vop_lock(9)

NAME

VOP_LOCK, VOP_UNLOCK, VOP_ISLOCKED, vn_lock - serialize ac

cess to a vnode

SYNOPSIS

#include <sys/param.h>
#include <sys/lock.h>
#include <sys/vnode.h>
int
VOP_LOCK(struct vnode *vp, int flags, struct thread *td);
int
VOP_UNLOCK(struct vnode *vp, int flags, struct thread *td);
int
VOP_ISLOCKED(struct vnode *vp, struct thread *td);
int
vn_lock(struct vnode *vp, int flags, struct thread *td);

DESCRIPTION

These calls are used to serialize access to the file system,

such as to
prevent two writes to the same file from happening at the

same time.

The arguments are:

vp The vnode being locked or unlocked.

flags One of the lock request types:

LK_SHARED Shared lock.
LK_EXCLUSIVE Exclusive lock.
LK_UPGRADE Shared-to-exclusive up

grade.
LK_EXCLUPGRADE First shared-to-exclusive

upgrade.
LK_DOWNGRADE Exclusive-to-shared down

grade.
LK_RELEASE Release any type of lock.
LK_DRAIN Wait for all lock activity

to end.

The lock type may be or'ed with these lock flags:

LK_NOWAIT Do not sleep to wait for

lock.
LK_SLEEPFAIL Sleep, then return failure.
LK_CANRECURSE Allow recursive exclusive

lock.
LK_REENABLE Lock is to be reenabled af

ter drain.
LK_NOPAUSE No spinloop.

The lock type may be or'ed with these control flags:

LK_INTERLOCK Specify when the caller al

ready has a

simple lock (VOP_LOCK()

will unlock the
simple lock after getting

the lock).

LK_RETRY Retry until locked.
LK_NOOBJ Do not create object.

td Thread context to use for the locks.

Kernel code should use vn_lock() to lock a vnode rather than

calling
VOP_LOCK() directly.

RETURN VALUES

Zero is returned on success, otherwise an error is returned.

PSEUDOCODE

struct vopnode {

int von_flag;
/*

* Other file system specific data.
*/

...;

};
#define VON_LOCKED 1
#define VON_WANTED 2
#define VTOVON(vp) ((struct vopnode *) (vp)->v_data)

int
vop_lock(struct vnode *vp)
{

struct vopnode* vop;

start:

while (vp->v_flag & VXLOCK) {

vp->v_flag |= VXWANT;
tsleep((caddr_t)vp, PINOD, "voplk1", 0);

}
if (vp->v_tag == VT_NON)

return ENOENT;

vop = VTOVON(vp);
if (vop->von_flag & VON_LOCKED) {

vop->von_flag |= VON_WANTED;
tsleep((caddr_t) vop, PINOD, "voplk2", 0);
goto start;

}

vop->von_flag |= VON_LOCKED;

return 0;

}

int
vop_unlock(struct vnode *vp)
{

struct vopnode *vop = VTOVON(vp);

if ((vop->von_flag & VON_LOCKED) == 0) {

panic("vop_unlock not locked");

}
vop->von_flag &= ~VON_LOCKED;
if (vop->von_flag & VON_WANTED) {

vop->von_flag &= ~VON_WANTED;
wakeup((caddr_t) vop);

}

return 0;

}

int
vop_islocked(struct vnode *vp)
{

struct vopnode *vop = VTOVON(vp);

if (vop->von_flag & VON_LOCKED)

return 1;

else

return 0;

}

SEE ALSO

vnode(9)

AUTHORS

This manual page was written by Doug Rabson.

BSD July 24, 1996

BSD