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VOP_LOCK.9freebsd

BSD mandoc

NAME

VOP_LOCK VOP_UNLOCK VOP_ISLOCKED vn_lock - serialize access to a vnode

SYNOPSIS

In sys/param.h In sys/lock.h In sys/vnode.h Ft int Fn VOP_LOCK struct vnode *vp int flags struct thread *td Ft int Fn VOP_UNLOCK struct vnode *vp int flags struct thread *td Ft int Fn VOP_ISLOCKED struct vnode *vp struct thread *td Ft int Fn 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:

Fa vp

The vnode being locked or unlocked.

Fa 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 Fn ( VOP_LOCK will unlock the simple lock after getting the lock).

LK_RETRY

Retry until locked.

LK_NOOBJ

Do not create object.

Fa td

Thread context to use for the locks.

Kernel code should use Fn vn_lock to lock a vnode rather than calling Fn 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 An Doug Rabson .