VGET(9)

NAME
vget - Acquire a primary reference, lock, and reactivate a vnode

SYNOPSIS
#include <sys/param.h>
#include <sys/vnode.h>
int
vget(struct vnode *vp, int lockflag);

DESCRIPTION
Acquire a primary reference to vnode and lock it, reactivating the vnode from the cache or free list if necessary. This kernel function must be used if the vnode in hand is not already known to be actively referenced, such as when obtaining the vnode pointer from a namecache or VM object structure.

vp  The vnode being acquired, typically obtained from some other system structure.

lockflag
    Must be LK_SHARED or LK_EXCLUSIVE. Passing 0 is illegal. LK_NOWAIT may be logically ORd in if you do not wish to block and can handle the additional error codes that might be returned.

When not in use, vnodes are kept on a free list or marked as being cached. The vnodes still reference valid files but may be reused to refer to a new file at any time. Often, references to these vnodes are present in auxiliary structures related to the vnode, such as namecache entries and VM objects.

When acquiring a vnode pointer from these auxiliary structures the vget function must be used to both reference and, if necessary, reactivate the vnode. The vnode will also be locked accordingly.

RETURN VALUES
0 is returned on success, ENOENT is returned if the vnode becomes unusable while vget is blocked trying to lock it, and other errors may be returned as well. ENOENT is not typically considered to be a fatal error but simply an indication that the caller needs to relookup the vnode as related structures may be in the midst of being destroyed.

SEE ALSO
vdrop(9), vhold(9), vnode(9), vn_lock(9), vn_unlock(9), vput(9), vref(9), vrele(9)

AUTHORS
This manual page was written by Doug Rabson.