The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*
    2  *      fs/libfs.c
    3  *      Library for filesystems writers.
    4  */
    5 
    6 #include <linux/export.h>
    7 #include <linux/pagemap.h>
    8 #include <linux/slab.h>
    9 #include <linux/mount.h>
   10 #include <linux/vfs.h>
   11 #include <linux/quotaops.h>
   12 #include <linux/mutex.h>
   13 #include <linux/exportfs.h>
   14 #include <linux/writeback.h>
   15 #include <linux/buffer_head.h> /* sync_mapping_buffers */
   16 
   17 #include <asm/uaccess.h>
   18 
   19 #include "internal.h"
   20 
   21 static inline int simple_positive(struct dentry *dentry)
   22 {
   23         return dentry->d_inode && !d_unhashed(dentry);
   24 }
   25 
   26 int simple_getattr(struct vfsmount *mnt, struct dentry *dentry,
   27                    struct kstat *stat)
   28 {
   29         struct inode *inode = dentry->d_inode;
   30         generic_fillattr(inode, stat);
   31         stat->blocks = inode->i_mapping->nrpages << (PAGE_CACHE_SHIFT - 9);
   32         return 0;
   33 }
   34 
   35 int simple_statfs(struct dentry *dentry, struct kstatfs *buf)
   36 {
   37         buf->f_type = dentry->d_sb->s_magic;
   38         buf->f_bsize = PAGE_CACHE_SIZE;
   39         buf->f_namelen = NAME_MAX;
   40         return 0;
   41 }
   42 
   43 /*
   44  * Retaining negative dentries for an in-memory filesystem just wastes
   45  * memory and lookup time: arrange for them to be deleted immediately.
   46  */
   47 static int simple_delete_dentry(const struct dentry *dentry)
   48 {
   49         return 1;
   50 }
   51 
   52 /*
   53  * Lookup the data. This is trivial - if the dentry didn't already
   54  * exist, we know it is negative.  Set d_op to delete negative dentries.
   55  */
   56 struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
   57 {
   58         static const struct dentry_operations simple_dentry_operations = {
   59                 .d_delete = simple_delete_dentry,
   60         };
   61 
   62         if (dentry->d_name.len > NAME_MAX)
   63                 return ERR_PTR(-ENAMETOOLONG);
   64         d_set_d_op(dentry, &simple_dentry_operations);
   65         d_add(dentry, NULL);
   66         return NULL;
   67 }
   68 
   69 int dcache_dir_open(struct inode *inode, struct file *file)
   70 {
   71         static struct qstr cursor_name = QSTR_INIT(".", 1);
   72 
   73         file->private_data = d_alloc(file->f_path.dentry, &cursor_name);
   74 
   75         return file->private_data ? 0 : -ENOMEM;
   76 }
   77 
   78 int dcache_dir_close(struct inode *inode, struct file *file)
   79 {
   80         dput(file->private_data);
   81         return 0;
   82 }
   83 
   84 loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
   85 {
   86         struct dentry *dentry = file->f_path.dentry;
   87         mutex_lock(&dentry->d_inode->i_mutex);
   88         switch (whence) {
   89                 case 1:
   90                         offset += file->f_pos;
   91                 case 0:
   92                         if (offset >= 0)
   93                                 break;
   94                 default:
   95                         mutex_unlock(&dentry->d_inode->i_mutex);
   96                         return -EINVAL;
   97         }
   98         if (offset != file->f_pos) {
   99                 file->f_pos = offset;
  100                 if (file->f_pos >= 2) {
  101                         struct list_head *p;
  102                         struct dentry *cursor = file->private_data;
  103                         loff_t n = file->f_pos - 2;
  104 
  105                         spin_lock(&dentry->d_lock);
  106                         /* d_lock not required for cursor */
  107                         list_del(&cursor->d_u.d_child);
  108                         p = dentry->d_subdirs.next;
  109                         while (n && p != &dentry->d_subdirs) {
  110                                 struct dentry *next;
  111                                 next = list_entry(p, struct dentry, d_u.d_child);
  112                                 spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
  113                                 if (simple_positive(next))
  114                                         n--;
  115                                 spin_unlock(&next->d_lock);
  116                                 p = p->next;
  117                         }
  118                         list_add_tail(&cursor->d_u.d_child, p);
  119                         spin_unlock(&dentry->d_lock);
  120                 }
  121         }
  122         mutex_unlock(&dentry->d_inode->i_mutex);
  123         return offset;
  124 }
  125 
  126 /* Relationship between i_mode and the DT_xxx types */
  127 static inline unsigned char dt_type(struct inode *inode)
  128 {
  129         return (inode->i_mode >> 12) & 15;
  130 }
  131 
  132 /*
  133  * Directory is locked and all positive dentries in it are safe, since
  134  * for ramfs-type trees they can't go away without unlink() or rmdir(),
  135  * both impossible due to the lock on directory.
  136  */
  137 
  138 int dcache_readdir(struct file * filp, void * dirent, filldir_t filldir)
  139 {
  140         struct dentry *dentry = filp->f_path.dentry;
  141         struct dentry *cursor = filp->private_data;
  142         struct list_head *p, *q = &cursor->d_u.d_child;
  143         ino_t ino;
  144         int i = filp->f_pos;
  145 
  146         switch (i) {
  147                 case 0:
  148                         ino = dentry->d_inode->i_ino;
  149                         if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
  150                                 break;
  151                         filp->f_pos++;
  152                         i++;
  153                         /* fallthrough */
  154                 case 1:
  155                         ino = parent_ino(dentry);
  156                         if (filldir(dirent, "..", 2, i, ino, DT_DIR) < 0)
  157                                 break;
  158                         filp->f_pos++;
  159                         i++;
  160                         /* fallthrough */
  161                 default:
  162                         spin_lock(&dentry->d_lock);
  163                         if (filp->f_pos == 2)
  164                                 list_move(q, &dentry->d_subdirs);
  165 
  166                         for (p=q->next; p != &dentry->d_subdirs; p=p->next) {
  167                                 struct dentry *next;
  168                                 next = list_entry(p, struct dentry, d_u.d_child);
  169                                 spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
  170                                 if (!simple_positive(next)) {
  171                                         spin_unlock(&next->d_lock);
  172                                         continue;
  173                                 }
  174 
  175                                 spin_unlock(&next->d_lock);
  176                                 spin_unlock(&dentry->d_lock);
  177                                 if (filldir(dirent, next->d_name.name, 
  178                                             next->d_name.len, filp->f_pos, 
  179                                             next->d_inode->i_ino, 
  180                                             dt_type(next->d_inode)) < 0)
  181                                         return 0;
  182                                 spin_lock(&dentry->d_lock);
  183                                 spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
  184                                 /* next is still alive */
  185                                 list_move(q, p);
  186                                 spin_unlock(&next->d_lock);
  187                                 p = q;
  188                                 filp->f_pos++;
  189                         }
  190                         spin_unlock(&dentry->d_lock);
  191         }
  192         return 0;
  193 }
  194 
  195 ssize_t generic_read_dir(struct file *filp, char __user *buf, size_t siz, loff_t *ppos)
  196 {
  197         return -EISDIR;
  198 }
  199 
  200 const struct file_operations simple_dir_operations = {
  201         .open           = dcache_dir_open,
  202         .release        = dcache_dir_close,
  203         .llseek         = dcache_dir_lseek,
  204         .read           = generic_read_dir,
  205         .readdir        = dcache_readdir,
  206         .fsync          = noop_fsync,
  207 };
  208 
  209 const struct inode_operations simple_dir_inode_operations = {
  210         .lookup         = simple_lookup,
  211 };
  212 
  213 static const struct super_operations simple_super_operations = {
  214         .statfs         = simple_statfs,
  215 };
  216 
  217 /*
  218  * Common helper for pseudo-filesystems (sockfs, pipefs, bdev - stuff that
  219  * will never be mountable)
  220  */
  221 struct dentry *mount_pseudo(struct file_system_type *fs_type, char *name,
  222         const struct super_operations *ops,
  223         const struct dentry_operations *dops, unsigned long magic)
  224 {
  225         struct super_block *s;
  226         struct dentry *dentry;
  227         struct inode *root;
  228         struct qstr d_name = QSTR_INIT(name, strlen(name));
  229 
  230         s = sget(fs_type, NULL, set_anon_super, MS_NOUSER, NULL);
  231         if (IS_ERR(s))
  232                 return ERR_CAST(s);
  233 
  234         s->s_maxbytes = MAX_LFS_FILESIZE;
  235         s->s_blocksize = PAGE_SIZE;
  236         s->s_blocksize_bits = PAGE_SHIFT;
  237         s->s_magic = magic;
  238         s->s_op = ops ? ops : &simple_super_operations;
  239         s->s_time_gran = 1;
  240         root = new_inode(s);
  241         if (!root)
  242                 goto Enomem;
  243         /*
  244          * since this is the first inode, make it number 1. New inodes created
  245          * after this must take care not to collide with it (by passing
  246          * max_reserved of 1 to iunique).
  247          */
  248         root->i_ino = 1;
  249         root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
  250         root->i_atime = root->i_mtime = root->i_ctime = CURRENT_TIME;
  251         dentry = __d_alloc(s, &d_name);
  252         if (!dentry) {
  253                 iput(root);
  254                 goto Enomem;
  255         }
  256         d_instantiate(dentry, root);
  257         s->s_root = dentry;
  258         s->s_d_op = dops;
  259         s->s_flags |= MS_ACTIVE;
  260         return dget(s->s_root);
  261 
  262 Enomem:
  263         deactivate_locked_super(s);
  264         return ERR_PTR(-ENOMEM);
  265 }
  266 
  267 int simple_open(struct inode *inode, struct file *file)
  268 {
  269         if (inode->i_private)
  270                 file->private_data = inode->i_private;
  271         return 0;
  272 }
  273 
  274 int simple_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
  275 {
  276         struct inode *inode = old_dentry->d_inode;
  277 
  278         inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
  279         inc_nlink(inode);
  280         ihold(inode);
  281         dget(dentry);
  282         d_instantiate(dentry, inode);
  283         return 0;
  284 }
  285 
  286 int simple_empty(struct dentry *dentry)
  287 {
  288         struct dentry *child;
  289         int ret = 0;
  290 
  291         spin_lock(&dentry->d_lock);
  292         list_for_each_entry(child, &dentry->d_subdirs, d_u.d_child) {
  293                 spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
  294                 if (simple_positive(child)) {
  295                         spin_unlock(&child->d_lock);
  296                         goto out;
  297                 }
  298                 spin_unlock(&child->d_lock);
  299         }
  300         ret = 1;
  301 out:
  302         spin_unlock(&dentry->d_lock);
  303         return ret;
  304 }
  305 
  306 int simple_unlink(struct inode *dir, struct dentry *dentry)
  307 {
  308         struct inode *inode = dentry->d_inode;
  309 
  310         inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
  311         drop_nlink(inode);
  312         dput(dentry);
  313         return 0;
  314 }
  315 
  316 int simple_rmdir(struct inode *dir, struct dentry *dentry)
  317 {
  318         if (!simple_empty(dentry))
  319                 return -ENOTEMPTY;
  320 
  321         drop_nlink(dentry->d_inode);
  322         simple_unlink(dir, dentry);
  323         drop_nlink(dir);
  324         return 0;
  325 }
  326 
  327 int simple_rename(struct inode *old_dir, struct dentry *old_dentry,
  328                 struct inode *new_dir, struct dentry *new_dentry)
  329 {
  330         struct inode *inode = old_dentry->d_inode;
  331         int they_are_dirs = S_ISDIR(old_dentry->d_inode->i_mode);
  332 
  333         if (!simple_empty(new_dentry))
  334                 return -ENOTEMPTY;
  335 
  336         if (new_dentry->d_inode) {
  337                 simple_unlink(new_dir, new_dentry);
  338                 if (they_are_dirs) {
  339                         drop_nlink(new_dentry->d_inode);
  340                         drop_nlink(old_dir);
  341                 }
  342         } else if (they_are_dirs) {
  343                 drop_nlink(old_dir);
  344                 inc_nlink(new_dir);
  345         }
  346 
  347         old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
  348                 new_dir->i_mtime = inode->i_ctime = CURRENT_TIME;
  349 
  350         return 0;
  351 }
  352 
  353 /**
  354  * simple_setattr - setattr for simple filesystem
  355  * @dentry: dentry
  356  * @iattr: iattr structure
  357  *
  358  * Returns 0 on success, -error on failure.
  359  *
  360  * simple_setattr is a simple ->setattr implementation without a proper
  361  * implementation of size changes.
  362  *
  363  * It can either be used for in-memory filesystems or special files
  364  * on simple regular filesystems.  Anything that needs to change on-disk
  365  * or wire state on size changes needs its own setattr method.
  366  */
  367 int simple_setattr(struct dentry *dentry, struct iattr *iattr)
  368 {
  369         struct inode *inode = dentry->d_inode;
  370         int error;
  371 
  372         error = inode_change_ok(inode, iattr);
  373         if (error)
  374                 return error;
  375 
  376         if (iattr->ia_valid & ATTR_SIZE)
  377                 truncate_setsize(inode, iattr->ia_size);
  378         setattr_copy(inode, iattr);
  379         mark_inode_dirty(inode);
  380         return 0;
  381 }
  382 EXPORT_SYMBOL(simple_setattr);
  383 
  384 int simple_readpage(struct file *file, struct page *page)
  385 {
  386         clear_highpage(page);
  387         flush_dcache_page(page);
  388         SetPageUptodate(page);
  389         unlock_page(page);
  390         return 0;
  391 }
  392 
  393 int simple_write_begin(struct file *file, struct address_space *mapping,
  394                         loff_t pos, unsigned len, unsigned flags,
  395                         struct page **pagep, void **fsdata)
  396 {
  397         struct page *page;
  398         pgoff_t index;
  399 
  400         index = pos >> PAGE_CACHE_SHIFT;
  401 
  402         page = grab_cache_page_write_begin(mapping, index, flags);
  403         if (!page)
  404                 return -ENOMEM;
  405 
  406         *pagep = page;
  407 
  408         if (!PageUptodate(page) && (len != PAGE_CACHE_SIZE)) {
  409                 unsigned from = pos & (PAGE_CACHE_SIZE - 1);
  410 
  411                 zero_user_segments(page, 0, from, from + len, PAGE_CACHE_SIZE);
  412         }
  413         return 0;
  414 }
  415 
  416 /**
  417  * simple_write_end - .write_end helper for non-block-device FSes
  418  * @available: See .write_end of address_space_operations
  419  * @file:               "
  420  * @mapping:            "
  421  * @pos:                "
  422  * @len:                "
  423  * @copied:             "
  424  * @page:               "
  425  * @fsdata:             "
  426  *
  427  * simple_write_end does the minimum needed for updating a page after writing is
  428  * done. It has the same API signature as the .write_end of
  429  * address_space_operations vector. So it can just be set onto .write_end for
  430  * FSes that don't need any other processing. i_mutex is assumed to be held.
  431  * Block based filesystems should use generic_write_end().
  432  * NOTE: Even though i_size might get updated by this function, mark_inode_dirty
  433  * is not called, so a filesystem that actually does store data in .write_inode
  434  * should extend on what's done here with a call to mark_inode_dirty() in the
  435  * case that i_size has changed.
  436  */
  437 int simple_write_end(struct file *file, struct address_space *mapping,
  438                         loff_t pos, unsigned len, unsigned copied,
  439                         struct page *page, void *fsdata)
  440 {
  441         struct inode *inode = page->mapping->host;
  442         loff_t last_pos = pos + copied;
  443 
  444         /* zero the stale part of the page if we did a short copy */
  445         if (copied < len) {
  446                 unsigned from = pos & (PAGE_CACHE_SIZE - 1);
  447 
  448                 zero_user(page, from + copied, len - copied);
  449         }
  450 
  451         if (!PageUptodate(page))
  452                 SetPageUptodate(page);
  453         /*
  454          * No need to use i_size_read() here, the i_size
  455          * cannot change under us because we hold the i_mutex.
  456          */
  457         if (last_pos > inode->i_size)
  458                 i_size_write(inode, last_pos);
  459 
  460         set_page_dirty(page);
  461         unlock_page(page);
  462         page_cache_release(page);
  463 
  464         return copied;
  465 }
  466 
  467 /*
  468  * the inodes created here are not hashed. If you use iunique to generate
  469  * unique inode values later for this filesystem, then you must take care
  470  * to pass it an appropriate max_reserved value to avoid collisions.
  471  */
  472 int simple_fill_super(struct super_block *s, unsigned long magic,
  473                       struct tree_descr *files)
  474 {
  475         struct inode *inode;
  476         struct dentry *root;
  477         struct dentry *dentry;
  478         int i;
  479 
  480         s->s_blocksize = PAGE_CACHE_SIZE;
  481         s->s_blocksize_bits = PAGE_CACHE_SHIFT;
  482         s->s_magic = magic;
  483         s->s_op = &simple_super_operations;
  484         s->s_time_gran = 1;
  485 
  486         inode = new_inode(s);
  487         if (!inode)
  488                 return -ENOMEM;
  489         /*
  490          * because the root inode is 1, the files array must not contain an
  491          * entry at index 1
  492          */
  493         inode->i_ino = 1;
  494         inode->i_mode = S_IFDIR | 0755;
  495         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
  496         inode->i_op = &simple_dir_inode_operations;
  497         inode->i_fop = &simple_dir_operations;
  498         set_nlink(inode, 2);
  499         root = d_make_root(inode);
  500         if (!root)
  501                 return -ENOMEM;
  502         for (i = 0; !files->name || files->name[0]; i++, files++) {
  503                 if (!files->name)
  504                         continue;
  505 
  506                 /* warn if it tries to conflict with the root inode */
  507                 if (unlikely(i == 1))
  508                         printk(KERN_WARNING "%s: %s passed in a files array"
  509                                 "with an index of 1!\n", __func__,
  510                                 s->s_type->name);
  511 
  512                 dentry = d_alloc_name(root, files->name);
  513                 if (!dentry)
  514                         goto out;
  515                 inode = new_inode(s);
  516                 if (!inode) {
  517                         dput(dentry);
  518                         goto out;
  519                 }
  520                 inode->i_mode = S_IFREG | files->mode;
  521                 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
  522                 inode->i_fop = files->ops;
  523                 inode->i_ino = i;
  524                 d_add(dentry, inode);
  525         }
  526         s->s_root = root;
  527         return 0;
  528 out:
  529         d_genocide(root);
  530         shrink_dcache_parent(root);
  531         dput(root);
  532         return -ENOMEM;
  533 }
  534 
  535 static DEFINE_SPINLOCK(pin_fs_lock);
  536 
  537 int simple_pin_fs(struct file_system_type *type, struct vfsmount **mount, int *count)
  538 {
  539         struct vfsmount *mnt = NULL;
  540         spin_lock(&pin_fs_lock);
  541         if (unlikely(!*mount)) {
  542                 spin_unlock(&pin_fs_lock);
  543                 mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, NULL);
  544                 if (IS_ERR(mnt))
  545                         return PTR_ERR(mnt);
  546                 spin_lock(&pin_fs_lock);
  547                 if (!*mount)
  548                         *mount = mnt;
  549         }
  550         mntget(*mount);
  551         ++*count;
  552         spin_unlock(&pin_fs_lock);
  553         mntput(mnt);
  554         return 0;
  555 }
  556 
  557 void simple_release_fs(struct vfsmount **mount, int *count)
  558 {
  559         struct vfsmount *mnt;
  560         spin_lock(&pin_fs_lock);
  561         mnt = *mount;
  562         if (!--*count)
  563                 *mount = NULL;
  564         spin_unlock(&pin_fs_lock);
  565         mntput(mnt);
  566 }
  567 
  568 /**
  569  * simple_read_from_buffer - copy data from the buffer to user space
  570  * @to: the user space buffer to read to
  571  * @count: the maximum number of bytes to read
  572  * @ppos: the current position in the buffer
  573  * @from: the buffer to read from
  574  * @available: the size of the buffer
  575  *
  576  * The simple_read_from_buffer() function reads up to @count bytes from the
  577  * buffer @from at offset @ppos into the user space address starting at @to.
  578  *
  579  * On success, the number of bytes read is returned and the offset @ppos is
  580  * advanced by this number, or negative value is returned on error.
  581  **/
  582 ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
  583                                 const void *from, size_t available)
  584 {
  585         loff_t pos = *ppos;
  586         size_t ret;
  587 
  588         if (pos < 0)
  589                 return -EINVAL;
  590         if (pos >= available || !count)
  591                 return 0;
  592         if (count > available - pos)
  593                 count = available - pos;
  594         ret = copy_to_user(to, from + pos, count);
  595         if (ret == count)
  596                 return -EFAULT;
  597         count -= ret;
  598         *ppos = pos + count;
  599         return count;
  600 }
  601 
  602 /**
  603  * simple_write_to_buffer - copy data from user space to the buffer
  604  * @to: the buffer to write to
  605  * @available: the size of the buffer
  606  * @ppos: the current position in the buffer
  607  * @from: the user space buffer to read from
  608  * @count: the maximum number of bytes to read
  609  *
  610  * The simple_write_to_buffer() function reads up to @count bytes from the user
  611  * space address starting at @from into the buffer @to at offset @ppos.
  612  *
  613  * On success, the number of bytes written is returned and the offset @ppos is
  614  * advanced by this number, or negative value is returned on error.
  615  **/
  616 ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
  617                 const void __user *from, size_t count)
  618 {
  619         loff_t pos = *ppos;
  620         size_t res;
  621 
  622         if (pos < 0)
  623                 return -EINVAL;
  624         if (pos >= available || !count)
  625                 return 0;
  626         if (count > available - pos)
  627                 count = available - pos;
  628         res = copy_from_user(to + pos, from, count);
  629         if (res == count)
  630                 return -EFAULT;
  631         count -= res;
  632         *ppos = pos + count;
  633         return count;
  634 }
  635 
  636 /**
  637  * memory_read_from_buffer - copy data from the buffer
  638  * @to: the kernel space buffer to read to
  639  * @count: the maximum number of bytes to read
  640  * @ppos: the current position in the buffer
  641  * @from: the buffer to read from
  642  * @available: the size of the buffer
  643  *
  644  * The memory_read_from_buffer() function reads up to @count bytes from the
  645  * buffer @from at offset @ppos into the kernel space address starting at @to.
  646  *
  647  * On success, the number of bytes read is returned and the offset @ppos is
  648  * advanced by this number, or negative value is returned on error.
  649  **/
  650 ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
  651                                 const void *from, size_t available)
  652 {
  653         loff_t pos = *ppos;
  654 
  655         if (pos < 0)
  656                 return -EINVAL;
  657         if (pos >= available)
  658                 return 0;
  659         if (count > available - pos)
  660                 count = available - pos;
  661         memcpy(to, from + pos, count);
  662         *ppos = pos + count;
  663 
  664         return count;
  665 }
  666 
  667 /*
  668  * Transaction based IO.
  669  * The file expects a single write which triggers the transaction, and then
  670  * possibly a read which collects the result - which is stored in a
  671  * file-local buffer.
  672  */
  673 
  674 void simple_transaction_set(struct file *file, size_t n)
  675 {
  676         struct simple_transaction_argresp *ar = file->private_data;
  677 
  678         BUG_ON(n > SIMPLE_TRANSACTION_LIMIT);
  679 
  680         /*
  681          * The barrier ensures that ar->size will really remain zero until
  682          * ar->data is ready for reading.
  683          */
  684         smp_mb();
  685         ar->size = n;
  686 }
  687 
  688 char *simple_transaction_get(struct file *file, const char __user *buf, size_t size)
  689 {
  690         struct simple_transaction_argresp *ar;
  691         static DEFINE_SPINLOCK(simple_transaction_lock);
  692 
  693         if (size > SIMPLE_TRANSACTION_LIMIT - 1)
  694                 return ERR_PTR(-EFBIG);
  695 
  696         ar = (struct simple_transaction_argresp *)get_zeroed_page(GFP_KERNEL);
  697         if (!ar)
  698                 return ERR_PTR(-ENOMEM);
  699 
  700         spin_lock(&simple_transaction_lock);
  701 
  702         /* only one write allowed per open */
  703         if (file->private_data) {
  704                 spin_unlock(&simple_transaction_lock);
  705                 free_page((unsigned long)ar);
  706                 return ERR_PTR(-EBUSY);
  707         }
  708 
  709         file->private_data = ar;
  710 
  711         spin_unlock(&simple_transaction_lock);
  712 
  713         if (copy_from_user(ar->data, buf, size))
  714                 return ERR_PTR(-EFAULT);
  715 
  716         return ar->data;
  717 }
  718 
  719 ssize_t simple_transaction_read(struct file *file, char __user *buf, size_t size, loff_t *pos)
  720 {
  721         struct simple_transaction_argresp *ar = file->private_data;
  722 
  723         if (!ar)
  724                 return 0;
  725         return simple_read_from_buffer(buf, size, pos, ar->data, ar->size);
  726 }
  727 
  728 int simple_transaction_release(struct inode *inode, struct file *file)
  729 {
  730         free_page((unsigned long)file->private_data);
  731         return 0;
  732 }
  733 
  734 /* Simple attribute files */
  735 
  736 struct simple_attr {
  737         int (*get)(void *, u64 *);
  738         int (*set)(void *, u64);
  739         char get_buf[24];       /* enough to store a u64 and "\n\0" */
  740         char set_buf[24];
  741         void *data;
  742         const char *fmt;        /* format for read operation */
  743         struct mutex mutex;     /* protects access to these buffers */
  744 };
  745 
  746 /* simple_attr_open is called by an actual attribute open file operation
  747  * to set the attribute specific access operations. */
  748 int simple_attr_open(struct inode *inode, struct file *file,
  749                      int (*get)(void *, u64 *), int (*set)(void *, u64),
  750                      const char *fmt)
  751 {
  752         struct simple_attr *attr;
  753 
  754         attr = kmalloc(sizeof(*attr), GFP_KERNEL);
  755         if (!attr)
  756                 return -ENOMEM;
  757 
  758         attr->get = get;
  759         attr->set = set;
  760         attr->data = inode->i_private;
  761         attr->fmt = fmt;
  762         mutex_init(&attr->mutex);
  763 
  764         file->private_data = attr;
  765 
  766         return nonseekable_open(inode, file);
  767 }
  768 
  769 int simple_attr_release(struct inode *inode, struct file *file)
  770 {
  771         kfree(file->private_data);
  772         return 0;
  773 }
  774 
  775 /* read from the buffer that is filled with the get function */
  776 ssize_t simple_attr_read(struct file *file, char __user *buf,
  777                          size_t len, loff_t *ppos)
  778 {
  779         struct simple_attr *attr;
  780         size_t size;
  781         ssize_t ret;
  782 
  783         attr = file->private_data;
  784 
  785         if (!attr->get)
  786                 return -EACCES;
  787 
  788         ret = mutex_lock_interruptible(&attr->mutex);
  789         if (ret)
  790                 return ret;
  791 
  792         if (*ppos) {            /* continued read */
  793                 size = strlen(attr->get_buf);
  794         } else {                /* first read */
  795                 u64 val;
  796                 ret = attr->get(attr->data, &val);
  797                 if (ret)
  798                         goto out;
  799 
  800                 size = scnprintf(attr->get_buf, sizeof(attr->get_buf),
  801                                  attr->fmt, (unsigned long long)val);
  802         }
  803 
  804         ret = simple_read_from_buffer(buf, len, ppos, attr->get_buf, size);
  805 out:
  806         mutex_unlock(&attr->mutex);
  807         return ret;
  808 }
  809 
  810 /* interpret the buffer as a number to call the set function with */
  811 ssize_t simple_attr_write(struct file *file, const char __user *buf,
  812                           size_t len, loff_t *ppos)
  813 {
  814         struct simple_attr *attr;
  815         u64 val;
  816         size_t size;
  817         ssize_t ret;
  818 
  819         attr = file->private_data;
  820         if (!attr->set)
  821                 return -EACCES;
  822 
  823         ret = mutex_lock_interruptible(&attr->mutex);
  824         if (ret)
  825                 return ret;
  826 
  827         ret = -EFAULT;
  828         size = min(sizeof(attr->set_buf) - 1, len);
  829         if (copy_from_user(attr->set_buf, buf, size))
  830                 goto out;
  831 
  832         attr->set_buf[size] = '\0';
  833         val = simple_strtoll(attr->set_buf, NULL, 0);
  834         ret = attr->set(attr->data, val);
  835         if (ret == 0)
  836                 ret = len; /* on success, claim we got the whole input */
  837 out:
  838         mutex_unlock(&attr->mutex);
  839         return ret;
  840 }
  841 
  842 /**
  843  * generic_fh_to_dentry - generic helper for the fh_to_dentry export operation
  844  * @sb:         filesystem to do the file handle conversion on
  845  * @fid:        file handle to convert
  846  * @fh_len:     length of the file handle in bytes
  847  * @fh_type:    type of file handle
  848  * @get_inode:  filesystem callback to retrieve inode
  849  *
  850  * This function decodes @fid as long as it has one of the well-known
  851  * Linux filehandle types and calls @get_inode on it to retrieve the
  852  * inode for the object specified in the file handle.
  853  */
  854 struct dentry *generic_fh_to_dentry(struct super_block *sb, struct fid *fid,
  855                 int fh_len, int fh_type, struct inode *(*get_inode)
  856                         (struct super_block *sb, u64 ino, u32 gen))
  857 {
  858         struct inode *inode = NULL;
  859 
  860         if (fh_len < 2)
  861                 return NULL;
  862 
  863         switch (fh_type) {
  864         case FILEID_INO32_GEN:
  865         case FILEID_INO32_GEN_PARENT:
  866                 inode = get_inode(sb, fid->i32.ino, fid->i32.gen);
  867                 break;
  868         }
  869 
  870         return d_obtain_alias(inode);
  871 }
  872 EXPORT_SYMBOL_GPL(generic_fh_to_dentry);
  873 
  874 /**
  875  * generic_fh_to_parent - generic helper for the fh_to_parent export operation
  876  * @sb:         filesystem to do the file handle conversion on
  877  * @fid:        file handle to convert
  878  * @fh_len:     length of the file handle in bytes
  879  * @fh_type:    type of file handle
  880  * @get_inode:  filesystem callback to retrieve inode
  881  *
  882  * This function decodes @fid as long as it has one of the well-known
  883  * Linux filehandle types and calls @get_inode on it to retrieve the
  884  * inode for the _parent_ object specified in the file handle if it
  885  * is specified in the file handle, or NULL otherwise.
  886  */
  887 struct dentry *generic_fh_to_parent(struct super_block *sb, struct fid *fid,
  888                 int fh_len, int fh_type, struct inode *(*get_inode)
  889                         (struct super_block *sb, u64 ino, u32 gen))
  890 {
  891         struct inode *inode = NULL;
  892 
  893         if (fh_len <= 2)
  894                 return NULL;
  895 
  896         switch (fh_type) {
  897         case FILEID_INO32_GEN_PARENT:
  898                 inode = get_inode(sb, fid->i32.parent_ino,
  899                                   (fh_len > 3 ? fid->i32.parent_gen : 0));
  900                 break;
  901         }
  902 
  903         return d_obtain_alias(inode);
  904 }
  905 EXPORT_SYMBOL_GPL(generic_fh_to_parent);
  906 
  907 /**
  908  * generic_file_fsync - generic fsync implementation for simple filesystems
  909  * @file:       file to synchronize
  910  * @datasync:   only synchronize essential metadata if true
  911  *
  912  * This is a generic implementation of the fsync method for simple
  913  * filesystems which track all non-inode metadata in the buffers list
  914  * hanging off the address_space structure.
  915  */
  916 int generic_file_fsync(struct file *file, loff_t start, loff_t end,
  917                        int datasync)
  918 {
  919         struct inode *inode = file->f_mapping->host;
  920         int err;
  921         int ret;
  922 
  923         err = filemap_write_and_wait_range(inode->i_mapping, start, end);
  924         if (err)
  925                 return err;
  926 
  927         mutex_lock(&inode->i_mutex);
  928         ret = sync_mapping_buffers(inode->i_mapping);
  929         if (!(inode->i_state & I_DIRTY))
  930                 goto out;
  931         if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
  932                 goto out;
  933 
  934         err = sync_inode_metadata(inode, 1);
  935         if (ret == 0)
  936                 ret = err;
  937 out:
  938         mutex_unlock(&inode->i_mutex);
  939         return ret;
  940 }
  941 EXPORT_SYMBOL(generic_file_fsync);
  942 
  943 /**
  944  * generic_check_addressable - Check addressability of file system
  945  * @blocksize_bits:     log of file system block size
  946  * @num_blocks:         number of blocks in file system
  947  *
  948  * Determine whether a file system with @num_blocks blocks (and a
  949  * block size of 2**@blocksize_bits) is addressable by the sector_t
  950  * and page cache of the system.  Return 0 if so and -EFBIG otherwise.
  951  */
  952 int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
  953 {
  954         u64 last_fs_block = num_blocks - 1;
  955         u64 last_fs_page =
  956                 last_fs_block >> (PAGE_CACHE_SHIFT - blocksize_bits);
  957 
  958         if (unlikely(num_blocks == 0))
  959                 return 0;
  960 
  961         if ((blocksize_bits < 9) || (blocksize_bits > PAGE_CACHE_SHIFT))
  962                 return -EINVAL;
  963 
  964         if ((last_fs_block > (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
  965             (last_fs_page > (pgoff_t)(~0ULL))) {
  966                 return -EFBIG;
  967         }
  968         return 0;
  969 }
  970 EXPORT_SYMBOL(generic_check_addressable);
  971 
  972 /*
  973  * No-op implementation of ->fsync for in-memory filesystems.
  974  */
  975 int noop_fsync(struct file *file, loff_t start, loff_t end, int datasync)
  976 {
  977         return 0;
  978 }
  979 
  980 EXPORT_SYMBOL(dcache_dir_close);
  981 EXPORT_SYMBOL(dcache_dir_lseek);
  982 EXPORT_SYMBOL(dcache_dir_open);
  983 EXPORT_SYMBOL(dcache_readdir);
  984 EXPORT_SYMBOL(generic_read_dir);
  985 EXPORT_SYMBOL(mount_pseudo);
  986 EXPORT_SYMBOL(simple_write_begin);
  987 EXPORT_SYMBOL(simple_write_end);
  988 EXPORT_SYMBOL(simple_dir_inode_operations);
  989 EXPORT_SYMBOL(simple_dir_operations);
  990 EXPORT_SYMBOL(simple_empty);
  991 EXPORT_SYMBOL(simple_fill_super);
  992 EXPORT_SYMBOL(simple_getattr);
  993 EXPORT_SYMBOL(simple_open);
  994 EXPORT_SYMBOL(simple_link);
  995 EXPORT_SYMBOL(simple_lookup);
  996 EXPORT_SYMBOL(simple_pin_fs);
  997 EXPORT_SYMBOL(simple_readpage);
  998 EXPORT_SYMBOL(simple_release_fs);
  999 EXPORT_SYMBOL(simple_rename);
 1000 EXPORT_SYMBOL(simple_rmdir);
 1001 EXPORT_SYMBOL(simple_statfs);
 1002 EXPORT_SYMBOL(noop_fsync);
 1003 EXPORT_SYMBOL(simple_unlink);
 1004 EXPORT_SYMBOL(simple_read_from_buffer);
 1005 EXPORT_SYMBOL(simple_write_to_buffer);
 1006 EXPORT_SYMBOL(memory_read_from_buffer);
 1007 EXPORT_SYMBOL(simple_transaction_set);
 1008 EXPORT_SYMBOL(simple_transaction_get);
 1009 EXPORT_SYMBOL(simple_transaction_read);
 1010 EXPORT_SYMBOL(simple_transaction_release);
 1011 EXPORT_SYMBOL_GPL(simple_attr_open);
 1012 EXPORT_SYMBOL_GPL(simple_attr_release);
 1013 EXPORT_SYMBOL_GPL(simple_attr_read);
 1014 EXPORT_SYMBOL_GPL(simple_attr_write);

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