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 January 10, 2008 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.In sys/param.h 42.In sys/lock.h 43.In sys/vnode.h 44.Ft int 45.Fn VOP_LOCK "struct vnode *vp" "int flags" "struct thread *td" 46.Ft int 47.Fn VOP_UNLOCK "struct vnode *vp" "int flags" "struct thread *td" 48.Ft int 49.Fn VOP_ISLOCKED "struct vnode *vp" "struct thread *td" 50.Ft int 51.Fn vn_lock "struct vnode *vp" "int flags" 52.Sh DESCRIPTION 53These calls are used to serialize access to the file system, 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 Fa vp 60The vnode being locked or unlocked. 61.It Fa flags 62One of the lock request types: 63.Pp 64.Bl -tag -width ".Dv LK_CANRECURSE" -offset indent -compact 65.It Dv LK_SHARED 66Shared lock. 67.It Dv LK_EXCLUSIVE 68Exclusive lock. 69.It Dv LK_UPGRADE 70Shared-to-exclusive upgrade. 71.It Dv LK_DOWNGRADE 72Exclusive-to-shared downgrade. 73.It Dv LK_RELEASE 74Release any type of lock. 75.It Dv LK_DRAIN 76Wait for all lock activity to end. 77.El 78.Pp 79The lock type may be 80.Em or Ns 'ed 81with these lock flags: 82.Pp 83.Bl -tag -width ".Dv LK_CANRECURSE" -offset indent -compact 84.It Dv LK_NOWAIT 85Do not sleep to wait for lock. 86.It Dv LK_SLEEPFAIL 87Sleep, then return failure. 88.It Dv LK_CANRECURSE 89Allow recursive exclusive lock. 90.El 91.Pp 92The lock type may be 93.Em or Ns 'ed 94with these control flags: 95.Pp 96.Bl -tag -width ".Dv LK_CANRECURSE" -offset indent -compact 97.It Dv LK_INTERLOCK 98Specify when the caller already has a simple lock 99.Fn ( VOP_LOCK 100will unlock the simple lock after getting the lock). 101.It Dv LK_RETRY 102Retry until locked. 103.El 104.It Fa td 105Thread context to use for the locks. 106.El 107.Pp 108Kernel code should use 109.Fn vn_lock 110to lock a vnode rather than calling 111.Fn VOP_LOCK 112directly. 113.Fn vn_lock 114also does not want a thread specified as argument but it 115assumes curthread to be used. 116.Sh RETURN VALUES 117Zero is returned on success, otherwise an error is returned. 118.Sh PSEUDOCODE 119.Bd -literal 120struct vopnode { 121 int von_flag; 122 /* 123 * Other file system specific data. 124 */ 125 ...; 126}; 127#define VON_LOCKED 1 128#define VON_WANTED 2 129#define VTOVON(vp) ((struct vopnode *) (vp)->v_data) 130 131int 132vop_lock(struct vnode *vp) 133{ 134 struct vopnode* vop; 135 136start: 137 while (vp->v_flag & VXLOCK) { 138 vp->v_flag |= VXWANT; 139 tsleep((caddr_t)vp, PINOD, "voplk1", 0); 140 } 141 if (vp->v_tag == VT_NON) 142 return ENOENT; 143 144 vop = VTOVON(vp); 145 if (vop->von_flag & VON_LOCKED) { 146 vop->von_flag |= VON_WANTED; 147 tsleep((caddr_t) vop, PINOD, "voplk2", 0); 148 goto start; 149 } 150 151 vop->von_flag |= VON_LOCKED; 152 153 return 0; 154} 155 156int 157vop_unlock(struct vnode *vp) 158{ 159 struct vopnode *vop = VTOVON(vp); 160 161 if ((vop->von_flag & VON_LOCKED) == 0) { 162 panic("vop_unlock not locked"); 163 } 164 vop->von_flag &= ~VON_LOCKED; 165 if (vop->von_flag & VON_WANTED) { 166 vop->von_flag &= ~VON_WANTED; 167 wakeup((caddr_t) vop); 168 } 169 170 return 0; 171} 172 173int 174vop_islocked(struct vnode *vp) 175{ 176 struct vopnode *vop = VTOVON(vp); 177 178 if (vop->von_flag & VON_LOCKED) 179 return 1; 180 else 181 return 0; 182} 183.Ed 184.Sh SEE ALSO 185.Xr vnode 9 186.Sh AUTHORS 187This manual page was written by 188.An Doug Rabson . 189