DragonFly On-Line Manual Pages

VREF(9)               DragonFly Kernel Developer's Manual              VREF(9)

NAME
     vref -- 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 ALSO
     vdrop(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.

DragonFly 3.5                     May 5, 2007                    DragonFly 3.5