Copyright (c) 1996 Doug Rabson
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$FreeBSD: head/share/man/man9/VOP_LOCK.9 176562 2008-02-25 19:12:01Z attilio $
.Dd February 25, 2008 .Os .Dt VOP_LOCK 9 .Sh NAME .Nm VOP_LOCK , .Nm VOP_UNLOCK , .Nm VOP_ISLOCKED , .Nm vn_lock .Nd serialize access to a vnode .Sh SYNOPSIS n sys/param.h n sys/lock.h n sys/vnode.h .Ft int .Fn VOP_LOCK "struct vnode *vp" "int flags" .Ft int .Fn VOP_UNLOCK "struct vnode *vp" "int flags" .Ft int .Fn VOP_ISLOCKED "struct vnode *vp" .Ft int .Fn vn_lock "struct vnode *vp" "int flags" .Sh 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.
p The arguments are: l -tag -width flags t Fa vp The vnode being locked or unlocked. t Fa flags One of the lock request types:
p l -tag -width ".Dv LK_CANRECURSE" -offset indent -compact t Dv LK_SHARED Shared lock. t Dv LK_EXCLUSIVE Exclusive lock. t Dv LK_UPGRADE Shared-to-exclusive upgrade. t Dv LK_DOWNGRADE Exclusive-to-shared downgrade. t Dv LK_RELEASE Release any type of lock. t Dv LK_DRAIN Wait for all lock activity to end. .El
p The lock type may be .Em or Ns 'ed with these lock flags:
p l -tag -width ".Dv LK_CANRECURSE" -offset indent -compact t Dv LK_NOWAIT Do not sleep to wait for lock. t Dv LK_SLEEPFAIL Sleep, then return failure. t Dv LK_CANRECURSE Allow recursive exclusive lock. .El
p The lock type may be .Em or Ns 'ed with these control flags:
p l -tag -width ".Dv LK_CANRECURSE" -offset indent -compact t Dv LK_INTERLOCK Specify when the caller already has a simple lock .Fn ( VOP_LOCK will unlock the simple lock after getting the lock). t Dv LK_RETRY Retry until locked. .El
p Kernel code should use .Fn vn_lock to lock a vnode rather than calling .Fn VOP_LOCK directly. .Fn vn_lock also does not want a thread specified as argument but it assumes curthread to be used. .Sh RETURN VALUES Zero is returned on success, otherwise an error is returned. .Sh PSEUDOCODE d -literal 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; } .Ed .Sh SEE ALSO .Xr vnode 9 .Sh AUTHORS This manual page was written by .An Doug Rabson .