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.\" $FreeBSD$ 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" "struct proc *p" 50.Ft int 51.Fn vn_lock "struct vnode *vp" "int flags" "struct proc *p" 52.Sh DESCRIPTION 53These calls are used to serialize access to the filesystem, such as 54to prevent two writes to the same file from happening at the 55same time. 56.Pp 57The arguments are: 58.Bl -tag -width flags 59.It Ar vp 60the vnode being locked or unlocked 61.It Ar flags 62One of the lock request types: 63.Bl -column LK_EXCLUPGRADE -offset indent 64.It Dv LK_SHARED Ta "Shared lock" 65.It Dv LK_EXCLUSIVE Ta "Exclusive lock" 66.It Dv LK_UPGRADE Ta "Shared-to-exclusive upgrade" 67.It Dv LK_EXCLUPGRADE Ta "First shared-to-exclusive upgrade" 68.It Dv LK_DOWNGRADE Ta "Exclusive-to-shared downgrade" 69.It Dv LK_RELEASE Ta "Release any type of lock" 70.It Dv LK_DRAIN Ta "Wait for all lock activity to end" 71.El 72.Pp 73The lock type may be 74.Em or Ns 'ed 75with these lock flags: 76.Bl -column LK_CANRECURSE -offset indent 77.It Dv LK_NOWAIT Ta "Do not sleep to wait for lock" 78.It Dv LK_SLEEPFAIL Ta "Sleep, then return failure" 79.It Dv LK_CANRECURSE Ta "Allow recursive exclusive lock" 80.It Dv LK_REENABLE Ta "Lock is to be reenabled after drain" 81.It Dv LK_NOPAUSE Ta "No spinloop" 82.El 83.Pp 84The lock type may be 85.Em or Ns 'ed 86with these control flags: 87.Bl -column LK_INTERLOCK -offset indent 88.It Dv LK_INTERLOCK Ta "Specify when the caller already has a simple lock \ 89(VOP_LOCK will unlock the simple lock after getting the lock)" 90.It Dv LK_RETRY Ta "Retry until locked" 91.It Dv LK_NOOBJ Ta "Don't create object" 92.El 93.It Ar p 94process context to use for the locks 95.El 96.Pp 97Kernel code should use 98.Fn vn_lock 99to lock a vnode rather than calling 100.Fn VOP_LOCK 101directly. 102.Sh RETURN VALUES 103Zero is returned on success, otherwise an error is returned. 104.Sh PSEUDOCODE 105.Bd -literal 106struct vopnode { 107 int von_flag; 108 /* 109 * Other filesystem specific data. 110 */ 111 ...; 112}; 113#define VON_LOCKED 1 114#define VON_WANTED 2 115#define VTOVON(vp) ((struct vopnode *) (vp)->v_data) 116 117int 118vop_lock(struct vnode *vp) 119{ 120 struct vopnode* vop; 121 122start: 123 while (vp->v_flag & VXLOCK) { 124 vp->v_flag |= VXWANT; 125 tsleep((caddr_t)vp, PINOD, "voplk1", 0); 126 } 127 if (vp->v_tag == VT_NON) 128 return ENOENT; 129 130 vop = VTOVON(vp); 131 if (vop->von_flag & VON_LOCKED) { 132 vop->von_flag |= VON_WANTED; 133 tsleep((caddr_t) vop, PINOD, "voplk2", 0); 134 goto start; 135 } 136 137 vop->von_flag |= VON_LOCKED; 138 139 return 0; 140} 141 142int 143vop_unlock(struct vnode *vp) 144{ 145 struct vopnode *vop = VTOVON(vp); 146 147 if ((vop->von_flag & VON_LOCKED) == 0) { 148 panic("vop_unlock not locked"); 149 } 150 vop->von_flag &= ~VON_LOCKED; 151 if (vop->von_flag & VON_WANTED) { 152 vop->von_flag &= ~VON_WANTED; 153 wakeup((caddr_t) vop); 154 } 155 156 return 0; 157} 158 159int 160vop_islocked(struct vnode *vp) 161{ 162 struct vopnode *vop = VTOVON(vp); 163 164 if (vop->von_flag & VON_LOCKED) 165 return 1; 166 else 167 return 0; 168} 169.Ed 170.Sh SEE ALSO 171.Xr vnode 9 172.Sh AUTHORS 173This man page was written by 174.An Doug Rabson . 175