1.\" -*- nroff -*- 2.\" 3.\" Copyright (c) 1996 Doug Rabson 4.\" 5.\" All rights reserved. 6.\" 7.\" This program is free software. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 19.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 20.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 21.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 22.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 23.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 27.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28.\" 29.\" $Id: VOP_LOCK.9,v 1.5 1999/03/17 20:17:32 ghelmer Exp $ 30.\" 31.Dd July 24, 1996 32.Os 33.Dt VOP_LOCK 9 34.Sh NAME 35.Nm VOP_LOCK , 36.Nm VOP_UNLOCK , 37.Nm VOP_ISLOCKED , 38.Nm vn_lock 39.Nd serialize access to a vnode 40.Sh SYNOPSIS 41.Fd #include <sys/param.h> 42.Fd #include <sys/lock.h> 43.Fd #include <sys/vnode.h> 44.Ft int 45.Fn VOP_LOCK "struct vnode *vp" "int flags" "struct proc *p" 46.Ft int 47.Fn VOP_UNLOCK "struct vnode *vp" "int flags" "struct proc *p" 48.Ft int 49.Fn VOP_ISLOCKED "struct vnode *vp" 50.Ft int 51.Fn vn_lock "struct vnode *vp" "int flags" "struct proc *p" 52.Sh DESCRIPTION 53.Pp 54These calls are used to serialize access to the filesystem, such as 55to prevent two writes to the same file from happening at the 56same time. 57.Pp 58The arguments are: 59.Bl -tag -width flags 60.It Ar vp 61the vnode being locked or unlocked 62.It Ar flags 63One of the lock request types: 64.Bl -column LK_EXCLUPGRADE -offset indent 65.It Dv LK_SHARED Ta "Shared lock" 66.It Dv LK_EXCLUSIVE Ta "Exclusive lock" 67.It Dv LK_UPGRADE Ta "Shared-to-exclusive upgrade" 68.It Dv LK_EXCLUPGRADE Ta "First shared-to-exclusive upgrade" 69.It Dv LK_DOWNGRADE Ta "Exclusive-to-shared downgrade" 70.It Dv LK_RELEASE Ta "Release any type of lock" 71.It Dv LK_DRAIN Ta "Wait for all lock activity to end" 72.El 73.Pp 74The lock type may be 75.Em or Ns 'ed 76with these lock flags: 77.Bl -column LK_CANRECURSE -offset indent 78.It Dv LK_NOWAIT Ta "Do not sleep to wait for lock" 79.It Dv LK_SLEEPFAIL Ta "Sleep, then return failure" 80.It Dv LK_CANRECURSE Ta "Allow recursive exclusive lock" 81.It Dv LK_REENABLE Ta "Lock is to be reenabled after drain" 82.It Dv LK_NOPAUSE Ta "No spinloop" 83.El 84.Pp 85The lock type may be 86.Em or Ns 'ed 87with these control flags: 88.Bl -column LK_INTERLOCK -offset indent 89.It Dv LK_INTERLOCK Ta "Specify when the caller already has a simple lock \ 90(VOP_LOCK will unlock the simple lock after getting the lock)" 91.It Dv LK_RETRY Ta "Retry until locked" 92.It Dv LK_NOOBJ Ta "Don't create object" 93.El 94.It Ar p 95process context to use for the locks 96.El 97.Pp 98Kernel code should use 99.Fn vn_lock 100to lock a vnode rather than calling 101.Fn VOP_LOCK 102directly. 103.Sh RETURN VALUES 104Zero is returned on success, otherwise an error is returned. 105.Sh PSEUDOCODE 106.Bd -literal 107struct vopnode { 108 int von_flag; 109 /* 110 * Other filesystem specific data. 111 */ 112 ...; 113}; 114#define VON_LOCKED 1 115#define VON_WANTED 2 116#define VTOVON(vp) ((struct vopnode *) (vp)->v_data) 117 118int 119vop_lock(struct vnode *vp) 120{ 121 struct vopnode* vop; 122 123start: 124 while (vp->v_flag & VXLOCK) { 125 vp->v_flag |= VXWANT; 126 tsleep((caddr_t)vp, PINOD, "voplk1", 0); 127 } 128 if (vp->v_tag == VT_NON) 129 return ENOENT; 130 131 vop = VTOVON(vp); 132 if (vop->von_flag & VON_LOCKED) { 133 vop->von_flag |= VON_WANTED; 134 tsleep((caddr_t) vop, PINOD, "voplk2", 0); 135 goto start; 136 } 137 138 vop->von_flag |= VON_LOCKED; 139 140 return 0; 141} 142 143int 144vop_unlock(struct vnode *vp) 145{ 146 struct vopnode *vop = VTOVON(vp); 147 148 if ((vop->von_flag & VON_LOCKED) == 0) { 149 panic("vop_unlock not locked"); 150 } 151 vop->von_flag &= ~VON_LOCKED; 152 if (vop->von_flag & VON_WANTED) { 153 vop->von_flag &= ~VON_WANTED; 154 wakeup((caddr_t) vop); 155 } 156 157 return 0; 158} 159 160int 161vop_islocked(struct vnode *vp) 162{ 163 struct vopnode *vop = VTOVON(vp); 164 165 if (vop->von_flag & VON_LOCKED) 166 return 1; 167 else 168 return 0; 169} 170.Ed 171.Sh SEE ALSO 172.Xr vnode 9 173.Sh AUTHORS 174This man page was written by 175.An Doug Rabson . 176