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.

       Cnp 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 */
               /*
                * 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 */
               u_long  cn_hash;        /* hash value of looked up name */
               long    cn_consume;     /* chars to consume in lookup() */
       };

       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.  If an error (note: the return  value  EJUSTRETURN  is  not
       considered an error) is detected, it will be returned locked.  Otherwise, it will be unlocked unless both
       LOCKPARENT  and  ISLASTCN are specified in cnp->cn_flags.  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.

Debian                                          November 24, 1997                                  VOP_LOOKUP(9)