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 1.6 2007/04/05 20:01:19 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_TIMELOCK 81Use 82.Fa timo 83during a sleep; otherwise, 0 is used. 84.El 85.El 86.Pp 87The 88.Fn lockcount 89function returns a count of the number of exclusive locks and shared locks 90held against the lock 91.Fa lkp . 92.Pp 93The 94.Fn lockcountnb 95function is a non-blocking counter-part of 96.Fn lockcount . 97which, can be safely used in assertion statements e.g. a 98.Xr KASSERT 9 . 99.Pp 100The 101.Fn lockmgr 102function handles general locking functionality within the kernel, including 103support for shared and exclusive locks, and recursion. 104.Fn lockmgr 105is also able to upgrade and downgrade locks. 106.Pp 107Its arguments are: 108.Bl -tag -width ".Fa flags" 109.It Fa lkp 110A pointer to the lock to manipulate. 111.It Fa flags 112Flags indicating what action is to be taken. 113.Bl -tag -width ".Dv LK_EXCLUPGRADE" 114.It Dv LK_SHARED 115Acquire a shared lock. 116If an exclusive lock is currently held, it will be downgraded. 117.It Dv LK_EXCLUSIVE 118Acquire an exclusive lock. 119If an exclusive lock is already held, and 120.Dv LK_CANRECURSE 121is not set, the system will 122.Xr panic 9 . 123.It Dv LK_DOWNGRADE 124Downgrade exclusive lock to a shared lock. 125Downgrading a shared lock is not permitted. 126If an exclusive lock has been recursed, all references will be downgraded. 127.It Dv LK_EXCLUPGRADE 128Upgrade a shared lock to an exclusive lock. 129Fails with 130.Er EBUSY 131if there is someone ahead of you in line waiting for an upgrade. 132If this call fails, the shared lock is lost. 133Attempts to upgrade an exclusive lock will cause a 134.Xr panic 9 . 135.It Dv LK_UPGRADE 136Upgrade a shared lock to an exclusive lock. 137If this call fails, the shared lock is lost. 138Attempts to upgrade an exclusive lock will cause a 139.Xr panic 9 . 140.It Dv LK_RELEASE 141Release the lock. 142Releasing a lock that is not held can cause a 143.Xr panic 9 . 144.It Dv LK_SLEEPFAIL 145Fail if operation has slept. 146.It Dv LK_NOWAIT 147Do not allow the call to sleep. 148This can be used to test the lock. 149.It Dv LK_CANRECURSE 150Allow recursion on an exclusive lock. 151For every lock there must be a release. 152.El 153.El 154.Pp 155The 156.Fn lockstatus 157function returns the status of the lock in relation to the 158.Vt thread 159passed to it. 160Note that if 161.Fa td 162is 163.Dv NULL 164and an exclusive lock is held, 165.Dv LK_EXCLUSIVE 166will be returned. 167.Pp 168The 169.Fn lockmgr_printinfo 170function prints debugging information about the lock. 171It is used primarily by 172.Xr VOP_PRINT 9 173functions. 174.Sh RETURN VALUES 175The 176.Fn lockcount 177function returns an integer greater than or equal to zero. 178.Pp 179The 180.Fn lockmgr 181function returns 0 on success and non-zero on failure. 182.Pp 183The 184.Fn lockstatus 185function returns: 186.Bl -tag -width ".Dv LK_EXCLUSIVE" 187.It Dv LK_EXCLUSIVE 188An exclusive lock is held by the thread 189.Fa td . 190.It Dv LK_EXCLOTHER 191An exclusive lock is held by someone other than the thread 192.Fa td . 193.It Dv LK_SHARED 194A shared lock is held. 195.It Li 0 196The lock is not held by anyone. 197.El 198.Sh ERRORS 199.Fn lockmgr 200fails if: 201.Bl -tag -width Er 202.It Bq Er EBUSY 203.Dv LK_NOWAIT 204was set, and a sleep would have been required. 205.It Bq Er ENOLCK 206.Dv LK_SLEEPFAIL 207was set and 208.Fn lockmgr 209did sleep. 210.It Bq Er EINTR 211.Dv PCATCH 212was set in the lock priority, and a signal was delivered during a sleep. 213Note the 214.Er ERESTART 215error below. 216.It Bq Er ERESTART 217.Dv PCATCH 218was set in the lock priority, a signal was delivered during a sleep, 219and the system call is to be restarted. 220.It Bq Er EWOULDBLOCK 221a non-zero timeout was given, and the timeout expired. 222.El 223.Sh LOCKS 224Upgrade attempts that fail result in the loss of the lock that 225is currently held. 226Also, it is invalid to upgrade an 227exclusive lock, and a 228.Xr panic 9 229will be the result of trying. 230.Sh SEE ALSO 231.Xr panic 9 , 232.Xr tsleep 9 , 233.Xr VOP_PRINT 9 234.Sh AUTHORS 235This man page was written by 236.An Chad David Aq davidc@acns.ab.ca . 237