VREF(9) BSD Kernel Developer's Manual VREF(9)NAMEvref — Increment the primary reference count for an active vnode
SYNOPSIS
#include <sys/param.h>
#include <sys/vnode.h>
void
vref(struct vnode *vp);
DESCRIPTION
The primary reference count for an active vnode is incremented. The
vnode must already have active references to it, usually acquired prior
to the vnode pointer being passed to the code making this call or when
vnode pointers are obtained from structures, such as file pointers, which
hold an active reference to the vnode. Any attempt to use vref on an
inactive vnode will result in a panic.
vp The vnode being referenced.
Each vnode maintains a Primary and Auxiliary reference count. The pri‐
mary reference count prevents the vnode from being deactivated while the
auxiliary reference count keeps track of auxiliary structures, such as
namecache and VM object structures, which are typically kept associated
with the vnode for caching purposes even after the vnode has been deacti‐
vated.
A procedure will often acquire its own primary reference to a vnode to
prevent the vnode from getting ripped out from under it during an opera‐
tion due to the destruction of the parent data structure. For example,
one thread may be blocked on a vnode operation related to a file descrip‐
tor that another thread then closes.
SEE ALSOvdrop(9), vget(9), vhold(9), vnode(9), vn_lock(9), vn_unlock(9), vput(9),
vrele(9)AUTHORS
This manual page was written by Doug Rabson.
BSD May 5, 2007 BSD
