VOP_LOOKUP(9)          FreeBSD Kernel Developer's Manual         VOP_LOOKUP(9)

NAME
     VOP_LOOKUP - lookup a component of a pathname

SYNOPSIS
     #include <sys/param.h>
     #include <sys/vnode.h>
     #include <sys/namei.h>

     int
     VOP_LOOKUP(struct vnode *dvp, struct vnode **vpp,
         struct componentname *cnp);

DESCRIPTION
     This entry point looks up a single pathname component in a given
     directory.

     Its arguments are:

     dvp  The locked vnode of the directory to search.

     vpp  The address of a variable where the resulting locked vnode should be
          stored.

     cnp  The pathname component to be searched for.  It is a pointer to a
          componentname structure defined as follows:

          struct componentname {
                  /*
                   * Arguments to lookup.
                   */
                  u_long  cn_nameiop;     /* namei operation */
                  u_long  cn_flags;       /* flags to namei */
                  struct  thread *cn_thread;      /* thread requesting lookup */
                  struct  ucred *cn_cred; /* credentials */
                  int     cn_lkflags;     /* Lock flags LK_EXCLUSIVE or LK_SHARED */
                  /*
                   * Shared between lookup and commit routines.
                   */
                  char    *cn_pnbuf;      /* pathname buffer */
                  char    *cn_nameptr;    /* pointer to looked up name */
                  long    cn_namelen;     /* length of looked up component */
          };

          Convert a component of a pathname into a pointer to a locked vnode.
          This is a very central and rather complicated routine.  If the file
          system is not maintained in a strict tree hierarchy, this can result
          in a deadlock situation.

          The cnp->cn_nameiop argument is LOOKUP, CREATE, RENAME, or DELETE
          depending on the intended use of the object.  When CREATE, RENAME,
          or DELETE is specified, information usable in creating, renaming, or
          deleting a directory entry may be calculated.

          Overall outline of VOP_LOOKUP:

                Check accessibility of directory.  Look for name in cache, if
                found, then return name.  Search for name in directory, goto
                to found or notfound as appropriate.

          notfound:

                If creating or renaming and at end of pathname, return
                EJUSTRETURN, leaving info on available slots else return
                ENOENT.

          found:

                If at end of path and deleting, return information to allow
                delete.  If at end of path and renaming, lock target inode and
                return info to allow rename.  If not at end, add name to
                cache; if at end and neither creating nor deleting, add name
                to cache.

LOCKS
     The directory dvp should be locked on entry and exit, regardless of error
     condition.  If an entry is found in the directory, it will be returned
     locked.

RETURN VALUES
     Zero is returned with *vpp set to the locked vnode of the file if the
     component is found.  If the component being searched for is ".", then the
     vnode just has an extra reference added to it with vref(9).  The caller
     must take care to release the locks appropriately in this case.

     If the component is not found and the operation is CREATE or RENAME, the
     flag ISLASTCN is specified and the operation would succeed, the special
     return value EJUSTRETURN is returned.  Otherwise, an appropriate error
     code is returned.

ERRORS
     [ENOTDIR]          The vnode dvp does not represent a directory.

     [ENOENT]           The component dvp was not found in this directory.

     [EACCES]           Access for the specified operation is denied.

     [EJUSTRETURN]      A CREATE or RENAME operation would be successful.

SEE ALSO
     vnode(9), VOP_ACCESS(9), VOP_CREATE(9), VOP_MKDIR(9), VOP_MKNOD(9),
     VOP_RENAME(9), VOP_SYMLINK(9)

HISTORY
     The function VOP_LOOKUP appeared in 4.3BSD.

AUTHORS
     This manual page was written by Doug Rabson, with some text from comments
     in ufs_lookup.c.

FreeBSD 13.1-RELEASE-p6         August 8, 2018         FreeBSD 13.1-RELEASE-p6