FreeBSD/Linux Kernel Cross Reference
sys/kern/vfs_nlookup.c

     /*
      * Copyright (c) 2004 The DragonFly Project.  All rights reserved.
      * 
      * This code is derived from software contributed to The DragonFly Project
      * by Matthew Dillon <dillon@backplane.com>
      * 
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
     * 
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in
     *    the documentation and/or other materials provided with the
     *    distribution.
     * 3. Neither the name of The DragonFly Project nor the names of its
     *    contributors may be used to endorse or promote products derived
     *    from this software without specific, prior written permission.
     * 
     * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
     * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
     * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
     * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
     * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
     * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
     * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
     * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    /*
     * nlookup() is the 'new' namei interface.  Rather then return directory and
     * leaf vnodes (in various lock states) the new interface instead deals in
     * namecache records.  Namecache records may represent both a positive or
     * a negative hit.  The namespace is locked via the namecache record instead
     * of via the vnode, and only the leaf namecache record (representing the
     * filename) needs to be locked.
     *
     * This greatly improves filesystem parallelism and is a huge simplification
     * of the API verses the old vnode locking / namei scheme.
     *
     * Filesystems must actively control the caching aspects of the namecache,
     * and since namecache pointers are used as handles they are non-optional
     * even for filesystems which do not generally wish to cache things.  It is
     * intended that a separate cache coherency API will be constructed to handle
     * these issues.
     */
    
    #include "opt_ktrace.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/vnode.h>
    #include <sys/mount.h>
    #include <sys/filedesc.h>
    #include <sys/proc.h>
    #include <sys/namei.h>
    #include <sys/nlookup.h>
    #include <sys/malloc.h>
    #include <sys/stat.h>
    #include <sys/objcache.h>
    #include <sys/file.h>
    
    #ifdef KTRACE
    #include <sys/ktrace.h>
    #endif
    
    static int naccess(struct nchandle *nch, int vmode, struct ucred *cred,
                    int *stickyp);
    
    /*
     * Initialize a nlookup() structure, early error return for copyin faults
     * or a degenerate empty string (which is not allowed).
     *
     * The first process proc0's credentials are used if the calling thread
     * is not associated with a process context.
     *
     * MPSAFE
     */
    int
    nlookup_init(struct nlookupdata *nd, 
                 const char *path, enum uio_seg seg, int flags)
    {
        size_t pathlen;
        struct proc *p;
        thread_t td;
        int error;
    
        td = curthread;
        p = td->td_proc;
    
        /*
         * note: the pathlen set by copy*str() includes the terminating \0.
         */
        bzero(nd, sizeof(struct nlookupdata));
       nd->nl_path = objcache_get(namei_oc, M_WAITOK);
       nd->nl_flags |= NLC_HASBUF;
       if (seg == UIO_SYSSPACE) 
           error = copystr(path, nd->nl_path, MAXPATHLEN, &pathlen);
       else
           error = copyinstr(path, nd->nl_path, MAXPATHLEN, &pathlen);
   
       /*
        * Don't allow empty pathnames.
        * POSIX.1 requirement: "" is not a vaild file name.
        */
       if (error == 0 && pathlen <= 1)
           error = ENOENT;
   
       if (error == 0) {
           if (p && p->p_fd) {
               cache_copy(&p->p_fd->fd_ncdir, &nd->nl_nch);
               cache_copy(&p->p_fd->fd_nrdir, &nd->nl_rootnch);
               if (p->p_fd->fd_njdir.ncp)
                   cache_copy(&p->p_fd->fd_njdir, &nd->nl_jailnch);
               nd->nl_cred = crhold(p->p_ucred);
           } else {
               cache_copy(&rootnch, &nd->nl_nch);
               cache_copy(&nd->nl_nch, &nd->nl_rootnch);
               cache_copy(&nd->nl_nch, &nd->nl_jailnch);
               nd->nl_cred = crhold(proc0.p_ucred);
           }
           nd->nl_td = td;
           nd->nl_flags |= flags;
       } else {
           nlookup_done(nd);
       }
       return(error);
   }
   
   
   /*
    * nlookup_init() for "at" family of syscalls.
    *
    * Works similarly to nlookup_init() but if path is relative and fd is not
    * AT_FDCWD, path is interpreted relative to the directory pointed to by fd.
    * In this case, the file entry pointed to by fd is ref'ed and returned in
    * *fpp. 
    *
    * If the call succeeds, nlookup_done_at() must be called to clean-up the nd
    * and release the ref to the file entry.
    */
   int
   nlookup_init_at(struct nlookupdata *nd, struct file **fpp, int fd, 
                   const char *path, enum uio_seg seg, int flags)
   {
           struct thread *td = curthread;
           struct proc *p = td->td_proc;
           struct file* fp;
           struct vnode *vp;
           int error;
   
           *fpp = NULL;
   
           if  ((error = nlookup_init(nd, path, seg, flags)) != 0) {
                   return (error);
           }
   
           if (nd->nl_path[0] != '/' && fd != AT_FDCWD) {
                   if ((error = holdvnode(p->p_fd, fd, &fp)) != 0)
                           goto done;
                   vp = (struct vnode*)fp->f_data;
                   if (vp->v_type != VDIR || fp->f_nchandle.ncp == NULL) {
                           fdrop(fp);
                           fp = NULL;
                           error = ENOTDIR;
                           goto done;
                   }
                   cache_drop(&nd->nl_nch);
                   cache_copy(&fp->f_nchandle, &nd->nl_nch);
                   *fpp = fp;
           }
   
   
   done:
           if (error)
                   nlookup_done(nd);
           return (error);
   
   }
   
   /*
    * This works similarly to nlookup_init() but does not assume a process
    * context.  rootnch is always chosen for the root directory and the cred
    * and starting directory are supplied in arguments.
    */
   int
   nlookup_init_raw(struct nlookupdata *nd, 
                const char *path, enum uio_seg seg, int flags,
                struct ucred *cred, struct nchandle *ncstart)
   {
       size_t pathlen;
       thread_t td;
       int error;
   
       td = curthread;
   
       bzero(nd, sizeof(struct nlookupdata));
       nd->nl_path = objcache_get(namei_oc, M_WAITOK);
       nd->nl_flags |= NLC_HASBUF;
       if (seg == UIO_SYSSPACE) 
           error = copystr(path, nd->nl_path, MAXPATHLEN, &pathlen);
       else
           error = copyinstr(path, nd->nl_path, MAXPATHLEN, &pathlen);
   
       /*
        * Don't allow empty pathnames.
        * POSIX.1 requirement: "" is not a vaild file name.
        */
       if (error == 0 && pathlen <= 1)
           error = ENOENT;
   
       if (error == 0) {
           cache_copy(ncstart, &nd->nl_nch);
           cache_copy(&rootnch, &nd->nl_rootnch);
           cache_copy(&rootnch, &nd->nl_jailnch);
           nd->nl_cred = crhold(cred);
           nd->nl_td = td;
           nd->nl_flags |= flags;
       } else {
           nlookup_done(nd);
       }
       return(error);
   }
   
   /*
    * This works similarly to nlookup_init_raw() but does not rely
    * on rootnch being initialized yet.
    */
   int
   nlookup_init_root(struct nlookupdata *nd, 
                const char *path, enum uio_seg seg, int flags,
                struct ucred *cred, struct nchandle *ncstart,
                struct nchandle *ncroot)
   {
       size_t pathlen;
       thread_t td;
       int error;
   
       td = curthread;
   
       bzero(nd, sizeof(struct nlookupdata));
       nd->nl_path = objcache_get(namei_oc, M_WAITOK);
       nd->nl_flags |= NLC_HASBUF;
       if (seg == UIO_SYSSPACE) 
           error = copystr(path, nd->nl_path, MAXPATHLEN, &pathlen);
       else
           error = copyinstr(path, nd->nl_path, MAXPATHLEN, &pathlen);
   
       /*
        * Don't allow empty pathnames.
        * POSIX.1 requirement: "" is not a vaild file name.
        */
       if (error == 0 && pathlen <= 1)
           error = ENOENT;
   
       if (error == 0) {
           cache_copy(ncstart, &nd->nl_nch);
           cache_copy(ncroot, &nd->nl_rootnch);
           cache_copy(ncroot, &nd->nl_jailnch);
           nd->nl_cred = crhold(cred);
           nd->nl_td = td;
           nd->nl_flags |= flags;
       } else {
           nlookup_done(nd);
       }
       return(error);
   }
   
   /*
    * Set a different credential; this credential will be used by future
    * operations performed on nd.nl_open_vp and nlookupdata structure.
    */
   void
   nlookup_set_cred(struct nlookupdata *nd, struct ucred *cred)
   {
           KKASSERT(nd->nl_cred != NULL);
   
           if (nd->nl_cred != cred) {
                   cred = crhold(cred);
                   crfree(nd->nl_cred);
                   nd->nl_cred = cred;
           }
   }
   
   /*
    * Cleanup a nlookupdata structure after we are through with it.  This may
    * be called on any nlookupdata structure initialized with nlookup_init().
    * Calling nlookup_done() is mandatory in all cases except where nlookup_init()
    * returns an error, even if as a consumer you believe you have taken all
    * dynamic elements out of the nlookupdata structure.
    */
   void
   nlookup_done(struct nlookupdata *nd)
   {
       if (nd->nl_nch.ncp) {
           if (nd->nl_flags & NLC_NCPISLOCKED) {
               nd->nl_flags &= ~NLC_NCPISLOCKED;
               cache_unlock(&nd->nl_nch);
           }
           cache_drop(&nd->nl_nch);        /* NULL's out the nch */
       }
       if (nd->nl_rootnch.ncp)
           cache_drop(&nd->nl_rootnch);
       if (nd->nl_jailnch.ncp)
           cache_drop(&nd->nl_jailnch);
       if ((nd->nl_flags & NLC_HASBUF) && nd->nl_path) {
           objcache_put(namei_oc, nd->nl_path);
           nd->nl_path = NULL;
       }
       if (nd->nl_cred) {
           crfree(nd->nl_cred);
           nd->nl_cred = NULL;
       }
       if (nd->nl_open_vp) {
           if (nd->nl_flags & NLC_LOCKVP) {
                   vn_unlock(nd->nl_open_vp);
                   nd->nl_flags &= ~NLC_LOCKVP;
           }
           vn_close(nd->nl_open_vp, nd->nl_vp_fmode);
           nd->nl_open_vp = NULL;
       }
       if (nd->nl_dvp) {
           vrele(nd->nl_dvp);
           nd->nl_dvp = NULL;
       }
       nd->nl_flags = 0;   /* clear remaining flags (just clear everything) */
   }
   
   /*
    * Works similarly to nlookup_done() when nd initialized with
    * nlookup_init_at().
    */
   void
   nlookup_done_at(struct nlookupdata *nd, struct file *fp)
   {
           nlookup_done(nd);
           if (fp != NULL)
                   fdrop(fp);
   }
   
   void
   nlookup_zero(struct nlookupdata *nd)
   {
           bzero(nd, sizeof(struct nlookupdata));
   }
   
   /*
    * Simple all-in-one nlookup.  Returns a locked namecache structure or NULL
    * if an error occured. 
    *
    * Note that the returned ncp is not checked for permissions, though VEXEC
    * is checked on the directory path leading up to the result.  The caller
    * must call naccess() to check the permissions of the returned leaf.
    */
   struct nchandle
   nlookup_simple(const char *str, enum uio_seg seg,
                  int niflags, int *error)
   {
       struct nlookupdata nd;
       struct nchandle nch;
   
       *error = nlookup_init(&nd, str, seg, niflags);
       if (*error == 0) {
               if ((*error = nlookup(&nd)) == 0) {
                       nch = nd.nl_nch;    /* keep hold ref from structure */
                       cache_zero(&nd.nl_nch); /* and NULL out */
               } else {
                       cache_zero(&nch);
               }
               nlookup_done(&nd);
       } else {
               cache_zero(&nch);
       }
       return(nch);
   }
   
   /*
    * Returns non-zero if the path element is the last element
    */
   static
   int
   islastelement(const char *ptr)
   {
           while (*ptr == '/')
                   ++ptr;
           return (*ptr == 0);
   }
   
   /*
    * Returns non-zero if we need to lock the namecache element
    * exclusively.  Unless otherwise requested by NLC_SHAREDLOCK,
    * the last element of the namecache lookup will be locked
    * exclusively.
    *
    * NOTE: Even if we return on-zero, an unresolved namecache record
    *       will always be locked exclusively.
    */
   static __inline
   int
   wantsexcllock(struct nlookupdata *nd, const char *ptr)
   {
           if ((nd->nl_flags & NLC_SHAREDLOCK) == 0)
                   return(islastelement(ptr));
           return(0);
   }
   
   
   /*
    * Do a generic nlookup.  Note that the passed nd is not nlookup_done()'d
    * on return, even if an error occurs.  If no error occurs or NLC_CREATE
    * is flagged and ENOENT is returned, then the returned nl_nch is always
    * referenced and locked exclusively.
    *
    * WARNING: For any general error other than ENOENT w/NLC_CREATE, the
    *          the resulting nl_nch may or may not be locked and if locked
    *          might be locked either shared or exclusive.
    *
    * Intermediate directory elements, including the current directory, require
    * execute (search) permission.  nlookup does not examine the access 
    * permissions on the returned element.
    *
    * If NLC_CREATE is set the last directory must allow node creation,
    * and an error code of 0 will be returned for a non-existant
    * target (not ENOENT).
    *
    * If NLC_RENAME_DST is set the last directory mut allow node deletion,
    * plus the sticky check is made, and an error code of 0 will be returned
    * for a non-existant target (not ENOENT).
    *
    * If NLC_DELETE is set the last directory mut allow node deletion,
    * plus the sticky check is made.
    *
    * If NLC_REFDVP is set nd->nl_dvp will be set to the directory vnode
    * of the returned entry.  The vnode will be referenced, but not locked,
    * and will be released by nlookup_done() along with everything else.
    *
    * NOTE: As an optimization we attempt to obtain a shared namecache lock
    *       on any intermediate elements.  On success, the returned element
    *       is ALWAYS locked exclusively.
    */
   int
   nlookup(struct nlookupdata *nd)
   {
       globaldata_t gd = mycpu;
       struct nlcomponent nlc;
       struct nchandle nch;
       struct nchandle par;
       struct nchandle nctmp;
       struct mount *mp;
       struct vnode *hvp;          /* hold to prevent recyclement */
       int wasdotordotdot;
       char *ptr;
       int error;
       int len;
       int dflags;
       int hit = 1;
   
   #ifdef KTRACE
       if (KTRPOINT(nd->nl_td, KTR_NAMEI))
           ktrnamei(nd->nl_td->td_lwp, nd->nl_path);
   #endif
       bzero(&nlc, sizeof(nlc));
   
       /*
        * Setup for the loop.  The current working namecache element is
        * always at least referenced.  We lock it as required, but always
        * return a locked, resolved namecache entry.
        */
       nd->nl_loopcnt = 0;
       if (nd->nl_dvp) {
           vrele(nd->nl_dvp);
           nd->nl_dvp = NULL;
       }
       ptr = nd->nl_path;
   
       /*
        * Loop on the path components.  At the top of the loop nd->nl_nch
        * is ref'd and unlocked and represents our current position.
        */
       for (;;) {
           /*
            * Make sure nl_nch is locked so we can access the vnode, resolution
            * state, etc.
            */
           if ((nd->nl_flags & NLC_NCPISLOCKED) == 0) {
                   nd->nl_flags |= NLC_NCPISLOCKED;
                   cache_lock_maybe_shared(&nd->nl_nch, wantsexcllock(nd, ptr));
           }
   
           /*
            * Check if the root directory should replace the current
            * directory.  This is done at the start of a translation
            * or after a symbolic link has been found.  In other cases
            * ptr will never be pointing at a '/'.
            */
           if (*ptr == '/') {
               do {
                   ++ptr;
               } while (*ptr == '/');
               cache_unlock(&nd->nl_nch);
               cache_get_maybe_shared(&nd->nl_rootnch, &nch,
                                      wantsexcllock(nd, ptr));
               cache_drop(&nd->nl_nch);
               nd->nl_nch = nch;           /* remains locked */
   
               /*
                * Fast-track termination.  There is no parent directory of
                * the root in the same mount from the point of view of
                * the caller so return EACCES if NLC_REFDVP is specified,
                * and EEXIST if NLC_CREATE is also specified.
                * e.g. 'rmdir /' or 'mkdir /' are not allowed.
                */
               if (*ptr == 0) {
                   if (nd->nl_flags & NLC_REFDVP)
                           error = (nd->nl_flags & NLC_CREATE) ? EEXIST : EACCES;
                   else
                           error = 0;
                   break;
               }
               continue;
           }
   
           /*
            * Check directory search permissions (nd->nl_nch is locked & refd)
            */
           dflags = 0;
           error = naccess(&nd->nl_nch, NLC_EXEC, nd->nl_cred, &dflags);
           if (error)
               break;
   
           /*
            * Extract the path component.  Path components are limited to
            * 255 characters.
            */
           nlc.nlc_nameptr = ptr;
           while (*ptr && *ptr != '/')
               ++ptr;
           nlc.nlc_namelen = ptr - nlc.nlc_nameptr;
           if (nlc.nlc_namelen >= 256) {
               error = ENAMETOOLONG;
               break;
           }
   
           /*
            * Lookup the path component in the cache, creating an unresolved
            * entry if necessary.  We have to handle "." and ".." as special
            * cases.
            *
            * When handling ".." we have to detect a traversal back through a
            * mount point.   If we are at the root, ".." just returns the root.
            *
            * When handling "." or ".." we also have to recalculate dflags
            * since our dflags will be for some sub-directory instead of the
            * parent dir.
            *
            * This subsection returns a locked, refd 'nch' unless it errors out,
            * and an unlocked but still ref'd nd->nl_nch.
            *
            * The namecache topology is not allowed to be disconnected, so 
            * encountering a NULL parent will generate EINVAL.  This typically
            * occurs when a directory is removed out from under a process.
            *
            * WARNING! The unlocking of nd->nl_nch is sensitive code.
            */
           KKASSERT(nd->nl_flags & NLC_NCPISLOCKED);
   
           if (nlc.nlc_namelen == 1 && nlc.nlc_nameptr[0] == '.') {
               cache_unlock(&nd->nl_nch);
               nd->nl_flags &= ~NLC_NCPISLOCKED;
               cache_get_maybe_shared(&nd->nl_nch, &nch, wantsexcllock(nd, ptr));
               wasdotordotdot = 1;
           } else if (nlc.nlc_namelen == 2 && 
                      nlc.nlc_nameptr[0] == '.' && nlc.nlc_nameptr[1] == '.') {
               if (nd->nl_nch.mount == nd->nl_rootnch.mount &&
                   nd->nl_nch.ncp == nd->nl_rootnch.ncp
               ) {
                   /*
                    * ".." at the root returns the root
                    */
                   cache_unlock(&nd->nl_nch);
                   nd->nl_flags &= ~NLC_NCPISLOCKED;
                   cache_get_maybe_shared(&nd->nl_nch, &nch,
                                          wantsexcllock(nd, ptr));
               } else {
                   /*
                    * Locate the parent ncp.  If we are at the root of a
                    * filesystem mount we have to skip to the mounted-on
                    * point in the underlying filesystem.
                    *
                    * Expect the parent to always be good since the
                    * mountpoint doesn't go away.  XXX hack.  cache_get()
                    * requires the ncp to already have a ref as a safety.
                    */
                   nctmp = nd->nl_nch;
                   while (nctmp.ncp == nctmp.mount->mnt_ncmountpt.ncp)
                           nctmp = nctmp.mount->mnt_ncmounton;
                   nctmp.ncp = nctmp.ncp->nc_parent;
                   KKASSERT(nctmp.ncp != NULL);
                   cache_hold(&nctmp);
                   cache_unlock(&nd->nl_nch);
                   nd->nl_flags &= ~NLC_NCPISLOCKED;
                   cache_get_maybe_shared(&nctmp, &nch, wantsexcllock(nd, ptr));
                   cache_drop(&nctmp);             /* NOTE: zero's nctmp */
               }
               wasdotordotdot = 2;
           } else {
               /*
                * Must unlock nl_nch when traversing down the path.  However,
                * the child ncp has not yet been found/created and the parent's
                * child list might be empty.  Thus releasing the lock can
                * allow a race whereby the parent ncp's vnode is recycled.
                * This case can occur especially when maxvnodes is set very low.
                *
                * We need the parent's ncp to remain resolved for all normal
                * filesystem activities, so we vhold() the vp during the lookup
                * to prevent recyclement due to vnlru / maxvnodes.
                *
                * If we race an unlink or rename the ncp might be marked
                * DESTROYED after resolution, requiring a retry.
                */
               if ((hvp = nd->nl_nch.ncp->nc_vp) != NULL)
                   vhold(hvp);
               cache_unlock(&nd->nl_nch);
               nd->nl_flags &= ~NLC_NCPISLOCKED;
               error = cache_nlookup_maybe_shared(&nd->nl_nch, &nlc,
                                                  wantsexcllock(nd, ptr), &nch);
               if (error == EWOULDBLOCK) {
                       nch = cache_nlookup(&nd->nl_nch, &nlc);
                       if (nch.ncp->nc_flag & NCF_UNRESOLVED)
                           hit = 0;
                       for (;;) {
                           error = cache_resolve(&nch, nd->nl_cred);
                           if (error != EAGAIN &&
                               (nch.ncp->nc_flag & NCF_DESTROYED) == 0) {
                                   break;
                           }
                           kprintf("[diagnostic] nlookup: relookup %*.*s\n",
                                   nch.ncp->nc_nlen, nch.ncp->nc_nlen,
                                   nch.ncp->nc_name);
                           cache_put(&nch);
                           nch = cache_nlookup(&nd->nl_nch, &nlc);
                       }
               }
               if (hvp)
                   vdrop(hvp);
               wasdotordotdot = 0;
           }
   
           /*
            * If the last component was "." or ".." our dflags no longer
            * represents the parent directory and we have to explicitly
            * look it up.
            *
            * Expect the parent to be good since nch is locked.
            */
           if (wasdotordotdot && error == 0) {
               dflags = 0;
               if ((par.ncp = nch.ncp->nc_parent) != NULL) {
                   par.mount = nch.mount;
                   cache_hold(&par);
                   cache_lock_maybe_shared(&par, wantsexcllock(nd, ptr));
                   error = naccess(&par, 0, nd->nl_cred, &dflags);
                   cache_put(&par);
               }
           }
   
           /*
            * [end of subsection]
            *
            * nch is locked and referenced.
            * nd->nl_nch is unlocked and referenced.
            *
            * nl_nch must be unlocked or we could chain lock to the root
            * if a resolve gets stuck (e.g. in NFS).
            */
           KKASSERT((nd->nl_flags & NLC_NCPISLOCKED) == 0);
   
           /*
            * Resolve the namespace if necessary.  The ncp returned by
            * cache_nlookup() is referenced and locked.
            *
            * XXX neither '.' nor '..' should return EAGAIN since they were
            * previously resolved and thus cannot be newly created ncp's.
            */
           if (nch.ncp->nc_flag & NCF_UNRESOLVED) {
               hit = 0;
               error = cache_resolve(&nch, nd->nl_cred);
               KKASSERT(error != EAGAIN);
           } else {
               error = nch.ncp->nc_error;
           }
   
           /*
            * Early completion.  ENOENT is not an error if this is the last
            * component and NLC_CREATE or NLC_RENAME (rename target) was
            * requested.  Note that ncp->nc_error is left as ENOENT in that
            * case, which we check later on.
            *
            * Also handle invalid '.' or '..' components terminating a path
            * for a create/rename/delete.  The standard requires this and pax
            * pretty stupidly depends on it.
            */
           if (islastelement(ptr)) {
               if (error == ENOENT &&
                   (nd->nl_flags & (NLC_CREATE | NLC_RENAME_DST))
               ) {
                   if (nd->nl_flags & NLC_NFS_RDONLY) {
                           error = EROFS;
                   } else {
                           error = naccess(&nch, nd->nl_flags | dflags,
                                           nd->nl_cred, NULL);
                   }
               }
               if (error == 0 && wasdotordotdot &&
                   (nd->nl_flags & (NLC_CREATE | NLC_DELETE |
                                    NLC_RENAME_SRC | NLC_RENAME_DST))) {
                   /*
                    * POSIX junk
                    */
                   if (nd->nl_flags & NLC_CREATE)
                           error = EEXIST;
                   else if (nd->nl_flags & NLC_DELETE)
                           error = (wasdotordotdot == 1) ? EINVAL : ENOTEMPTY;
                   else
                           error = EINVAL;
               }
           }
   
           /*
            * Early completion on error.
            */
           if (error) {
               cache_put(&nch);
               break;
           }
   
           /*
            * If the element is a symlink and it is either not the last
            * element or it is the last element and we are allowed to
            * follow symlinks, resolve the symlink.
            */
           if ((nch.ncp->nc_flag & NCF_ISSYMLINK) &&
               (*ptr || (nd->nl_flags & NLC_FOLLOW))
           ) {
               if (nd->nl_loopcnt++ >= MAXSYMLINKS) {
                   error = ELOOP;
                   cache_put(&nch);
                   break;
               }
               error = nreadsymlink(nd, &nch, &nlc);
               cache_put(&nch);
               if (error)
                   break;
   
               /*
                * Concatenate trailing path elements onto the returned symlink.
                * Note that if the path component (ptr) is not exhausted, it
                * will being with a '/', so we do not have to add another one.
                *
                * The symlink may not be empty.
                */
               len = strlen(ptr);
               if (nlc.nlc_namelen == 0 || nlc.nlc_namelen + len >= MAXPATHLEN) {
                   error = nlc.nlc_namelen ? ENAMETOOLONG : ENOENT;
                   objcache_put(namei_oc, nlc.nlc_nameptr);
                   break;
               }
               bcopy(ptr, nlc.nlc_nameptr + nlc.nlc_namelen, len + 1);
               if (nd->nl_flags & NLC_HASBUF)
                   objcache_put(namei_oc, nd->nl_path);
               nd->nl_path = nlc.nlc_nameptr;
               nd->nl_flags |= NLC_HASBUF;
               ptr = nd->nl_path;
   
               /*
                * Go back up to the top to resolve any initial '/'s in the
                * symlink.
                */
               continue;
           }
   
           /*
            * If the element is a directory and we are crossing a mount point,
            * Locate the mount.
            */
           while ((nch.ncp->nc_flag & NCF_ISMOUNTPT) && 
               (nd->nl_flags & NLC_NOCROSSMOUNT) == 0 &&
               (mp = cache_findmount(&nch)) != NULL
           ) {
               struct vnode *tdp;
               int vfs_do_busy = 0;
   
               /*
                * VFS must be busied before the namecache entry is locked,
                * but we don't want to waste time calling vfs_busy() if the
                * mount point is already resolved.
                */
   again:
               cache_put(&nch);
               if (vfs_do_busy) {
                   while (vfs_busy(mp, 0)) {
                       if (mp->mnt_kern_flag & MNTK_UNMOUNT) {
                           kprintf("nlookup: warning umount race avoided\n");
                           cache_dropmount(mp);
                           error = EBUSY;
                           vfs_do_busy = 0;
                           goto double_break;
                       }
                   }
               }
               cache_get_maybe_shared(&mp->mnt_ncmountpt, &nch,
                                      wantsexcllock(nd, ptr));
   
               if (nch.ncp->nc_flag & NCF_UNRESOLVED) {
                   if (vfs_do_busy == 0) {
                       vfs_do_busy = 1;
                       goto again;
                   }
                   error = VFS_ROOT(mp, &tdp);
                   vfs_unbusy(mp);
                   vfs_do_busy = 0;
                   if (error) {
                       cache_dropmount(mp);
                       break;
                   }
                   cache_setvp(&nch, tdp);
                   vput(tdp);
               }
               if (vfs_do_busy)
                   vfs_unbusy(mp);
               cache_dropmount(mp);
           }
   
           if (error) {
               cache_put(&nch);
   double_break:
               break;
           }
               
           /*
            * Skip any slashes to get to the next element.  If there 
            * are any slashes at all the current element must be a
            * directory or, in the create case, intended to become a directory.
            * If it isn't we break without incrementing ptr and fall through
            * to the failure case below.
            */
           while (*ptr == '/') {
               if ((nch.ncp->nc_flag & NCF_ISDIR) == 0 && 
                   !(nd->nl_flags & NLC_WILLBEDIR)
               ) {
                   break;
               }
               ++ptr;
           }
   
           /*
            * Continuation case: additional elements and the current
            * element is a directory.
            */
           if (*ptr && (nch.ncp->nc_flag & NCF_ISDIR)) {
               cache_drop(&nd->nl_nch);
               cache_unlock(&nch);
               KKASSERT((nd->nl_flags & NLC_NCPISLOCKED) == 0);
               nd->nl_nch = nch;
               continue;
           }
   
           /*
            * Failure case: additional elements and the current element
            * is not a directory
            */
           if (*ptr) {
               cache_put(&nch);
               error = ENOTDIR;
               break;
           }
   
           /*
            * Successful lookup of last element.
            *
            * Check permissions if the target exists.  If the target does not
            * exist directory permissions were already tested in the early
            * completion code above.
            *
            * nd->nl_flags will be adjusted on return with NLC_APPENDONLY
            * if the file is marked append-only, and NLC_STICKY if the directory
            * containing the file is sticky.
            */
           if (nch.ncp->nc_vp && (nd->nl_flags & NLC_ALLCHKS)) {
               error = naccess(&nch, nd->nl_flags | dflags,
                               nd->nl_cred, NULL);
               if (error) {
                   cache_put(&nch);
                   break;
               }
           }
   
           /*
            * Termination: no more elements.
            *
            * If NLC_REFDVP is set acquire a referenced parent dvp.
            */
           if (nd->nl_flags & NLC_REFDVP) {
                   cache_lock(&nd->nl_nch);
                   error = cache_vref(&nd->nl_nch, nd->nl_cred, &nd->nl_dvp);
                   cache_unlock(&nd->nl_nch);
                   if (error) {
                           kprintf("NLC_REFDVP: Cannot ref dvp of %p\n", nch.ncp);
                           cache_put(&nch);
                           break;
                   }
           }
           cache_drop(&nd->nl_nch);
           nd->nl_nch = nch;
           nd->nl_flags |= NLC_NCPISLOCKED;
           error = 0;
           break;
       }
   
       if (hit)
           ++gd->gd_nchstats->ncs_longhits;
       else
           ++gd->gd_nchstats->ncs_longmiss;
   
       if (nd->nl_flags & NLC_NCPISLOCKED)
           KKASSERT(cache_lockstatus(&nd->nl_nch) > 0);
   
       /*
        * NOTE: If NLC_CREATE was set the ncp may represent a negative hit
        * (ncp->nc_error will be ENOENT), but we will still return an error
        * code of 0.
        */
       return(error);
   }
   
   /*
    * Resolve a mount point's glue ncp.  This ncp connects creates the illusion
    * of continuity in the namecache tree by connecting the ncp related to the
    * vnode under the mount to the ncp related to the mount's root vnode.
    *
    * If no error occured a locked, ref'd ncp is stored in *ncpp.
    */
   int
   nlookup_mp(struct mount *mp, struct nchandle *nch)
   {
       struct vnode *vp;
       int error;
   
       error = 0;
       cache_get(&mp->mnt_ncmountpt, nch);
       if (nch->ncp->nc_flag & NCF_UNRESOLVED) {
           while (vfs_busy(mp, 0))
               ;
           error = VFS_ROOT(mp, &vp);
           vfs_unbusy(mp);
           if (error) {
               cache_put(nch);
           } else {
               cache_setvp(nch, vp);
               vput(vp);
           }
       }
       return(error);
   }
   
   /*
    * Read the contents of a symlink, allocate a path buffer out of the
    * namei_oc and initialize the supplied nlcomponent with the result.
    *
    * If an error occurs no buffer will be allocated or returned in the nlc.
    */
   int
   nreadsymlink(struct nlookupdata *nd, struct nchandle *nch, 
                   struct nlcomponent *nlc)
   {
       struct vnode *vp;
       struct iovec aiov;
       struct uio auio;
       int linklen;
       int error;
       char *cp;
   
       nlc->nlc_nameptr = NULL;
       nlc->nlc_namelen = 0;
       if (nch->ncp->nc_vp == NULL)
           return(ENOENT);
       if ((error = cache_vget(nch, nd->nl_cred, LK_SHARED, &vp)) != 0)
           return(error);
       cp = objcache_get(namei_oc, M_WAITOK);
       aiov.iov_base = cp;
       aiov.iov_len = MAXPATHLEN;
       auio.uio_iov = &aiov;
       auio.uio_iovcnt = 1;
       auio.uio_offset = 0;
      auio.uio_rw = UIO_READ;
      auio.uio_segflg = UIO_SYSSPACE;
      auio.uio_td = nd->nl_td;
      auio.uio_resid = MAXPATHLEN - 1;
      error = VOP_READLINK(vp, &auio, nd->nl_cred);
      if (error)
          goto fail;
      linklen = MAXPATHLEN - 1 - auio.uio_resid;
      if (varsym_enable) {
          linklen = varsymreplace(cp, linklen, MAXPATHLEN - 1);
          if (linklen < 0) {
              error = ENAMETOOLONG;
              goto fail;
          }
      }
      cp[linklen] = 0;
      nlc->nlc_nameptr = cp;
      nlc->nlc_namelen = linklen;
      vput(vp);
      return(0);
  fail:
      objcache_put(namei_oc, cp);
      vput(vp);
      return(error);
  }
  
  /*
   * Check access [XXX cache vattr!] [XXX quota]
   *
   * Generally check the NLC_* access bits.   All specified bits must pass
   * for this function to return 0.
   *
   * The file does not have to exist when checking NLC_CREATE or NLC_RENAME_DST
   * access, otherwise it must exist.  No error is returned in this case.
   *
   * The file must not exist if NLC_EXCL is specified.
   *
   * Directory permissions in general are tested for NLC_CREATE if the file
   * does not exist, NLC_DELETE if the file does exist, and NLC_RENAME_DST
   * whether the file exists or not.
   *
   * The directory sticky bit is tested for NLC_DELETE and NLC_RENAME_DST,
   * the latter is only tested if the target exists.
   *
   * The passed ncp must be referenced and locked.  If it is already resolved
   * it may be locked shared but otherwise should be locked exclusively.
   */
  static int
  naccess(struct nchandle *nch, int nflags, struct ucred *cred, int *nflagsp)
  {
      struct vnode *vp;
      struct vattr va;
      struct namecache *ncp;
      int error;
      int cflags;
  
      KKASSERT(cache_lockstatus(nch) > 0);
  
      ncp = nch->ncp;
      if (ncp->nc_flag & NCF_UNRESOLVED) {
          cache_resolve(nch, cred);
          ncp = nch->ncp;
      }
      error = ncp->nc_error;
  
      /*
       * Directory permissions checks.  Silently ignore ENOENT if these
       * tests pass.  It isn't an error.
       *
       * We can safely resolve ncp->nc_parent because ncp is currently
       * locked.
       */
      if (nflags & (NLC_CREATE | NLC_DELETE | NLC_RENAME_SRC | NLC_RENAME_DST)) {
          if (((nflags & NLC_CREATE) && ncp->nc_vp == NULL) ||
              ((nflags & NLC_DELETE) && ncp->nc_vp != NULL) ||
              ((nflags & NLC_RENAME_SRC) && ncp->nc_vp != NULL) ||
              (nflags & NLC_RENAME_DST)
          ) {
              struct nchandle par;
  
              if ((par.ncp = ncp->nc_parent) == NULL) {
                  if (error != EAGAIN)
                          error = EINVAL;
              } else if (error == 0 || error == ENOENT) {
                  par.mount = nch->mount;
                  cache_hold(&par);
                  cache_lock_maybe_shared(&par, 0);
                  error = naccess(&par, NLC_WRITE, cred, NULL);
                  cache_put(&par);
              }
          }
      }
  
      /*
       * NLC_EXCL check.  Target file must not exist.
       */
      if (error == 0 && (nflags & NLC_EXCL) && ncp->nc_vp != NULL)
          error = EEXIST;
  
      /*
       * Get the vnode attributes so we can do the rest of our checks.
       *
       * NOTE: We only call naccess_va() if the target exists.
       */
      if (error == 0) {
          error = cache_vget(nch, cred, LK_SHARED, &vp);
          if (error == ENOENT) {
              /*
               * Silently zero-out ENOENT if creating or renaming
               * (rename target).  It isn't an error.
               */
              if (nflags & (NLC_CREATE | NLC_RENAME_DST))
                  error = 0;
          } else if (error == 0) {
              /*
               * Get the vnode attributes and check for illegal O_TRUNC
               * requests and read-only mounts.
               *
               * NOTE: You can still open devices on read-only mounts for
               *       writing.
               *
               * NOTE: creates/deletes/renames are handled by the NLC_WRITE
               *       check on the parent directory above.
               *
               * XXX cache the va in the namecache or in the vnode
               */
              error = VOP_GETATTR(vp, &va);
              if (error == 0 && (nflags & NLC_TRUNCATE)) {
                  switch(va.va_type) {
                  case VREG:
                  case VDATABASE:
                  case VCHR:
                  case VBLK:
                  case VFIFO:
                      break;
                  case VDIR:
                      error = EISDIR;
                      break;
                  default:
                      error = EINVAL;
                      break;
                  }
              }
              if (error == 0 && (nflags & NLC_WRITE) && vp->v_mount &&
                  (vp->v_mount->mnt_flag & MNT_RDONLY)
              ) {
                  switch(va.va_type) {
                  case VDIR:
                  case VLNK:
                  case VREG:
                  case VDATABASE:
                      error = EROFS;
                      break;
                  default:
                      break;
                  }
              }
              vput(vp);
  
              /*
               * Check permissions based on file attributes.  The passed
               * flags (*nflagsp) are modified with feedback based on
               * special attributes and requirements.
               */
              if (error == 0) {
                  /*
                   * Adjust the returned (*nflagsp) if non-NULL.
                   */
                  if (nflagsp) {
                      if ((va.va_mode & VSVTX) && va.va_uid != cred->cr_uid)
                          *nflagsp |= NLC_STICKY;
                      if (va.va_flags & APPEND)
                          *nflagsp |= NLC_APPENDONLY;
                      if (va.va_flags & IMMUTABLE)
                          *nflagsp |= NLC_IMMUTABLE;
                  }
  
                  /*
                   * Track swapcache management flags in the namecache.
                   *
                   * Calculate the flags based on the current vattr info
                   * and recalculate the inherited flags from the parent
                   * (the original cache linkage may have occurred without
                   * getattrs and thus have stale flags).
                   */
                  cflags = 0;
                  if (va.va_flags & SF_NOCACHE)
                          cflags |= NCF_SF_NOCACHE;
                  if (va.va_flags & UF_CACHE)
                          cflags |= NCF_UF_CACHE;
                  if (ncp->nc_parent) {
                          if (ncp->nc_parent->nc_flag &
                              (NCF_SF_NOCACHE | NCF_SF_PNOCACHE)) {
                                  cflags |= NCF_SF_PNOCACHE;
                          }
                          if (ncp->nc_parent->nc_flag &
                              (NCF_UF_CACHE | NCF_UF_PCACHE)) {
                                  cflags |= NCF_UF_PCACHE;
                          }
                  }
  
                  /*
                   * XXX we're not supposed to update nc_flag when holding
                   *     a shared lock.
                   */
                  atomic_clear_short(&ncp->nc_flag,
                                     (NCF_SF_NOCACHE | NCF_UF_CACHE |
                                     NCF_SF_PNOCACHE | NCF_UF_PCACHE) & ~cflags);
                  atomic_set_short(&ncp->nc_flag, cflags);
  
                  /*
                   * Process general access.
                   */
                  error = naccess_va(&va, nflags, cred);
              }
          }
      }
      return(error);
  }
  
  /*
   * Check the requested access against the given vattr using cred.
   */
  int
  naccess_va(struct vattr *va, int nflags, struct ucred *cred)
  {
      int i;
      int vmode;
  
      /*
       * Test the immutable bit.  Creations, deletions, renames (source
       * or destination) are not allowed.  chown/chmod/other is also not
       * allowed but is handled by SETATTR.  Hardlinks to the immutable
       * file are allowed.
       *
       * If the directory is set to immutable then creations, deletions,
       * renames (source or dest) and hardlinks to files within the directory
       * are not allowed, and regular files opened through the directory may
       * not be written to or truncated (unless a special device).
       *
       * NOTE!  New hardlinks to immutable files work but new hardlinks to
       * files, immutable or not, sitting inside an immutable directory are
       * not allowed.  As always if the file is hardlinked via some other
       * path additional hardlinks may be possible even if the file is marked
       * immutable.  The sysop needs to create a closure by checking the hard
       * link count.  Once closure is achieved you are good, and security
       * scripts should check link counts anyway.
       *
       * Writes and truncations are only allowed on special devices.
       */
      if ((va->va_flags & IMMUTABLE) || (nflags & NLC_IMMUTABLE)) {
          if ((nflags & NLC_IMMUTABLE) && (nflags & NLC_HLINK))
              return (EPERM);
          if (nflags & (NLC_CREATE | NLC_DELETE |
                        NLC_RENAME_SRC | NLC_RENAME_DST)) {
              return (EPERM);
          }
          if (nflags & (NLC_WRITE | NLC_TRUNCATE)) {
              switch(va->va_type) {
              case VDIR:
                  return (EISDIR);
              case VLNK:
              case VREG:
              case VDATABASE:
                  return (EPERM);
              default:
                  break;
              }
          }
      }
  
      /*
       * Test the no-unlink and append-only bits for opens, rename targets,
       * and deletions.  These bits are not tested for creations or
       * rename sources.
       *
       * Unlike FreeBSD we allow a file with APPEND set to be renamed.
       * If you do not wish this you must also set NOUNLINK.
       *
       * If the governing directory is marked APPEND-only it implies
       * NOUNLINK for all entries in the directory.
       */
      if (((va->va_flags & NOUNLINK) || (nflags & NLC_APPENDONLY)) &&
          (nflags & (NLC_DELETE | NLC_RENAME_SRC | NLC_RENAME_DST))
      ) {
          return (EPERM);
      }
  
      /*
       * A file marked append-only may not be deleted but can be renamed.
       */
      if ((va->va_flags & APPEND) &&
          (nflags & (NLC_DELETE | NLC_RENAME_DST))
      ) {
          return (EPERM);
      }
  
      /*
       * A file marked append-only which is opened for writing must also
       * be opened O_APPEND.
       */
      if ((va->va_flags & APPEND) && (nflags & (NLC_OPEN | NLC_TRUNCATE))) {
          if (nflags & NLC_TRUNCATE)
              return (EPERM);
          if ((nflags & (NLC_OPEN | NLC_WRITE)) == (NLC_OPEN | NLC_WRITE)) {
              if ((nflags & NLC_APPEND) == 0)
                  return (EPERM);
          }
      }
  
      /*
       * root gets universal access
       */
      if (cred->cr_uid == 0)
          return(0);
  
      /*
       * Check owner perms.
       *
       * If NLC_OWN is set the owner of the file is allowed no matter when
       * the owner-mode bits say (utimes).
       */
      vmode = 0;
      if (nflags & NLC_READ)
          vmode |= S_IRUSR;
      if (nflags & NLC_WRITE)
          vmode |= S_IWUSR;
      if (nflags & NLC_EXEC)
          vmode |= S_IXUSR;
  
      if (cred->cr_uid == va->va_uid) {
          if ((nflags & NLC_OWN) == 0) {
              if ((vmode & va->va_mode) != vmode)
                  return(EACCES);
          }
          return(0);
      }
  
      /*
       * If NLC_STICKY is set only the owner may delete or rename a file.
       * This bit is typically set on /tmp.
       *
       * Note that the NLC_READ/WRITE/EXEC bits are not typically set in
       * the specific delete or rename case.  For deletions and renames we
       * usually just care about directory permissions, not file permissions.
       */
      if ((nflags & NLC_STICKY) &&
          (nflags & (NLC_RENAME_SRC | NLC_RENAME_DST | NLC_DELETE))) {
          return(EACCES);
      }
  
      /*
       * Check group perms
       */
      vmode >>= 3;
      for (i = 0; i < cred->cr_ngroups; ++i) {
          if (va->va_gid == cred->cr_groups[i]) {
              if ((vmode & va->va_mode) != vmode)
                  return(EACCES);
              return(0);
          }
      }
  
      /*
       * Check world perms
       */
      vmode >>= 3;
      if ((vmode & va->va_mode) != vmode)
          return(EACCES);
      return(0);
  }
  

Cache object: 2a6b2039b2f34bad6b7334c327d2cd90