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VOP_LOCK (9) | Kernel routines | Unix Manual Pages | :man

NAME

VOP_LOCK, VOP_UNLOCK, VOP_ISLOCKED, vn_lock - serialize access to a vnode

CONTENTS

Synopsis
Description
Return Values
Pseudocode
See Also
Authors

SYNOPSIS


.In sys/param.h
.In sys/lock.h
.In 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


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