &nd->last,
                                       nd->last_type, LOOKUP_FOLLOW);
                  put_link(nd, &link, cookie);
          } while (res > 0);
  
          current->link_count--;
          nd->depth--;
          return res;
  }
  
  /*
   * We really don't want to look at inode->i_op->lookup
   * when we don't have to. So we keep a cache bit in
   * the inode ->i_opflags field that says "yes, we can
   * do lookup on this inode".
   */
  static inline int can_lookup(struct inode *inode)
  {
          if (likely(inode->i_opflags & IOP_LOOKUP))
                  return 1;
          if (likely(!inode->i_op->lookup))
                  return 0;
  
          /* We do this once for the lifetime of the inode */
          spin_lock(&inode->i_lock);
          inode->i_opflags |= IOP_LOOKUP;
          spin_unlock(&inode->i_lock);
          return 1;
  }
  
  /*
   * We can do the critical dentry name comparison and hashing
   * operations one word at a time, but we are limited to:
   *
   * - Architectures with fast unaligned word accesses. We could
   *   do a "get_unaligned()" if this helps and is sufficiently
   *   fast.
   *
   * - Little-endian machines (so that we can generate the mask
   *   of low bytes efficiently). Again, we *could* do a byte
   *   swapping load on big-endian architectures if that is not
   *   expensive enough to make the optimization worthless.
   *
   * - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we
   *   do not trap on the (extremely unlikely) case of a page
   *   crossing operation.
   *
   * - Furthermore, we need an efficient 64-bit compile for the
   *   64-bit case in order to generate the "number of bytes in
   *   the final mask". Again, that could be replaced with a
   *   efficient population count instruction or similar.
   */
  #ifdef CONFIG_DCACHE_WORD_ACCESS
  
  #include <asm/word-at-a-time.h>
  
  #ifdef CONFIG_64BIT
  
  static inline unsigned int fold_hash(unsigned long hash)
  {
          hash += hash >> (8*sizeof(int));
          return hash;
  }
  
  #else   /* 32-bit case */
  
  #define fold_hash(x) (x)
  
  #endif
  
  unsigned int full_name_hash(const unsigned char *name, unsigned int len)
  {
          unsigned long a, mask;
          unsigned long hash = 0;
  
          for (;;) {
                  a = load_unaligned_zeropad(name);
                  if (len < sizeof(unsigned long))
                          break;
                  hash += a;
                  hash *= 9;
                  name += sizeof(unsigned long);
                  len -= sizeof(unsigned long);
                  if (!len)
                          goto done;
          }
          mask = ~(~0ul << len*8);
          hash += mask & a;
  done:
          return fold_hash(hash);
  }
  EXPORT_SYMBOL(full_name_hash);
  
  /*
   * Calculate the length and hash of the path component, and
   * return the length of the component;
   */
  static inline unsigned long hash_name(const char *name, unsigned int *hashp)
  {
          unsigned long a, b, adata, bdata, mask, hash, len;
          const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
  
          hash = a = 0;
          len = -sizeof(unsigned long);
          do {
                  hash = (hash + a) * 9;
                  len += sizeof(unsigned long);
                  a = load_unaligned_zeropad(name+len);
                  b = a ^ REPEAT_BYTE('/');
          } while (!(has_zero(a, &adata, &constants) | has_zero(b, &bdata, &constants)));
  
          adata = prep_zero_mask(a, adata, &constants);
          bdata = prep_zero_mask(b, bdata, &constants);
  
          mask = create_zero_mask(adata | bdata);
  
          hash += a & zero_bytemask(mask);
          *hashp = fold_hash(hash);
  
          return len + find_zero(mask);
  }
  
  #else
  
  unsigned int full_name_hash(const unsigned char *name, unsigned int len)
  {
          unsigned long hash = init_name_hash();
          while (len--)
                  hash = partial_name_hash(*name++, hash);
          return end_name_hash(hash);
  }
  EXPORT_SYMBOL(full_name_hash);
  
  /*
   * We know there's a real path component here of at least
   * one character.
   */
  static inline unsigned long hash_name(const char *name, unsigned int *hashp)
  {
          unsigned long hash = init_name_hash();
          unsigned long len = 0, c;
  
          c = (unsigned char)*name;
          do {
                  len++;
                  hash = partial_name_hash(c, hash);
                  c = (unsigned char)name[len];
          } while (c && c != '/');
          *hashp = end_name_hash(hash);
          return len;
  }
  
  #endif
  
  /*
   * Name resolution.
   * This is the basic name resolution function, turning a pathname into
   * the final dentry. We expect 'base' to be positive and a directory.
   *
   * Returns 0 and nd will have valid dentry and mnt on success.
   * Returns error and drops reference to input namei data on failure.
   */
  static int link_path_walk(const char *name, struct nameidata *nd)
  {
          struct path next;
          int err;
          
          while (*name=='/')
                  name++;
          if (!*name)
                  return 0;
  
          /* At this point we know we have a real path component. */
          for(;;) {
                  struct qstr this;
                  long len;
                  int type;
  
                  err = may_lookup(nd);
                  if (err)
                          break;
  
                  len = hash_name(name, &this.hash);
                  this.name = name;
                  this.len = len;
  
                  type = LAST_NORM;
                  if (name[0] == '.') switch (len) {
                          case 2:
                                  if (name[1] == '.') {
                                          type = LAST_DOTDOT;
                                          nd->flags |= LOOKUP_JUMPED;
                                  }
                                  break;
                          case 1:
                                  type = LAST_DOT;
                  }
                  if (likely(type == LAST_NORM)) {
                          struct dentry *parent = nd->path.dentry;
                          nd->flags &= ~LOOKUP_JUMPED;
                          if (unlikely(parent->d_flags & DCACHE_OP_HASH)) {
                                  err = parent->d_op->d_hash(parent, nd->inode,
                                                             &this);
                                  if (err < 0)
                                          break;
                          }
                  }
  
                  if (!name[len])
                          goto last_component;
                  /*
                   * If it wasn't NUL, we know it was '/'. Skip that
                   * slash, and continue until no more slashes.
                   */
                  do {
                          len++;
                  } while (unlikely(name[len] == '/'));
                  if (!name[len])
                          goto last_component;
                  name += len;
  
                  err = walk_component(nd, &next, &this, type, LOOKUP_FOLLOW);
                  if (err < 0)
                          return err;
  
                  if (err) {
                          err = nested_symlink(&next, nd);
                          if (err)
                                  return err;
                  }
                  if (can_lookup(nd->inode))
                          continue;
                  err = -ENOTDIR; 
                  break;
                  /* here ends the main loop */
  
  last_component:
                  nd->last = this;
                  nd->last_type = type;
                  return 0;
          }
          terminate_walk(nd);
          return err;
  }
  
  static int path_init(int dfd, const char *name, unsigned int flags,
                       struct nameidata *nd, struct file **fp)
  {
          int retval = 0;
  
          nd->last_type = LAST_ROOT; /* if there are only slashes... */
          nd->flags = flags | LOOKUP_JUMPED;
          nd->depth = 0;
          if (flags & LOOKUP_ROOT) {
                  struct inode *inode = nd->root.dentry->d_inode;
                  if (*name) {
                          if (!can_lookup(inode))
                                  return -ENOTDIR;
                          retval = inode_permission(inode, MAY_EXEC);
                          if (retval)
                                  return retval;
                  }
                  nd->path = nd->root;
                  nd->inode = inode;
                  if (flags & LOOKUP_RCU) {
                          lock_rcu_walk();
                          nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
                  } else {
                          path_get(&nd->path);
                  }
                  return 0;
          }
  
          nd->root.mnt = NULL;
  
          if (*name=='/') {
                  if (flags & LOOKUP_RCU) {
                          lock_rcu_walk();
                          set_root_rcu(nd);
                  } else {
                          set_root(nd);
                          path_get(&nd->root);
                  }
                  nd->path = nd->root;
          } else if (dfd == AT_FDCWD) {
                  if (flags & LOOKUP_RCU) {
                          struct fs_struct *fs = current->fs;
                          unsigned seq;
  
                          lock_rcu_walk();
  
                          do {
                                  seq = read_seqcount_begin(&fs->seq);
                                  nd->path = fs->pwd;
                                  nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
                          } while (read_seqcount_retry(&fs->seq, seq));
                  } else {
                          get_fs_pwd(current->fs, &nd->path);
                  }
          } else {
                  /* Caller must check execute permissions on the starting path component */
                  struct fd f = fdget_raw(dfd);
                  struct dentry *dentry;
  
                  if (!f.file)
                          return -EBADF;
  
                  dentry = f.file->f_path.dentry;
  
                  if (*name) {
                          if (!can_lookup(dentry->d_inode)) {
                                  fdput(f);
                                  return -ENOTDIR;
                          }
                  }
  
                  nd->path = f.file->f_path;
                  if (flags & LOOKUP_RCU) {
                          if (f.need_put)
                                  *fp = f.file;
                          nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
                          lock_rcu_walk();
                  } else {
                          path_get(&nd->path);
                          fdput(f);
                  }
          }
  
          nd->inode = nd->path.dentry->d_inode;
          return 0;
  }
  
  static inline int lookup_last(struct nameidata *nd, struct path *path)
  {
          if (nd->last_type == LAST_NORM && nd->last.name[nd->last.len])
                  nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
  
          nd->flags &= ~LOOKUP_PARENT;
          return walk_component(nd, path, &nd->last, nd->last_type,
                                          nd->flags & LOOKUP_FOLLOW);
  }
  
  /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
  static int path_lookupat(int dfd, const char *name,
                                  unsigned int flags, struct nameidata *nd)
  {
          struct file *base = NULL;
          struct path path;
          int err;
  
          /*
           * Path walking is largely split up into 2 different synchronisation
           * schemes, rcu-walk and ref-walk (explained in
           * Documentation/filesystems/path-lookup.txt). These share much of the
           * path walk code, but some things particularly setup, cleanup, and
           * following mounts are sufficiently divergent that functions are
           * duplicated. Typically there is a function foo(), and its RCU
           * analogue, foo_rcu().
           *
           * -ECHILD is the error number of choice (just to avoid clashes) that
           * is returned if some aspect of an rcu-walk fails. Such an error must
           * be handled by restarting a traditional ref-walk (which will always
           * be able to complete).
           */
          err = path_init(dfd, name, flags | LOOKUP_PARENT, nd, &base);
  
          if (unlikely(err))
                  return err;
  
          current->total_link_count = 0;
          err = link_path_walk(name, nd);
  
          if (!err && !(flags & LOOKUP_PARENT)) {
                  err = lookup_last(nd, &path);
                  while (err > 0) {
                          void *cookie;
                          struct path link = path;
                          err = may_follow_link(&link, nd);
                          if (unlikely(err))
                                  break;
                          nd->flags |= LOOKUP_PARENT;
                          err = follow_link(&link, nd, &cookie);
                          if (err)
                                  break;
                          err = lookup_last(nd, &path);
                          put_link(nd, &link, cookie);
                  }
          }
  
          if (!err)
                  err = complete_walk(nd);
  
          if (!err && nd->flags & LOOKUP_DIRECTORY) {
                  if (!nd->inode->i_op->lookup) {
                          path_put(&nd->path);
                          err = -ENOTDIR;
                  }
          }
  
          if (base)
                  fput(base);
  
          if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
                  path_put(&nd->root);
                  nd->root.mnt = NULL;
          }
          return err;
  }
  
  static int filename_lookup(int dfd, struct filename *name,
                                  unsigned int flags, struct nameidata *nd)
  {
          int retval = path_lookupat(dfd, name->name, flags | LOOKUP_RCU, nd);
          if (unlikely(retval == -ECHILD))
                  retval = path_lookupat(dfd, name->name, flags, nd);
          if (unlikely(retval == -ESTALE))
                  retval = path_lookupat(dfd, name->name,
                                                  flags | LOOKUP_REVAL, nd);
  
          if (likely(!retval))
                  audit_inode(name, nd->path.dentry, flags & LOOKUP_PARENT);
          return retval;
  }
  
  static int do_path_lookup(int dfd, const char *name,
                                  unsigned int flags, struct nameidata *nd)
  {
          struct filename filename = { .name = name };
  
          return filename_lookup(dfd, &filename, flags, nd);
  }
  
  /* does lookup, returns the object with parent locked */
  struct dentry *kern_path_locked(const char *name, struct path *path)
  {
          struct nameidata nd;
          struct dentry *d;
          int err = do_path_lookup(AT_FDCWD, name, LOOKUP_PARENT, &nd);
          if (err)
                  return ERR_PTR(err);
          if (nd.last_type != LAST_NORM) {
                  path_put(&nd.path);
                  return ERR_PTR(-EINVAL);
          }
          mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
          d = __lookup_hash(&nd.last, nd.path.dentry, 0);
          if (IS_ERR(d)) {
                  mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
                  path_put(&nd.path);
                  return d;
          }
          *path = nd.path;
          return d;
  }
  
  int kern_path(const char *name, unsigned int flags, struct path *path)
  {
          struct nameidata nd;
          int res = do_path_lookup(AT_FDCWD, name, flags, &nd);
          if (!res)
                  *path = nd.path;
          return res;
  }
  
  /**
   * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair
   * @dentry:  pointer to dentry of the base directory
   * @mnt: pointer to vfs mount of the base directory
   * @name: pointer to file name
   * @flags: lookup flags
   * @path: pointer to struct path to fill
   */
  int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
                      const char *name, unsigned int flags,
                      struct path *path)
  {
          struct nameidata nd;
          int err;
          nd.root.dentry = dentry;
          nd.root.mnt = mnt;
          BUG_ON(flags & LOOKUP_PARENT);
          /* the first argument of do_path_lookup() is ignored with LOOKUP_ROOT */
          err = do_path_lookup(AT_FDCWD, name, flags | LOOKUP_ROOT, &nd);
          if (!err)
                  *path = nd.path;
          return err;
  }
  
  /*
   * Restricted form of lookup. Doesn't follow links, single-component only,
   * needs parent already locked. Doesn't follow mounts.
   * SMP-safe.
   */
  static struct dentry *lookup_hash(struct nameidata *nd)
  {
          return __lookup_hash(&nd->last, nd->path.dentry, nd->flags);
  }
  
  /**
   * lookup_one_len - filesystem helper to lookup single pathname component
   * @name:       pathname component to lookup
   * @base:       base directory to lookup from
   * @len:        maximum length @len should be interpreted to
   *
   * Note that this routine is purely a helper for filesystem usage and should
   * not be called by generic code.  Also note that by using this function the
   * nameidata argument is passed to the filesystem methods and a filesystem
   * using this helper needs to be prepared for that.
   */
  struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
  {
          struct qstr this;
          unsigned int c;
          int err;
  
          WARN_ON_ONCE(!mutex_is_locked(&base->d_inode->i_mutex));
  
          this.name = name;
          this.len = len;
          this.hash = full_name_hash(name, len);
          if (!len)
                  return ERR_PTR(-EACCES);
  
          if (unlikely(name[0] == '.')) {
                  if (len < 2 || (len == 2 && name[1] == '.'))
                          return ERR_PTR(-EACCES);
          }
  
          while (len--) {
                  c = *(const unsigned char *)name++;
                  if (c == '/' || c == '\0')
                          return ERR_PTR(-EACCES);
          }
          /*
           * See if the low-level filesystem might want
           * to use its own hash..
           */
          if (base->d_flags & DCACHE_OP_HASH) {
                  int err = base->d_op->d_hash(base, base->d_inode, &this);
                  if (err < 0)
                          return ERR_PTR(err);
          }
  
          err = inode_permission(base->d_inode, MAY_EXEC);
          if (err)
                  return ERR_PTR(err);
  
          return __lookup_hash(&this, base, 0);
  }
  
  int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
                   struct path *path, int *empty)
  {
          struct nameidata nd;
          struct filename *tmp = getname_flags(name, flags, empty);
          int err = PTR_ERR(tmp);
          if (!IS_ERR(tmp)) {
  
                  BUG_ON(flags & LOOKUP_PARENT);
  
                  err = filename_lookup(dfd, tmp, flags, &nd);
                  putname(tmp);
                  if (!err)
                          *path = nd.path;
          }
          return err;
  }
  
  int user_path_at(int dfd, const char __user *name, unsigned flags,
                   struct path *path)
  {
          return user_path_at_empty(dfd, name, flags, path, NULL);
  }
  
  /*
   * NB: most callers don't do anything directly with the reference to the
   *     to struct filename, but the nd->last pointer points into the name string
   *     allocated by getname. So we must hold the reference to it until all
   *     path-walking is complete.
   */
  static struct filename *
  user_path_parent(int dfd, const char __user *path, struct nameidata *nd,
                   unsigned int flags)
  {
          struct filename *s = getname(path);
          int error;
  
          /* only LOOKUP_REVAL is allowed in extra flags */
          flags &= LOOKUP_REVAL;
  
          if (IS_ERR(s))
                  return s;
  
          error = filename_lookup(dfd, s, flags | LOOKUP_PARENT, nd);
          if (error) {
                  putname(s);
                  return ERR_PTR(error);
          }
  
          return s;
  }
  
  /*
   * It's inline, so penalty for filesystems that don't use sticky bit is
   * minimal.
   */
  static inline int check_sticky(struct inode *dir, struct inode *inode)
  {
          kuid_t fsuid = current_fsuid();
  
          if (!(dir->i_mode & S_ISVTX))
                  return 0;
          if (uid_eq(inode->i_uid, fsuid))
                  return 0;
          if (uid_eq(dir->i_uid, fsuid))
                  return 0;
          return !inode_capable(inode, CAP_FOWNER);
  }
  
  /*
   *      Check whether we can remove a link victim from directory dir, check
   *  whether the type of victim is right.
   *  1. We can't do it if dir is read-only (done in permission())
   *  2. We should have write and exec permissions on dir
   *  3. We can't remove anything from append-only dir
   *  4. We can't do anything with immutable dir (done in permission())
   *  5. If the sticky bit on dir is set we should either
   *      a. be owner of dir, or
   *      b. be owner of victim, or
   *      c. have CAP_FOWNER capability
   *  6. If the victim is append-only or immutable we can't do antyhing with
   *     links pointing to it.
   *  7. If we were asked to remove a directory and victim isn't one - ENOTDIR.
   *  8. If we were asked to remove a non-directory and victim isn't one - EISDIR.
   *  9. We can't remove a root or mountpoint.
   * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
   *     nfs_async_unlink().
   */
  static int may_delete(struct inode *dir,struct dentry *victim,int isdir)
  {
          int error;
  
          if (!victim->d_inode)
                  return -ENOENT;
  
          BUG_ON(victim->d_parent->d_inode != dir);
          audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE);
  
          error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
          if (error)
                  return error;
          if (IS_APPEND(dir))
                  return -EPERM;
          if (check_sticky(dir, victim->d_inode)||IS_APPEND(victim->d_inode)||
              IS_IMMUTABLE(victim->d_inode) || IS_SWAPFILE(victim->d_inode))
                  return -EPERM;
          if (isdir) {
                  if (!S_ISDIR(victim->d_inode->i_mode))
                          return -ENOTDIR;
                  if (IS_ROOT(victim))
                          return -EBUSY;
          } else if (S_ISDIR(victim->d_inode->i_mode))
                  return -EISDIR;
          if (IS_DEADDIR(dir))
                  return -ENOENT;
          if (victim->d_flags & DCACHE_NFSFS_RENAMED)
                  return -EBUSY;
          return 0;
  }
  
  /*      Check whether we can create an object with dentry child in directory
   *  dir.
   *  1. We can't do it if child already exists (open has special treatment for
   *     this case, but since we are inlined it's OK)
   *  2. We can't do it if dir is read-only (done in permission())
   *  3. We should have write and exec permissions on dir
   *  4. We can't do it if dir is immutable (done in permission())
   */
  static inline int may_create(struct inode *dir, struct dentry *child)
  {
          if (child->d_inode)
                  return -EEXIST;
          if (IS_DEADDIR(dir))
                  return -ENOENT;
          return inode_permission(dir, MAY_WRITE | MAY_EXEC);
  }
  
  /*
   * p1 and p2 should be directories on the same fs.
   */
  struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
  {
          struct dentry *p;
  
          if (p1 == p2) {
                  mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
                  return NULL;
          }
  
          mutex_lock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
  
          p = d_ancestor(p2, p1);
          if (p) {
                  mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT);
                  mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_CHILD);
                  return p;
          }
  
          p = d_ancestor(p1, p2);
          if (p) {
                  mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
                  mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD);
                  return p;
          }
  
          mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
          mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD);
          return NULL;
  }
  
  void unlock_rename(struct dentry *p1, struct dentry *p2)
  {
          mutex_unlock(&p1->d_inode->i_mutex);
          if (p1 != p2) {
                  mutex_unlock(&p2->d_inode->i_mutex);
                  mutex_unlock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
          }
  }
  
  int vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
                  bool want_excl)
  {
          int error = may_create(dir, dentry);
          if (error)
                  return error;
  
          if (!dir->i_op->create)
                  return -EACCES; /* shouldn't it be ENOSYS? */
          mode &= S_IALLUGO;
          mode |= S_IFREG;
          error = security_inode_create(dir, dentry, mode);
          if (error)
                  return error;
          error = dir->i_op->create(dir, dentry, mode, want_excl);
          if (!error)
                  fsnotify_create(dir, dentry);
          return error;
  }
  
  static int may_open(struct path *path, int acc_mode, int flag)
  {
          struct dentry *dentry = path->dentry;
          struct inode *inode = dentry->d_inode;
          int error;
  
          /* O_PATH? */
          if (!acc_mode)
                  return 0;
  
          if (!inode)
                  return -ENOENT;
  
          switch (inode->i_mode & S_IFMT) {
          case S_IFLNK:
                  return -ELOOP;
          case S_IFDIR:
                  if (acc_mode & MAY_WRITE)
                          return -EISDIR;
                  break;
          case S_IFBLK:
          case S_IFCHR:
                  if (path->mnt->mnt_flags & MNT_NODEV)
                          return -EACCES;
                  /*FALLTHRU*/
          case S_IFIFO:
          case S_IFSOCK:
                  flag &= ~O_TRUNC;
                  break;
          }
  
          error = inode_permission(inode, acc_mode);
          if (error)
                  return error;
  
          /*
           * An append-only file must be opened in append mode for writing.
           */
          if (IS_APPEND(inode)) {
                  if  ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
                          return -EPERM;
                  if (flag & O_TRUNC)
                          return -EPERM;
          }
  
          /* O_NOATIME can only be set by the owner or superuser */
          if (flag & O_NOATIME && !inode_owner_or_capable(inode))
                  return -EPERM;
  
          return 0;
  }
  
  static int handle_truncate(struct file *filp)
  {
          struct path *path = &filp->f_path;
          struct inode *inode = path->dentry->d_inode;
          int error = get_write_access(inode);
          if (error)
                  return error;
          /*
           * Refuse to truncate files with mandatory locks held on them.
           */
          error = locks_verify_locked(inode);
          if (!error)
                  error = security_path_truncate(path);
          if (!error) {
                  error = do_truncate(path->dentry, 0,
                                      ATTR_MTIME|ATTR_CTIME|ATTR_OPEN,
                                      filp);
          }
          put_write_access(inode);
          return error;
  }
  
  static inline int open_to_namei_flags(int flag)
  {
          if ((flag & O_ACCMODE) == 3)
                  flag--;
          return flag;
  }
  
  static int may_o_create(struct path *dir, struct dentry *dentry, umode_t mode)
  {
          int error = security_path_mknod(dir, dentry, mode, 0);
          if (error)
                  return error;
  
          error = inode_permission(dir->dentry->d_inode, MAY_WRITE | MAY_EXEC);
          if (error)
                  return error;
  
          return security_inode_create(dir->dentry->d_inode, dentry, mode);
  }
  
  /*
   * Attempt to atomically look up, create and open a file from a negative
   * dentry.
   *
   * Returns 0 if successful.  The file will have been created and attached to
   * @file by the filesystem calling finish_open().
   *
   * Returns 1 if the file was looked up only or didn't need creating.  The
   * caller will need to perform the open themselves.  @path will have been
   * updated to point to the new dentry.  This may be negative.
   *
   * Returns an error code otherwise.
   */
  static int atomic_open(struct nameidata *nd, struct dentry *dentry,
                          struct path *path, struct file *file,
                          const struct open_flags *op,
                          bool got_write, bool need_lookup,
                          int *opened)
  {
          struct inode *dir =  nd->path.dentry->d_inode;
          unsigned open_flag = open_to_namei_flags(op->open_flag);
          umode_t mode;
          int error;
          int acc_mode;
          int create_error = 0;
          struct dentry *const DENTRY_NOT_SET = (void *) -1UL;
  
          BUG_ON(dentry->d_inode);
  
          /* Don't create child dentry for a dead directory. */
          if (unlikely(IS_DEADDIR(dir))) {
                  error = -ENOENT;
                  goto out;
          }
  
          mode = op->mode;
          if ((open_flag & O_CREAT) && !IS_POSIXACL(dir))
                  mode &= ~current_umask();
  
          if ((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT)) {
                  open_flag &= ~O_TRUNC;
                  *opened |= FILE_CREATED;
          }
  
          /*
           * Checking write permission is tricky, bacuse we don't know if we are
           * going to actually need it: O_CREAT opens should work as long as the
           * file exists.  But checking existence breaks atomicity.  The trick is
           * to check access and if not granted clear O_CREAT from the flags.
           *
           * Another problem is returing the "right" error value (e.g. for an
           * O_EXCL open we want to return EEXIST not EROFS).
           */
          if (((open_flag & (O_CREAT | O_TRUNC)) ||
              (open_flag & O_ACCMODE) != O_RDONLY) && unlikely(!got_write)) {
                  if (!(open_flag & O_CREAT)) {
                          /*
                           * No O_CREATE -> atomicity not a requirement -> fall
                           * back to lookup + open
                           */
                          goto no_open;
                  } else if (open_flag & (O_EXCL | O_TRUNC)) {
                          /* Fall back and fail with the right error */
                          create_error = -EROFS;
                          goto no_open;
                  } else {
                          /* No side effects, safe to clear O_CREAT */
                          create_error = -EROFS;
                          open_flag &= ~O_CREAT;
                  }
          }
  
          if (open_flag & O_CREAT) {
                  error = may_o_create(&nd->path, dentry, mode);
                  if (error) {
                          create_error = error;
                          if (open_flag & O_EXCL)
                                  goto no_open;
                          open_flag &= ~O_CREAT;
                  }
          }
  
          if (nd->flags & LOOKUP_DIRECTORY)
                  open_flag |= O_DIRECTORY;
  
          file->f_path.dentry = DENTRY_NOT_SET;
          file->f_path.mnt = nd->path.mnt;
          error = dir->i_op->atomic_open(dir, dentry, file, open_flag, mode,
                                        opened);
          if (error < 0) {
                  if (create_error && error == -ENOENT)
                          error = create_error;
                  goto out;
          }
  
          acc_mode = op->acc_mode;
          if (*opened & FILE_CREATED) {
                  fsnotify_create(dir, dentry);
                  acc_mode = MAY_OPEN;
          }
  
          if (error) {    /* returned 1, that is */
                  if (WARN_ON(file->f_path.dentry == DENTRY_NOT_SET)) {
                          error = -EIO;
                          goto out;
                  }
                  if (file->f_path.dentry) {
                          dput(dentry);
                          dentry = file->f_path.dentry;
                  }
                  if (create_error && dentry->d_inode == NULL) {
                          error = create_error;
                          goto out;
                  }
                  goto looked_up;
          }
  
          /*
           * We didn't have the inode before the open, so check open permission
           * here.
           */
          error = may_open(&file->f_path, acc_mode, open_flag);
          if (error)
                  fput(file);
  
  out:
          dput(dentry);
          return error;
  
  no_open:
          if (need_lookup) {
                  dentry = lookup_real(dir, dentry, nd->flags);
                  if (IS_ERR(dentry))
                          return PTR_ERR(dentry);
  
                  if (create_error) {
                          int open_flag = op->open_flag;
  
                          error = create_error;
                          if ((open_flag & O_EXCL)) {
                                  if (!dentry->d_inode)
                                          goto out;
                          } else if (!dentry->d_inode) {
                                  goto out;
                          } else if ((open_flag & O_TRUNC) &&
                                     S_ISREG(dentry->d_inode->i_mode)) {
                                  goto out;
                          }
                          /* will fail later, go on to get the right error */
                  }
          }
  looked_up:
          path->dentry = dentry;
          path->mnt = nd->path.mnt;
          return 1;
  }
  
  /*
   * Look up and maybe create and open the last component.
   *
   * Must be called with i_mutex held on parent.
   *
   * Returns 0 if the file was successfully atomically created (if necessary) and
   * opened.  In this case the file will be returned attached to @file.
   *
   * Returns 1 if the file was not completely opened at this time, though lookups
   * and creations will have been performed and the dentry returned in @path will
   * be positive upon return if O_CREAT was specified.  If O_CREAT wasn't
   * specified then a negative dentry may be returned.
   *
   * An error code is returned otherwise.
   *
   * FILE_CREATE will be set in @*opened if the dentry was created and will be
   * cleared otherwise prior to returning.
   */
  static int lookup_open(struct nameidata *nd, struct path *path,
                          struct file *file,
                          const struct open_flags *op,
                          bool got_write, int *opened)
  {
          struct dentry *dir = nd->path.dentry;
          struct inode *dir_inode = dir->d_inode;
          struct dentry *dentry;
          int error;
          bool need_lookup;
  
          *opened &= ~FILE_CREATED;
          dentry = lookup_dcache(&nd->last, dir, nd->flags, &need_lookup);
          if (IS_ERR(dentry))
                  return PTR_ERR(dentry);
  
          /* Cached positive dentry: will open in f_op->open */
          if (!need_lookup && dentry->d_inode)
                  goto out_no_open;
  
          if ((nd->flags & LOOKUP_OPEN) && dir_inode->i_op->atomic_open) {
                  return atomic_open(nd, dentry, path, file, op, got_write,
                                     need_lookup, opened);
          }
  
          if (need_lookup) {
                  BUG_ON(dentry->d_inode);
  
                  dentry = lookup_real(dir_inode, dentry, nd->flags);
                  if (IS_ERR(dentry))
                          return PTR_ERR(dentry);
          }
  
          /* Negative dentry, just create the file */
          if (!dentry->d_inode && (op->open_flag & O_CREAT)) {
                  umode_t mode = op->mode;
                  if (!IS_POSIXACL(dir->d_inode))
                          mode &= ~current_umask();
                  /*
                   * This write is needed to ensure that a
                   * rw->ro transition does not occur between
                   * the time when the file is created and when
                   * a permanent write count is taken through
                   * the 'struct file' in finish_open().
                   */
                  if (!got_write) {
                          error = -EROFS;
                          goto out_dput;
                  }
                  *opened |= FILE_CREATED;
                  error = security_path_mknod(&nd->path, dentry, mode, 0);
                  if (error)
                          goto out_dput;
                  error = vfs_create(dir->d_inode, dentry, mode,
                                     nd->flags & LOOKUP_EXCL);
                  if (error)
                          goto out_dput;
          }
  out_no_open:
          path->dentry = dentry;
          path->mnt = nd->path.mnt;
          return 1;
  
  out_dput:
          dput(dentry);
          return error;
  }
  
  /*
   * Handle the last step of open()
   */
  static int do_last(struct nameidata *nd, struct path *path,
                     struct file *file, const struct open_flags *op,
                     int *opened, struct filename *name)
  {
          struct dentry *dir = nd->path.dentry;
          int open_flag = op->open_flag;
          bool will_truncate = (open_flag & O_TRUNC) != 0;
          bool got_write = false;
          int acc_mode = op->acc_mode;
          struct inode *inode;
          bool symlink_ok = false;
          struct path save_parent = { .dentry = NULL, .mnt = NULL };
          bool retried = false;
          int error;
  
          nd->flags &= ~LOOKUP_PARENT;
          nd->flags |= op->intent;
  
          switch (nd->last_type) {
          case LAST_DOTDOT:
          case LAST_DOT:
                  error = handle_dots(nd, nd->last_type);
                  if (error)
                          return error;
                  /* fallthrough */
          case LAST_ROOT:
                  error = complete_walk(nd);
                  if (error)
                          return error;
                  audit_inode(name, nd->path.dentry, 0);
                  if (open_flag & O_CREAT) {
                          error = -EISDIR;
                          goto out;
                  }
                  goto finish_open;
          case LAST_BIND:
                  error = complete_walk(nd);
                  if (error)
                          return error;
                  audit_inode(name, dir, 0);
                  goto finish_open;
          }
  
          if (!(open_flag & O_CREAT)) {
                  if (nd->last.name[nd->last.len])
                          nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
                  if (open_flag & O_PATH && !(nd->flags & LOOKUP_FOLLOW))
                          symlink_ok = true;
                  /* we _can_ be in RCU mode here */
                  error = lookup_fast(nd, &nd->last, path, &inode);
                  if (likely(!error))
                          goto finish_lookup;
  
                  if (error < 0)
                          goto out;
  
                  BUG_ON(nd->inode != dir->d_inode);
          } else {
                  /* create side of things */
                  /*
                   * This will *only* deal with leaving RCU mode - LOOKUP_JUMPED
                   * has been cleared when we got to the last component we are
                   * about to look up
                   */
                  error = complete_walk(nd);
                  if (error)
                          return error;
  
                  audit_inode(name, dir, 0);
                  error = -EISDIR;
                  /* trailing slashes? */
                  if (nd->last.name[nd->last.len])
                          goto out;
          }
  
  retry_lookup:
          if (op->open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) {
                  error = mnt_want_write(nd->path.mnt);
                  if (!error)
                          got_write = true;
                  /*
                   * do _not_ fail yet - we might not need that or fail with
                   * a different error; let lookup_open() decide; we'll be
                   * dropping this one anyway.
                   */
          }
          mutex_lock(&dir->d_inode->i_mutex);
          error = lookup_open(nd, path, file, op, got_write, opened);
          mutex_unlock(&dir->d_inode->i_mutex);
  
          if (error <= 0) {
                  if (error)
                          goto out;
  
                  if ((*opened & FILE_CREATED) ||
                      !S_ISREG(file->f_path.dentry->d_inode->i_mode))
                          will_truncate = false;
  
                  audit_inode(name, file->f_path.dentry, 0);
                  goto opened;
          }
  
          if (*opened & FILE_CREATED) {
                  /* Don't check for write permission, don't truncate */
                  open_flag &= ~O_TRUNC;
                  will_truncate = false;
                  acc_mode = MAY_OPEN;
                  path_to_nameidata(path, nd);
                  goto finish_open_created;
          }
  
          /*
           * create/update audit record if it already exists.
           */
          if (path->dentry->d_inode)
                  audit_inode(name, path->dentry, 0);
  
          /*
           * If atomic_open() acquired write access it is dropped now due to
           * possible mount and symlink following (this might be optimized away if
           * necessary...)
           */
          if (got_write) {
                  mnt_drop_write(nd->path.mnt);
                  got_write = false;
          }
  
          error = -EEXIST;
          if ((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT))
                  goto exit_dput;
  
          error = follow_managed(path, nd->flags);
          if (error < 0)
                  goto exit_dput;
  
          if (error)
                  nd->flags |= LOOKUP_JUMPED;
  
          BUG_ON(nd->flags & LOOKUP_RCU);
          inode = path->dentry->d_inode;
  finish_lookup:
          /* we _can_ be in RCU mode here */
          error = -ENOENT;
          if (!inode) {
                  path_to_nameidata(path, nd);
                  goto out;
          }
  
          if (should_follow_link(inode, !symlink_ok)) {
                  if (nd->flags & LOOKUP_RCU) {
                          if (unlikely(unlazy_walk(nd, path->dentry))) {
                                  error = -ECHILD;
                                  goto out;
                          }
                  }
                  BUG_ON(inode != path->dentry->d_inode);
                  return 1;
          }
  
          if ((nd->flags & LOOKUP_RCU) || nd->path.mnt != path->mnt) {
                  path_to_nameidata(path, nd);
          } else {
                  save_parent.dentry = nd->path.dentry;
                  save_parent.mnt = mntget(path->mnt);
                  nd->path.dentry = path->dentry;
  
          }
          nd->inode = inode;
          /* Why this, you ask?  _Now_ we might have grown LOOKUP_JUMPED... */
          error = complete_walk(nd);
          if (error) {
                  path_put(&save_parent);
                  return error;
          }
          error = -EISDIR;
          if ((open_flag & O_CREAT) && S_ISDIR(nd->inode->i_mode))
                  goto out;
          error = -ENOTDIR;
          if ((nd->flags & LOOKUP_DIRECTORY) && !nd->inode->i_op->lookup)
                  goto out;
          audit_inode(name, nd->path.dentry, 0);
  finish_open:
          if (!S_ISREG(nd->inode->i_mode))
                  will_truncate = false;
  
          if (will_truncate) {
                  error = mnt_want_write(nd->path.mnt);
                  if (error)
                          goto out;
                  got_write = true;
          }
  finish_open_created:
          error = may_open(&nd->path, acc_mode, open_flag);
          if (error)
                  goto out;
          file->f_path.mnt = nd->path.mnt;
          error = finish_open(file, nd->path.dentry, NULL, opened);
          if (error) {
                  if (error == -EOPENSTALE)
                          goto stale_open;
                  goto out;
          }
  opened:
          error = open_check_o_direct(file);
          if (error)
                  goto exit_fput;
          error = ima_file_check(file, op->acc_mode);
          if (error)
                  goto exit_fput;
  
          if (will_truncate) {
                  error = handle_truncate(file);
                  if (error)
                          goto exit_fput;
          }
  out:
          if (got_write)
                  mnt_drop_write(nd->path.mnt);
          path_put(&save_parent);
          terminate_walk(nd);
          return error;
  
  exit_dput:
          path_put_conditional(path, nd);
          goto out;
  exit_fput:
          fput(file);
          goto out;
  
  stale_open:
          /* If no saved parent or already retried then can't retry */
          if (!save_parent.dentry || retried)
                  goto out;
  
          BUG_ON(save_parent.dentry != dir);
          path_put(&nd->path);
          nd->path = save_parent;
          nd->inode = dir->d_inode;
          save_parent.mnt = NULL;
          save_parent.dentry = NULL;
          if (got_write) {
                  mnt_drop_write(nd->path.mnt);
                  got_write = false;
          }
          retried = true;
          goto retry_lookup;
  }
  
  static struct file *path_openat(int dfd, struct filename *pathname,
                  struct nameidata *nd, const struct open_flags *op, int flags)
  {
          struct file *base = NULL;
          struct file *file;
          struct path path;
          int opened = 0;
          int error;
  
          file = get_empty_filp();
          if (!file)
                  return ERR_PTR(-ENFILE);
  
          file->f_flags = op->open_flag;
  
          error = path_init(dfd, pathname->name, flags | LOOKUP_PARENT, nd, &base);
          if (unlikely(error))
                  goto out;
  
          current->total_link_count = 0;
          error = link_path_walk(pathname->name, nd);
          if (unlikely(error))
                  goto out;
  
          error = do_last(nd, &path, file, op, &opened, pathname);
          while (unlikely(error > 0)) { /* trailing symlink */
                  struct path link = path;
                  void *cookie;
                  if (!(nd->flags & LOOKUP_FOLLOW)) {
                          path_put_conditional(&path, nd);
                          path_put(&nd->path);
                          error = -ELOOP;
                          break;
                  }
                  error = may_follow_link(&link, nd);
                  if (unlikely(error))
                          break;
                  nd->flags |= LOOKUP_PARENT;
                  nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL);
                  error = follow_link(&link, nd, &cookie);
                  if (unlikely(error))
                          break;
                  error = do_last(nd, &path, file, op, &opened, pathname);
                  put_link(nd, &link, cookie);
          }
  out:
          if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT))
                  path_put(&nd->root);
          if (base)
                  fput(base);
          if (!(opened & FILE_OPENED)) {
                  BUG_ON(!error);
                  put_filp(file);
          }
          if (unlikely(error)) {
                  if (error == -EOPENSTALE) {
                          if (flags & LOOKUP_RCU)
                                  error = -ECHILD;
                          else
                                  error = -ESTALE;
                  }
                  file = ERR_PTR(error);
          }
          return file;
  }
  
  struct file *do_filp_open(int dfd, struct filename *pathname,
                  const struct open_flags *op, int flags)
  {
          struct nameidata nd;
          struct file *filp;
  
          filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_RCU);
          if (unlikely(filp == ERR_PTR(-ECHILD)))
                  filp = path_openat(dfd, pathname, &nd, op, flags);
          if (unlikely(filp == ERR_PTR(-ESTALE)))
                  filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_REVAL);
          return filp;
  }
  
  struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
                  const char *name, const struct open_flags *op, int flags)
  {
          struct nameidata nd;
          struct file *file;
          struct filename filename = { .name = name };
  
          nd.root.mnt = mnt;
          nd.root.dentry = dentry;
  
          flags |= LOOKUP_ROOT;
  
          if (dentry->d_inode->i_op->follow_link && op->intent & LOOKUP_OPEN)
                  return ERR_PTR(-ELOOP);
  
          file = path_openat(-1, &filename, &nd, op, flags | LOOKUP_RCU);
          if (unlikely(file == ERR_PTR(-ECHILD)))
                  file = path_openat(-1, &filename, &nd, op, flags);
          if (unlikely(file == ERR_PTR(-ESTALE)))
                  file = path_openat(-1, &filename, &nd, op, flags | LOOKUP_REVAL);
          return file;
  }
  
  struct dentry *kern_path_create(int dfd, const char *pathname,
                                  struct path *path, unsigned int lookup_flags)
  {
          struct dentry *dentry = ERR_PTR(-EEXIST);
          struct nameidata nd;
          int err2;
          int error;
          bool is_dir = (lookup_flags & LOOKUP_DIRECTORY);
  
          /*
           * Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any
           * other flags passed in are ignored!
           */
          lookup_flags &= LOOKUP_REVAL;
  
          error = do_path_lookup(dfd, pathname, LOOKUP_PARENT|lookup_flags, &nd);
          if (error)
                  return ERR_PTR(error);
  
          /*
           * Yucky last component or no last component at all?
           * (foo/., foo/.., /////)
           */
          if (nd.last_type != LAST_NORM)
                  goto out;
          nd.flags &= ~LOOKUP_PARENT;
          nd.flags |= LOOKUP_CREATE | LOOKUP_EXCL;
  
          /* don't fail immediately if it's r/o, at least try to report other errors */
          err2 = mnt_want_write(nd.path.mnt);
          /*
           * Do the final lookup.
           */
          mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
          dentry = lookup_hash(&nd);
          if (IS_ERR(dentry))
                  goto unlock;
  
          error = -EEXIST;
          if (dentry->d_inode)
                  goto fail;
          /*
           * Special case - lookup gave negative, but... we had foo/bar/
           * From the vfs_mknod() POV we just have a negative dentry -
           * all is fine. Let's be bastards - you had / on the end, you've
           * been asking for (non-existent) directory. -ENOENT for you.
           */
          if (unlikely(!is_dir && nd.last.name[nd.last.len])) {
                  error = -ENOENT;
                  goto fail;
          }
          if (unlikely(err2)) {
                  error = err2;
                  goto fail;
          }
          *path = nd.path;
          return dentry;
  fail:
          dput(dentry);
          dentry = ERR_PTR(error);
  unlock:
          mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
          if (!err2)
                  mnt_drop_write(nd.path.mnt);
  out:
          path_put(&nd.path);
          return dentry;
  }
  EXPORT_SYMBOL(kern_path_create);
  
  void done_path_create(struct path *path, struct dentry *dentry)
  {
          dput(dentry);
          mutex_unlock(&path->dentry->d_inode->i_mutex);
          mnt_drop_write(path->mnt);
          path_put(path);
  }
  EXPORT_SYMBOL(done_path_create);
  
  struct dentry *user_path_create(int dfd, const char __user *pathname,
                                  struct path *path, unsigned int lookup_flags)
  {
          struct filename *tmp = getname(pathname);
          struct dentry *res;
          if (IS_ERR(tmp))
                  return ERR_CAST(tmp);
          res = kern_path_create(dfd, tmp->name, path, lookup_flags);
          putname(tmp);
          return res;
  }
  EXPORT_SYMBOL(user_path_create);
  
  int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
  {
          int error = may_create(dir, dentry);
  
          if (error)
                  return error;
  
          if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD))
                  return -EPERM;
  
          if (!dir->i_op->mknod)
                  return -EPERM;
  
          error = devcgroup_inode_mknod(mode, dev);
          if (error)
                  return error;
  
          error = security_inode_mknod(dir, dentry, mode, dev);
          if (error)
                  return error;
  
          error = dir->i_op->mknod(dir, dentry, mode, dev);
          if (!error)
                  fsnotify_create(dir, dentry);
          return error;
  }
  
  static int may_mknod(umode_t mode)
  {
          switch (mode & S_IFMT) {
          case S_IFREG:
          case S_IFCHR:
          case S_IFBLK:
          case S_IFIFO:
          case S_IFSOCK:
          case 0: /* zero mode translates to S_IFREG */
                  return 0;
          case S_IFDIR:
                  return -EPERM;
          default:
                  return -EINVAL;
          }
  }
  
  SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
                  unsigned, dev)
  {
          struct dentry *dentry;
          struct path path;
          int error;
          unsigned int lookup_flags = 0;
  
          error = may_mknod(mode);
          if (error)
                  return error;
  retry:
          dentry = user_path_create(dfd, filename, &path, lookup_flags);
          if (IS_ERR(dentry))
                  return PTR_ERR(dentry);
  
          if (!IS_POSIXACL(path.dentry->d_inode))
                  mode &= ~current_umask();
          error = security_path_mknod(&path, dentry, mode, dev);
          if (error)
                  goto out;
          switch (mode & S_IFMT) {
                  case 0: case S_IFREG:
                          error = vfs_create(path.dentry->d_inode,dentry,mode,true);
                          break;
                  case S_IFCHR: case S_IFBLK:
                          error = vfs_mknod(path.dentry->d_inode,dentry,mode,
                                          new_decode_dev(dev));
                          break;
                  case S_IFIFO: case S_IFSOCK:
                          error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
                          break;
          }
  out:
          done_path_create(&path, dentry);
          if (retry_estale(error, lookup_flags)) {
                  lookup_flags |= LOOKUP_REVAL;
                  goto retry;
          }
          return error;
  }
  
  SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, dev)
  {
          return sys_mknodat(AT_FDCWD, filename, mode, dev);
  }
  
  int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
  {
          int error = may_create(dir, dentry);
          unsigned max_links = dir->i_sb->s_max_links;
  
          if (error)
                  return error;
  
          if (!dir->i_op->mkdir)
                  return -EPERM;
  
          mode &= (S_IRWXUGO|S_ISVTX);
          error = security_inode_mkdir(dir, dentry, mode);
          if (error)
                  return error;
  
          if (max_links && dir->i_nlink >= max_links)
                  return -EMLINK;
  
          error = dir->i_op->mkdir(dir, dentry, mode);
          if (!error)
                  fsnotify_mkdir(dir, dentry);
          return error;
  }
  
  SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
  {
          struct dentry *dentry;
          struct path path;
          int error;
          unsigned int lookup_flags = LOOKUP_DIRECTORY;
  
  retry:
          dentry = user_path_create(dfd, pathname, &path, lookup_flags);
          if (IS_ERR(dentry))
                  return PTR_ERR(dentry);
  
          if (!IS_POSIXACL(path.dentry->d_inode))
                  mode &= ~current_umask();
          error = security_path_mkdir(&path, dentry, mode);
          if (!error)
                  error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
          done_path_create(&path, dentry);
          if (retry_estale(error, lookup_flags)) {
                  lookup_flags |= LOOKUP_REVAL;
                  goto retry;
          }
          return error;
  }
  
  SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode)
  {
          return sys_mkdirat(AT_FDCWD, pathname, mode);
  }
  
  /*
   * The dentry_unhash() helper will try to drop the dentry early: we
   * should have a usage count of 1 if we're the only user of this
   * dentry, and if that is true (possibly after pruning the dcache),
   * then we drop the dentry now.
   *
   * A low-level filesystem can, if it choses, legally
   * do a
   *
   *      if (!d_unhashed(dentry))
   *              return -EBUSY;
   *
   * if it cannot handle the case of removing a directory
   * that is still in use by something else..
   */
  void dentry_unhash(struct dentry *dentry)
  {
          shrink_dcache_parent(dentry);
          spin_lock(&dentry->d_lock);
          if (dentry->d_count == 1)
                  __d_drop(dentry);
          spin_unlock(&dentry->d_lock);
  }
  
  int vfs_rmdir(struct inode *dir, struct dentry *dentry)
  {
          int error = may_delete(dir, dentry, 1);
  
          if (error)
                  return error;
  
          if (!dir->i_op->rmdir)
                  return -EPERM;
  
          dget(dentry);
          mutex_lock(&dentry->d_inode->i_mutex);
  
          error = -EBUSY;
          if (d_mountpoint(dentry))
                  goto out;
  
          error = security_inode_rmdir(dir, dentry);
          if (error)
                  goto out;
  
          shrink_dcache_parent(dentry);
          error = dir->i_op->rmdir(dir, dentry);
          if (error)
                  goto out;
  
          dentry->d_inode->i_flags |= S_DEAD;
          dont_mount(dentry);
  
  out:
          mutex_unlock(&dentry->d_inode->i_mutex);
          dput(dentry);
          if (!error)
                  d_delete(dentry);
          return error;
  }
  
  static long do_rmdir(int dfd, const char __user *pathname)
  {
          int error = 0;
          struct filename *name;
          struct dentry *dentry;
          struct nameidata nd;
          unsigned int lookup_flags = 0;
  retry:
          name = user_path_parent(dfd, pathname, &nd, lookup_flags);
          if (IS_ERR(name))
                  return PTR_ERR(name);
  
          switch(nd.last_type) {
          case LAST_DOTDOT:
                  error = -ENOTEMPTY;
                  goto exit1;
          case LAST_DOT:
                  error = -EINVAL;
                  goto exit1;
          case LAST_ROOT:
                  error = -EBUSY;
                  goto exit1;
          }
  
          nd.flags &= ~LOOKUP_PARENT;
          error = mnt_want_write(nd.path.mnt);
          if (error)
                  goto exit1;
  
          mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
          dentry = lookup_hash(&nd);
          error = PTR_ERR(dentry);
          if (IS_ERR(dentry))
                  goto exit2;
          if (!dentry->d_inode) {
                  error = -ENOENT;
                  goto exit3;
          }
          error = security_path_rmdir(&nd.path, dentry);
          if (error)
                  goto exit3;
          error = vfs_rmdir(nd.path.dentry->d_inode, dentry);
  exit3:
          dput(dentry);
  exit2:
          mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
          mnt_drop_write(nd.path.mnt);
  exit1:
          path_put(&nd.path);
          putname(name);
          if (retry_estale(error, lookup_flags)) {
                  lookup_flags |= LOOKUP_REVAL;
                  goto retry;
          }
          return error;
  }
  
  SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
  {
          return do_rmdir(AT_FDCWD, pathname);
  }
  
  int vfs_unlink(struct inode *dir, struct dentry *dentry)
  {
          int error = may_delete(dir, dentry, 0);
  
          if (error)
                  return error;
  
          if (!dir->i_op->unlink)
                  return -EPERM;
  
          mutex_lock(&dentry->d_inode->i_mutex);
          if (d_mountpoint(dentry))
                  error = -EBUSY;
          else {
                  error = security_inode_unlink(dir, dentry);
                  if (!error) {
                          error = dir->i_op->unlink(dir, dentry);
                          if (!error)
                                  dont_mount(dentry);
                  }
          }
          mutex_unlock(&dentry->d_inode->i_mutex);
  
          /* We don't d_delete() NFS sillyrenamed files--they still exist. */
          if (!error && !(dentry->d_flags & DCACHE_NFSFS_RENAMED)) {
                  fsnotify_link_count(dentry->d_inode);
                  d_delete(dentry);
          }
  
          return error;
  }
  
  /*
   * Make sure that the actual truncation of the file will occur outside its
   * directory's i_mutex.  Truncate can take a long time if there is a lot of
   * writeout happening, and we don't want to prevent access to the directory
   * while waiting on the I/O.
   */
  static long do_unlinkat(int dfd, const char __user *pathname)
  {
          int error;
          struct filename *name;
          struct dentry *dentry;
          struct nameidata nd;
          struct inode *inode = NULL;
          unsigned int lookup_flags = 0;
  retry:
          name = user_path_parent(dfd, pathname, &nd, lookup_flags);
          if (IS_ERR(name))
                  return PTR_ERR(name);
  
          error = -EISDIR;
          if (nd.last_type != LAST_NORM)
                  goto exit1;
  
          nd.flags &= ~LOOKUP_PARENT;
          error = mnt_want_write(nd.path.mnt);
          if (error)
                  goto exit1;
  
          mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
          dentry = lookup_hash(&nd);
          error = PTR_ERR(dentry);
          if (!IS_ERR(dentry)) {
                  /* Why not before? Because we want correct error value */
                  if (nd.last.name[nd.last.len])
                          goto slashes;
                  inode = dentry->d_inode;
                  if (!inode)
                          goto slashes;
                  ihold(inode);
                  error = security_path_unlink(&nd.path, dentry);
                  if (error)
                          goto exit2;
                  error = vfs_unlink(nd.path.dentry->d_inode, dentry);
  exit2:
                  dput(dentry);
          }
          mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
          if (inode)
                  iput(inode);    /* truncate the inode here */
          mnt_drop_write(nd.path.mnt);
  exit1:
          path_put(&nd.path);
          putname(name);
          if (retry_estale(error, lookup_flags)) {
                  lookup_flags |= LOOKUP_REVAL;
                  inode = NULL;
                  goto retry;
          }
          return error;
  
  slashes:
          error = !dentry->d_inode ? -ENOENT :
                  S_ISDIR(dentry->d_inode->i_mode) ? -EISDIR : -ENOTDIR;
          goto exit2;
  }
  
  SYSCALL_DEFINE3(unlinkat, int, dfd, const char __user *, pathname, int, flag)
  {
          if ((flag & ~AT_REMOVEDIR) != 0)
                  return -EINVAL;
  
          if (flag & AT_REMOVEDIR)
                  return do_rmdir(dfd, pathname);
  
          return do_unlinkat(dfd, pathname);
  }
  
  SYSCALL_DEFINE1(unlink, const char __user *, pathname)
  {
          return do_unlinkat(AT_FDCWD, pathname);
  }
  
  int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname)
  {
          int error = may_create(dir, dentry);
  
          if (error)
                  return error;
  
          if (!dir->i_op->symlink)
                  return -EPERM;
  
          error = security_inode_symlink(dir, dentry, oldname);
          if (error)
                  return error;
  
          error = dir->i_op->symlink(dir, dentry, oldname);
          if (!error)
                  fsnotify_create(dir, dentry);
          return error;
  }
  
  SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
                  int, newdfd, const char __user *, newname)
  {
          int error;
          struct filename *from;
          struct dentry *dentry;
          struct path path;
          unsigned int lookup_flags = 0;
  
          from = getname(oldname);
          if (IS_ERR(from))
                  return PTR_ERR(from);
  retry:
          dentry = user_path_create(newdfd, newname, &path, lookup_flags);
          error = PTR_ERR(dentry);
          if (IS_ERR(dentry))
                  goto out_putname;
  
          error = security_path_symlink(&path, dentry, from->name);
          if (!error)
                  error = vfs_symlink(path.dentry->d_inode, dentry, from->name);
          done_path_create(&path, dentry);
          if (retry_estale(error, lookup_flags)) {
                  lookup_flags |= LOOKUP_REVAL;
                  goto retry;
          }
  out_putname:
          putname(from);
          return error;
  }
  
  SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newname)
  {
          return sys_symlinkat(oldname, AT_FDCWD, newname);
  }
  
  int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry)
  {
          struct inode *inode = old_dentry->d_inode;
          unsigned max_links = dir->i_sb->s_max_links;
          int error;
  
          if (!inode)
                  return -ENOENT;
  
          error = may_create(dir, new_dentry);
          if (error)
                  return error;
  
          if (dir->i_sb != inode->i_sb)
                  return -EXDEV;
  
          /*
           * A link to an append-only or immutable file cannot be created.
           */
          if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
                  return -EPERM;
          if (!dir->i_op->link)
                  return -EPERM;
          if (S_ISDIR(inode->i_mode))
                  return -EPERM;
  
          error = security_inode_link(old_dentry, dir, new_dentry);
          if (error)
                  return error;
  
          mutex_lock(&inode->i_mutex);
          /* Make sure we don't allow creating hardlink to an unlinked file */
          if (inode->i_nlink == 0)
                  error =  -ENOENT;
          else if (max_links && inode->i_nlink >= max_links)
                  error = -EMLINK;
          else
                  error = dir->i_op->link(old_dentry, dir, new_dentry);
          mutex_unlock(&inode->i_mutex);
          if (!error)
                  fsnotify_link(dir, inode, new_dentry);
          return error;
  }
  
  /*
   * Hardlinks are often used in delicate situations.  We avoid
   * security-related surprises by not following symlinks on the
   * newname.  --KAB
   *
   * We don't follow them on the oldname either to be compatible
   * with linux 2.0, and to avoid hard-linking to directories
   * and other special files.  --ADM
   */
  SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
                  int, newdfd, const char __user *, newname, int, flags)
  {
          struct dentry *new_dentry;
          struct path old_path, new_path;
          int how = 0;
          int error;
  
          if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
                  return -EINVAL;
          /*
           * To use null names we require CAP_DAC_READ_SEARCH
           * This ensures that not everyone will be able to create
           * handlink using the passed filedescriptor.
           */
          if (flags & AT_EMPTY_PATH) {
                  if (!capable(CAP_DAC_READ_SEARCH))
                          return -ENOENT;
                  how = LOOKUP_EMPTY;
          }
  
          if (flags & AT_SYMLINK_FOLLOW)
                  how |= LOOKUP_FOLLOW;
  retry:
          error = user_path_at(olddfd, oldname, how, &old_path);
          if (error)
                  return error;
  
          new_dentry = user_path_create(newdfd, newname, &new_path,
                                          (how & LOOKUP_REVAL));
          error = PTR_ERR(new_dentry);
          if (IS_ERR(new_dentry))
                  goto out;
  
          error = -EXDEV;
          if (old_path.mnt != new_path.mnt)
                  goto out_dput;
          error = may_linkat(&old_path);
          if (unlikely(error))
                  goto out_dput;
          error = security_path_link(old_path.dentry, &new_path, new_dentry);
          if (error)
                  goto out_dput;
          error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry);
  out_dput:
          done_path_create(&new_path, new_dentry);
          if (retry_estale(error, how)) {
                  how |= LOOKUP_REVAL;
                  goto retry;
          }
  out:
          path_put(&old_path);
  
          return error;
  }
  
  SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname)
  {
          return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
  }
  
  /*
   * The worst of all namespace operations - renaming directory. "Perverted"
   * doesn't even start to describe it. Somebody in UCB had a heck of a trip...
   * Problems:
   *      a) we can get into loop creation. Check is done in is_subdir().
   *      b) race potential - two innocent renames can create a loop together.
   *         That's where 4.4 screws up. Current fix: serialization on
   *         sb->s_vfs_rename_mutex. We might be more accurate, but that's another
   *         story.
   *      c) we have to lock _three_ objects - parents and victim (if it exists).
   *         And that - after we got ->i_mutex on parents (until then we don't know
   *         whether the target exists).  Solution: try to be smart with locking
   *         order for inodes.  We rely on the fact that tree topology may change
   *         only under ->s_vfs_rename_mutex _and_ that parent of the object we
   *         move will be locked.  Thus we can rank directories by the tree
   *         (ancestors first) and rank all non-directories after them.
   *         That works since everybody except rename does "lock parent, lookup,
   *         lock child" and rename is under ->s_vfs_rename_mutex.
   *         HOWEVER, it relies on the assumption that any object with ->lookup()
   *         has no more than 1 dentry.  If "hybrid" objects will ever appear,
   *         we'd better make sure that there's no link(2) for them.
   *      d) conversion from fhandle to dentry may come in the wrong moment - when
   *         we are removing the target. Solution: we will have to grab ->i_mutex
   *         in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on
   *         ->i_mutex on parents, which works but leads to some truly excessive
   *         locking].
   */
  static int vfs_rename_dir(struct inode *old_dir, struct dentry *old_dentry,
                            struct inode *new_dir, struct dentry *new_dentry)
  {
          int error = 0;
          struct inode *target = new_dentry->d_inode;
          unsigned max_links = new_dir->i_sb->s_max_links;
  
          /*
           * If we are going to change the parent - check write permissions,
           * we'll need to flip '..'.
           */
          if (new_dir != old_dir) {
                  error = inode_permission(old_dentry->d_inode, MAY_WRITE);
                  if (error)
                          return error;
          }
  
          error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry);
          if (error)
                  return error;
  
          dget(new_dentry);
          if (target)
                  mutex_lock(&target->i_mutex);
  
          error = -EBUSY;
          if (d_mountpoint(old_dentry) || d_mountpoint(new_dentry))
                  goto out;
  
          error = -EMLINK;
          if (max_links && !target && new_dir != old_dir &&
              new_dir->i_nlink >= max_links)
                  goto out;
  
          if (target)
                  shrink_dcache_parent(new_dentry);
          error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry);
          if (error)
                  goto out;
  
          if (target) {
                  target->i_flags |= S_DEAD;
                  dont_mount(new_dentry);
          }
  out:
          if (target)
                  mutex_unlock(&target->i_mutex);
          dput(new_dentry);
          if (!error)
                  if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE))
                          d_move(old_dentry,new_dentry);
          return error;
  }
  
  static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry,
                              struct inode *new_dir, struct dentry *new_dentry)
  {
          struct inode *target = new_dentry->d_inode;
          int error;
  
          error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry);
          if (error)
                  return error;
  
          dget(new_dentry);
          if (target)
                  mutex_lock(&target->i_mutex);
  
          error = -EBUSY;
          if (d_mountpoint(old_dentry)||d_mountpoint(new_dentry))
                  goto out;
  
          error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry);
          if (error)
                  goto out;
  
          if (target)
                  dont_mount(new_dentry);
          if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE))
                  d_move(old_dentry, new_dentry);
  out:
          if (target)
                  mutex_unlock(&target->i_mutex);
          dput(new_dentry);
          return error;
  }
  
  int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
                 struct inode *new_dir, struct dentry *new_dentry)
  {
          int error;
          int is_dir = S_ISDIR(old_dentry->d_inode->i_mode);
          const unsigned char *old_name;
  
          if (old_dentry->d_inode == new_dentry->d_inode)
                  return 0;
   
          error = may_delete(old_dir, old_dentry, is_dir);
          if (error)
                  return error;
  
          if (!new_dentry->d_inode)
                  error = may_create(new_dir, new_dentry);
          else
                  error = may_delete(new_dir, new_dentry, is_dir);
          if (error)
                  return error;
  
          if (!old_dir->i_op->rename)
                  return -EPERM;
  
          old_name = fsnotify_oldname_init(old_dentry->d_name.name);
  
          if (is_dir)
                  error = vfs_rename_dir(old_dir,old_dentry,new_dir,new_dentry);
          else
                  error = vfs_rename_other(old_dir,old_dentry,new_dir,new_dentry);
          if (!error)
                  fsnotify_move(old_dir, new_dir, old_name, is_dir,
                                new_dentry->d_inode, old_dentry);
          fsnotify_oldname_free(old_name);
  
          return error;
  }
  
  SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
                  int, newdfd, const char __user *, newname)
  {
          struct dentry *old_dir, *new_dir;
          struct dentry *old_dentry, *new_dentry;
          struct dentry *trap;
          struct nameidata oldnd, newnd;
          struct filename *from;
          struct filename *to;
          unsigned int lookup_flags = 0;
          bool should_retry = false;
          int error;
  retry:
          from = user_path_parent(olddfd, oldname, &oldnd, lookup_flags);
          if (IS_ERR(from)) {
                  error = PTR_ERR(from);
                  goto exit;
          }
  
          to = user_path_parent(newdfd, newname, &newnd, lookup_flags);
          if (IS_ERR(to)) {
                  error = PTR_ERR(to);
                  goto exit1;
          }
  
          error = -EXDEV;
          if (oldnd.path.mnt != newnd.path.mnt)
                  goto exit2;
  
          old_dir = oldnd.path.dentry;
          error = -EBUSY;
          if (oldnd.last_type != LAST_NORM)
                  goto exit2;
  
          new_dir = newnd.path.dentry;
          if (newnd.last_type != LAST_NORM)
                  goto exit2;
  
          error = mnt_want_write(oldnd.path.mnt);
          if (error)
                  goto exit2;
  
          oldnd.flags &= ~LOOKUP_PARENT;
          newnd.flags &= ~LOOKUP_PARENT;
          newnd.flags |= LOOKUP_RENAME_TARGET;
  
          trap = lock_rename(new_dir, old_dir);
  
          old_dentry = lookup_hash(&oldnd);
          error = PTR_ERR(old_dentry);
          if (IS_ERR(old_dentry))
                  goto exit3;
          /* source must exist */
          error = -ENOENT;
          if (!old_dentry->d_inode)
                  goto exit4;
          /* unless the source is a directory trailing slashes give -ENOTDIR */
          if (!S_ISDIR(old_dentry->d_inode->i_mode)) {
                  error = -ENOTDIR;
                  if (oldnd.last.name[oldnd.last.len])
                          goto exit4;
                  if (newnd.last.name[newnd.last.len])
                          goto exit4;
          }
          /* source should not be ancestor of target */
          error = -EINVAL;
          if (old_dentry == trap)
                  goto exit4;
          new_dentry = lookup_hash(&newnd);
          error = PTR_ERR(new_dentry);
          if (IS_ERR(new_dentry))
                  goto exit4;
          /* target should not be an ancestor of source */
          error = -ENOTEMPTY;
          if (new_dentry == trap)
                  goto exit5;
  
          error = security_path_rename(&oldnd.path, old_dentry,
                                       &newnd.path, new_dentry);
          if (error)
                  goto exit5;
          error = vfs_rename(old_dir->d_inode, old_dentry,
                                     new_dir->d_inode, new_dentry);
  exit5:
          dput(new_dentry);
  exit4:
          dput(old_dentry);
  exit3:
          unlock_rename(new_dir, old_dir);
          mnt_drop_write(oldnd.path.mnt);
  exit2:
          if (retry_estale(error, lookup_flags))
                  should_retry = true;
          path_put(&newnd.path);
          putname(to);
  exit1:
          path_put(&oldnd.path);
          putname(from);
          if (should_retry) {
                  should_retry = false;
                  lookup_flags |= LOOKUP_REVAL;
                  goto retry;
          }
  exit:
          return error;
  }
  
  SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newname)
  {
          return sys_renameat(AT_FDCWD, oldname, AT_FDCWD, newname);
  }
  
  int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen, const char *link)
  {
          int len;
  
          len = PTR_ERR(link);
          if (IS_ERR(link))
                  goto out;
  
          len = strlen(link);
          if (len > (unsigned) buflen)
                  len = buflen;
          if (copy_to_user(buffer, link, len))
                  len = -EFAULT;
  out:
          return len;
  }
  
  /*
   * A helper for ->readlink().  This should be used *ONLY* for symlinks that
   * have ->follow_link() touching nd only in nd_set_link().  Using (or not
   * using) it for any given inode is up to filesystem.
   */
  int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen)
  {
          struct nameidata nd;
          void *cookie;
          int res;
  
          nd.depth = 0;
          cookie = dentry->d_inode->i_op->follow_link(dentry, &nd);
          if (IS_ERR(cookie))
                  return PTR_ERR(cookie);
  
          res = vfs_readlink(dentry, buffer, buflen, nd_get_link(&nd));
          if (dentry->d_inode->i_op->put_link)
                  dentry->d_inode->i_op->put_link(dentry, &nd, cookie);
          return res;
  }
  
  int vfs_follow_link(struct nameidata *nd, const char *link)
  {
          return __vfs_follow_link(nd, link);
  }
  
  /* get the link contents into pagecache */
  static char *page_getlink(struct dentry * dentry, struct page **ppage)
  {
          char *kaddr;
          struct page *page;
          struct address_space *mapping = dentry->d_inode->i_mapping;
          page = read_mapping_page(mapping, 0, NULL);
          if (IS_ERR(page))
                  return (char*)page;
          *ppage = page;
          kaddr = kmap(page);
          nd_terminate_link(kaddr, dentry->d_inode->i_size, PAGE_SIZE - 1);
          return kaddr;
  }
  
  int page_readlink(struct dentry *dentry, char __user *buffer, int buflen)
  {
          struct page *page = NULL;
          char *s = page_getlink(dentry, &page);
          int res = vfs_readlink(dentry,buffer,buflen,s);
          if (page) {
                  kunmap(page);
                  page_cache_release(page);
          }
          return res;
  }
  
  void *page_follow_link_light(struct dentry *dentry, struct nameidata *nd)
  {
          struct page *page = NULL;
          nd_set_link(nd, page_getlink(dentry, &page));
          return page;
  }
  
  void page_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
  {
          struct page *page = cookie;
  
          if (page) {
                  kunmap(page);
                  page_cache_release(page);
          }
  }
  
  /*
   * The nofs argument instructs pagecache_write_begin to pass AOP_FLAG_NOFS
   */
  int __page_symlink(struct inode *inode, const char *symname, int len, int nofs)
  {
          struct address_space *mapping = inode->i_mapping;
          struct page *page;
          void *fsdata;
          int err;
          char *kaddr;
          unsigned int flags = AOP_FLAG_UNINTERRUPTIBLE;
          if (nofs)
                  flags |= AOP_FLAG_NOFS;
  
  retry:
          err = pagecache_write_begin(NULL, mapping, 0, len-1,
                                  flags, &page, &fsdata);
          if (err)
                  goto fail;
  
          kaddr = kmap_atomic(page);
          memcpy(kaddr, symname, len-1);
          kunmap_atomic(kaddr);
  
          err = pagecache_write_end(NULL, mapping, 0, len-1, len-1,
                                                          page, fsdata);
          if (err < 0)
                  goto fail;
          if (err < len-1)
                  goto retry;
  
          mark_inode_dirty(inode);
          return 0;
  fail:
          return err;
  }
  
  int page_symlink(struct inode *inode, const char *symname, int len)
  {
          return __page_symlink(inode, symname, len,
                          !(mapping_gfp_mask(inode->i_mapping) & __GFP_FS));
  }
  
  const struct inode_operations page_symlink_inode_operations = {
          .readlink       = generic_readlink,
          .follow_link    = page_follow_link_light,
          .put_link       = page_put_link,
  };
  
  EXPORT_SYMBOL(user_path_at);
  EXPORT_SYMBOL(follow_down_one);
  EXPORT_SYMBOL(follow_down);
  EXPORT_SYMBOL(follow_up);
  EXPORT_SYMBOL(get_write_access); /* nfsd */
  EXPORT_SYMBOL(lock_rename);
  EXPORT_SYMBOL(lookup_one_len);
  EXPORT_SYMBOL(page_follow_link_light);
  EXPORT_SYMBOL(page_put_link);
  EXPORT_SYMBOL(page_readlink);
  EXPORT_SYMBOL(__page_symlink);
  EXPORT_SYMBOL(page_symlink);
  EXPORT_SYMBOL(page_symlink_inode_operations);
  EXPORT_SYMBOL(kern_path);
  EXPORT_SYMBOL(vfs_path_lookup);
  EXPORT_SYMBOL(inode_permission);
  EXPORT_SYMBOL(unlock_rename);
  EXPORT_SYMBOL(vfs_create);
  EXPORT_SYMBOL(vfs_follow_link);
  EXPORT_SYMBOL(vfs_link);
  EXPORT_SYMBOL(vfs_mkdir);
  EXPORT_SYMBOL(vfs_mknod);
  EXPORT_SYMBOL(generic_permission);
  EXPORT_SYMBOL(vfs_readlink);
  EXPORT_SYMBOL(vfs_rename);
  EXPORT_SYMBOL(vfs_rmdir);
  EXPORT_SYMBOL(vfs_symlink);
  EXPORT_SYMBOL(vfs_unlink);
  EXPORT_SYMBOL(dentry_unhash);
  EXPORT_SYMBOL(generic_readlink);