VOP_LOCK(9) MidnightBSD Kernel Developer’s Manual VOP_LOCK(9)

NAME

VOP_LOCK, VOP_UNLOCK, VOP_ISLOCKED, vn_lock — serialize access 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 upgrade.

LK_EXCLUPGRADE

First shared-to-exclusive upgrade.

LK_DOWNGRADE

Exclusive-to-shared downgrade.

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 after drain.

LK_NOPAUSE

No spinloop.

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

LK_INTERLOCK

Specify when the caller already 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.

MidnightBSD 0.3 July 24, 1996 MidnightBSD 0.3