1.\" 2.\" Copyright (C) 2002 Chad David <davidc@acns.ab.ca>. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice(s), this list of conditions and the following disclaimer as 9.\" the first lines of this file unmodified other than the possible 10.\" addition of one or more copyright notices. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice(s), this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 16.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 17.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 18.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY 19.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 20.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 21.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 22.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 25.\" DAMAGE. 26.\" 27.\" $FreeBSD: src/share/man/man9/lock.9,v 1.11 2003/09/08 19:57:21 ru Exp $ 28.\" $DragonFly: src/share/man/man9/lock.9,v 1.5 2006/06/29 19:56:19 swildner Exp $ 29.\" 30.Dd June 29, 2006 31.Dt LOCK 9 32.Os 33.Sh NAME 34.Nm lockinit , 35.Nm lockcount , 36.Nm lockmgr , 37.Nm lockstatus , 38.Nm lockmgr_printinfo 39.Nd "lockmgr family of functions" 40.Sh SYNOPSIS 41.In sys/types.h 42.In sys/lock.h 43.Ft void 44.Fn lockinit "struct lock *lkp" "char *wmesg" "int timo" "int flags" 45.Ft int 46.Fn lockcount "struct lock *lkp" 47.Ft int 48.Fn lockcountnb "struct lock *lkp" 49.Ft int 50.Fn lockmgr "struct lock *lkp" "u_int flags" 51.Ft int 52.Fn lockstatus "struct lock *lkp" "struct thread *td" 53.Ft void 54.Fn lockmgr_printinfo "struct lock *lkp" 55.Sh DESCRIPTION 56The 57.Fn lockinit 58function is used to initialize a lock. 59It must be called before any operation can be performed on a lock. 60Its arguments are: 61.Bl -tag -width ".Fa wmesg" 62.It Fa lkp 63A pointer to the lock to initialize. 64.It Fa wmesg 65The lock message. 66This is used for both debugging output and 67.Xr tsleep 9 . 68.It Fa timo 69The timeout value passed to 70.Xr tsleep 9 . 71.It Fa flags 72The flags the lock is to be initialized with. 73.Bl -tag -width ".Dv LG_CANRECURSE" 74.It Dv LK_NOWAIT 75Do not sleep while acquiring the lock. 76.It Dv LK_SLEEPFAIL 77Fail after a sleep. 78.It Dv LK_CANRECURSE 79Allow recursive exclusive locks. 80.It Dv LK_NOPAUSE 81Disable the spinlock while acquiring the lock. 82.It Dv LK_TIMELOCK 83Use 84.Fa timo 85during a sleep; otherwise, 0 is used. 86.El 87.El 88.Pp 89The 90.Fn lockcount 91function returns a count of the number of exclusive locks and shared locks 92held against the lock 93.Fa lkp . 94.Pp 95The 96.Fn lockcountnb 97function is a non-blocking counter-part of 98.Fn lockcount . 99which, can be safely used in assertion statements e.g. a 100.Xr KASSERT 9 . 101.Pp 102The 103.Fn lockmgr 104function handles general locking functionality within the kernel, including 105support for shared and exclusive locks, and recursion. 106.Fn lockmgr 107is also able to upgrade and downgrade locks. 108.Pp 109Its arguments are: 110.Bl -tag -width ".Fa flags" 111.It Fa lkp 112A pointer to the lock to manipulate. 113.It Fa flags 114Flags indicating what action is to be taken. 115.Bl -tag -width ".Dv LK_EXCLUPGRADE" 116.It Dv LK_SHARED 117Acquire a shared lock. 118If an exclusive lock is currently held, it will be downgraded. 119.It Dv LK_EXCLUSIVE 120Acquire an exclusive lock. 121If an exclusive lock is already held, and 122.Dv LK_CANRECURSE 123is not set, the system will 124.Xr panic 9 . 125.It Dv LK_DOWNGRADE 126Downgrade exclusive lock to a shared lock. 127Downgrading a shared lock is not permitted. 128If an exclusive lock has been recursed, all references will be downgraded. 129.It Dv LK_EXCLUPGRADE 130Upgrade a shared lock to an exclusive lock. 131Fails with 132.Er EBUSY 133if there is someone ahead of you in line waiting for an upgrade. 134If this call fails, the shared lock is lost. 135Attempts to upgrade an exclusive lock will cause a 136.Xr panic 9 . 137.It Dv LK_UPGRADE 138Upgrade a shared lock to an exclusive lock. 139If this call fails, the shared lock is lost. 140Attempts to upgrade an exclusive lock will cause a 141.Xr panic 9 . 142.It Dv LK_RELEASE 143Release the lock. 144Releasing a lock that is not held can cause a 145.Xr panic 9 . 146.It Dv LK_SLEEPFAIL 147Fail if operation has slept. 148.It Dv LK_NOWAIT 149Do not allow the call to sleep. 150This can be used to test the lock. 151.It Dv LK_CANRECURSE 152Allow recursion on an exclusive lock. 153For every lock there must be a release. 154.El 155.El 156.Pp 157The 158.Fn lockstatus 159function returns the status of the lock in relation to the 160.Vt thread 161passed to it. 162Note that if 163.Fa td 164is 165.Dv NULL 166and an exclusive lock is held, 167.Dv LK_EXCLUSIVE 168will be returned. 169.Pp 170The 171.Fn lockmgr_printinfo 172function prints debugging information about the lock. 173It is used primarily by 174.Xr VOP_PRINT 9 175functions. 176.Sh RETURN VALUES 177The 178.Fn lockcount 179function returns an integer greater than or equal to zero. 180.Pp 181The 182.Fn lockmgr 183function returns 0 on success and non-zero on failure. 184.Pp 185The 186.Fn lockstatus 187function returns: 188.Bl -tag -width ".Dv LK_EXCLUSIVE" 189.It Dv LK_EXCLUSIVE 190An exclusive lock is held by the thread 191.Fa td . 192.It Dv LK_EXCLOTHER 193An exclusive lock is held by someone other than the thread 194.Fa td . 195.It Dv LK_SHARED 196A shared lock is held. 197.It Li 0 198The lock is not held by anyone. 199.El 200.Sh ERRORS 201.Fn lockmgr 202fails if: 203.Bl -tag -width Er 204.It Bq Er EBUSY 205.Dv LK_NOWAIT 206was set, and a sleep would have been required. 207.It Bq Er ENOLCK 208.Dv LK_SLEEPFAIL 209was set and 210.Fn lockmgr 211did sleep. 212.It Bq Er EINTR 213.Dv PCATCH 214was set in the lock priority, and a signal was delivered during a sleep. 215Note the 216.Er ERESTART 217error below. 218.It Bq Er ERESTART 219.Dv PCATCH 220was set in the lock priority, a signal was delivered during a sleep, 221and the system call is to be restarted. 222.It Bq Er EWOULDBLOCK 223a non-zero timeout was given, and the timeout expired. 224.El 225.Sh LOCKS 226Upgrade attempts that fail result in the loss of the lock that 227is currently held. 228Also, it is invalid to upgrade an 229exclusive lock, and a 230.Xr panic 9 231will be the result of trying. 232.Sh SEE ALSO 233.Xr panic 9 , 234.Xr tsleep 9 , 235.Xr VOP_PRINT 9 236.Sh AUTHORS 237This man page was written by 238.An Chad David Aq davidc@acns.ab.ca . 239