194 lines
4.6 KiB
Groff
194 lines
4.6 KiB
Groff
.\" -*- nroff -*-
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.\"
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.\" Copyright (c) 1996 Doug Rabson
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.\"
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.\" All rights reserved.
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.\"
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.\" This program is free software.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 24, 1996
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.Os
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.Dt VOP_LOCK 9
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.Sh NAME
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.Nm VOP_LOCK ,
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.Nm VOP_UNLOCK ,
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.Nm VOP_ISLOCKED ,
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.Nm vn_lock
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.Nd serialize access to a vnode
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/lock.h
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.In sys/vnode.h
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.Ft int
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.Fn VOP_LOCK "struct vnode *vp" "int flags" "struct thread *td"
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.Ft int
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.Fn VOP_UNLOCK "struct vnode *vp" "int flags" "struct thread *td"
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.Ft int
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.Fn VOP_ISLOCKED "struct vnode *vp" "struct thread *td"
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.Ft int
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.Fn vn_lock "struct vnode *vp" "int flags" "struct thread *td"
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.Sh DESCRIPTION
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These calls are used to serialize access to the file system, such as
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to prevent two writes to the same file from happening at the
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same time.
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.Pp
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The arguments are:
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.Bl -tag -width flags
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.It Fa vp
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The vnode being locked or unlocked.
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.It Fa flags
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One of the lock request types:
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.Pp
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.Bl -tag -width ".Dv LK_EXCLUPGRADE" -offset indent -compact
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.It Dv LK_SHARED
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Shared lock.
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.It Dv LK_EXCLUSIVE
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Exclusive lock.
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.It Dv LK_UPGRADE
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Shared-to-exclusive upgrade.
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.It Dv LK_EXCLUPGRADE
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First shared-to-exclusive upgrade.
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.It Dv LK_DOWNGRADE
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Exclusive-to-shared downgrade.
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.It Dv LK_RELEASE
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Release any type of lock.
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.It Dv LK_DRAIN
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Wait for all lock activity to end.
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.El
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.Pp
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The lock type may be
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.Em or Ns 'ed
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with these lock flags:
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.Pp
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.Bl -tag -width ".Dv LK_EXCLUPGRADE" -offset indent -compact
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.It Dv LK_NOWAIT
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Do not sleep to wait for lock.
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.It Dv LK_SLEEPFAIL
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Sleep, then return failure.
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.It Dv LK_CANRECURSE
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Allow recursive exclusive lock.
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.It Dv LK_REENABLE
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Lock is to be reenabled after drain.
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.It Dv LK_NOPAUSE
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No spinloop.
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.El
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.Pp
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The lock type may be
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.Em or Ns 'ed
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with these control flags:
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.Pp
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.Bl -tag -width ".Dv LK_EXCLUPGRADE" -offset indent -compact
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.It Dv LK_INTERLOCK
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Specify when the caller already has a simple lock
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.Fn ( VOP_LOCK
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will unlock the simple lock after getting the lock).
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.It Dv LK_RETRY
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Retry until locked.
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.It Dv LK_NOOBJ
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Do not create object.
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.El
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.It Fa td
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Thread context to use for the locks.
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.El
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.Pp
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Kernel code should use
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.Fn vn_lock
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to lock a vnode rather than calling
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.Fn VOP_LOCK
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directly.
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.Sh RETURN VALUES
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Zero is returned on success, otherwise an error is returned.
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.Sh PSEUDOCODE
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.Bd -literal
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struct vopnode {
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int von_flag;
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/*
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* Other file system specific data.
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*/
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...;
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};
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#define VON_LOCKED 1
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#define VON_WANTED 2
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#define VTOVON(vp) ((struct vopnode *) (vp)->v_data)
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int
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vop_lock(struct vnode *vp)
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{
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struct vopnode* vop;
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start:
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while (vp->v_flag & VXLOCK) {
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vp->v_flag |= VXWANT;
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tsleep((caddr_t)vp, PINOD, "voplk1", 0);
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}
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if (vp->v_tag == VT_NON)
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return ENOENT;
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vop = VTOVON(vp);
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if (vop->von_flag & VON_LOCKED) {
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vop->von_flag |= VON_WANTED;
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tsleep((caddr_t) vop, PINOD, "voplk2", 0);
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goto start;
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}
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vop->von_flag |= VON_LOCKED;
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return 0;
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}
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int
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vop_unlock(struct vnode *vp)
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{
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struct vopnode *vop = VTOVON(vp);
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if ((vop->von_flag & VON_LOCKED) == 0) {
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panic("vop_unlock not locked");
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}
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vop->von_flag &= ~VON_LOCKED;
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if (vop->von_flag & VON_WANTED) {
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vop->von_flag &= ~VON_WANTED;
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wakeup((caddr_t) vop);
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}
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return 0;
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}
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int
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vop_islocked(struct vnode *vp)
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{
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struct vopnode *vop = VTOVON(vp);
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if (vop->von_flag & VON_LOCKED)
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return 1;
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else
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return 0;
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}
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.Ed
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.Sh SEE ALSO
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.Xr vnode 9
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.Sh AUTHORS
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This man page was written by
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.An Doug Rabson .
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