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.\" 29.Dd July 26, 2010 30.Dt LOCK 9 31.Os 32.Sh NAME 33.Nm lockinit , 34.Nm lockcount , 35.Nm lockmgr , 36.Nm lockstatus , 37.Nm lockmgr_printinfo 38.Nd "lockmgr family of functions" 39.Sh SYNOPSIS 40.In sys/types.h 41.In sys/lock.h 42.Ft void 43.Fn lockinit "struct lock *lkp" "const char *wmesg" "int timo" "int flags" 44.Ft void 45.Fn lockuninit "struct lock *lkp" 46.Ft int 47.Fn lockcount "struct lock *lkp" 48.Ft int 49.Fn lockcountnb "struct lock *lkp" 50.Ft int 51.Fn lockmgr "struct lock *lkp" "u_int flags" 52.Ft int 53.Fn lockstatus "struct lock *lkp" "struct thread *td" 54.Ft void 55.Fn lockmgr_printinfo "struct lock *lkp" 56.Sh DESCRIPTION 57The 58.Fn lockinit 59function is used to initialize a lock. 60It must be called before any operation can be performed on a lock. 61Its arguments are: 62.Bl -tag -width ".Fa wmesg" 63.It Fa lkp 64A pointer to the lock to initialize. 65.It Fa wmesg 66The lock message. 67This is used for both debugging output and 68.Xr tsleep 9 . 69.It Fa timo 70The timeout value passed to 71.Xr tsleep 9 . 72.It Fa flags 73The flags the lock is to be initialized with. 74.Bl -tag -width ".Dv LK_CANRECURSE" 75.It Dv LK_NOWAIT 76Do not sleep while acquiring the lock. 77.It Dv LK_SLEEPFAIL 78Fail after a sleep. 79.It Dv LK_CANRECURSE 80Allow recursive exclusive locks. 81.It Dv LK_TIMELOCK 82Use 83.Fa timo 84during a sleep; otherwise, 0 is used. 85.El 86.El 87.Pp 88The 89.Fn lockuninit 90function destroys a lock that was previously initialized using 91.Fn lockinit . 92.Pp 93The 94.Fn lockcount 95function returns a count of the number of exclusive locks and shared locks 96held against the lock 97.Fa lkp . 98.Pp 99The 100.Fn lockcountnb 101function is a non-blocking counter-part of 102.Fn lockcount . 103which, can be safely used in assertion statements e.g. a 104.Xr KASSERT 9 . 105.Pp 106The 107.Fn lockmgr 108function handles general locking functionality within the kernel, including 109support for shared and exclusive locks, and recursion. 110.Fn lockmgr 111is also able to upgrade and downgrade locks. 112.Pp 113Its arguments are: 114.Bl -tag -width ".Fa flags" 115.It Fa lkp 116A pointer to the lock to manipulate. 117.It Fa flags 118Flags indicating what action is to be taken. 119.Bl -tag -width ".Dv LK_EXCLUPGRADE" 120.It Dv LK_SHARED 121Acquire a shared lock. 122If an exclusive lock is currently held, it will be downgraded. 123.It Dv LK_EXCLUSIVE 124Acquire an exclusive lock. 125If an exclusive lock is already held, and 126.Dv LK_CANRECURSE 127is not set, the system will 128.Xr panic 9 . 129.It Dv LK_DOWNGRADE 130Downgrade exclusive lock to a shared lock. 131Downgrading a shared lock is not permitted. 132If an exclusive lock has been recursed, all references will be downgraded. 133.It Dv LK_EXCLUPGRADE 134Upgrade a shared lock to an exclusive lock. 135Fails with 136.Er EBUSY 137if there is someone ahead of you in line waiting for an upgrade. 138If this call fails, the shared lock is lost. 139Attempts to upgrade an exclusive lock will cause a 140.Xr panic 9 . 141.It Dv LK_UPGRADE 142Upgrade a shared lock to an exclusive lock. 143If this call fails, the shared lock is lost. 144Attempts to upgrade an exclusive lock will cause a 145.Xr panic 9 . 146.It Dv LK_RELEASE 147Release the lock. 148Releasing a lock that is not held can cause a 149.Xr panic 9 . 150.It Dv LK_SLEEPFAIL 151Fail if operation has slept. 152.It Dv LK_NOWAIT 153Do not allow the call to sleep. 154This can be used to test the lock. 155.It Dv LK_CANRECURSE 156Allow recursion on an exclusive lock. 157For every lock there must be a release. 158.El 159.El 160.Pp 161The 162.Fn lockstatus 163function returns the status of the lock in relation to the 164.Vt thread 165passed to it. 166Note that if 167.Fa td 168is 169.Dv NULL 170and an exclusive lock is held, 171.Dv LK_EXCLUSIVE 172will be returned. 173.Pp 174The 175.Fn lockmgr_printinfo 176function prints debugging information about the lock. 177It is used primarily by 178.Xr VOP_PRINT 9 179functions. 180.Sh RETURN VALUES 181The 182.Fn lockcount 183function returns an integer greater than or equal to zero. 184.Pp 185The 186.Fn lockmgr 187function returns 0 on success and non-zero on failure. 188.Pp 189The 190.Fn lockstatus 191function returns: 192.Bl -tag -width ".Dv LK_EXCLUSIVE" 193.It Dv LK_EXCLUSIVE 194An exclusive lock is held by the thread 195.Fa td . 196.It Dv LK_EXCLOTHER 197An exclusive lock is held by someone other than the thread 198.Fa td . 199.It Dv LK_SHARED 200A shared lock is held. 201.It Li 0 202The lock is not held by anyone. 203.El 204.Sh FILES 205The lock manager itself is implemented within the file 206.Pa /sys/kern/kern_lock.c . 207Data structures and function prototypes for the lock manager are in 208.Pa /sys/sys/lock.h . 209.Sh ERRORS 210.Fn lockmgr 211fails if: 212.Bl -tag -width Er 213.It Bq Er EBUSY 214.Dv LK_NOWAIT 215was set, and a sleep would have been required. 216.It Bq Er ENOLCK 217.Dv LK_SLEEPFAIL 218was set and 219.Fn lockmgr 220did sleep. 221.It Bq Er EINTR 222.Dv PCATCH 223was set in the lock priority, and a signal was delivered during a sleep. 224Note the 225.Er ERESTART 226error below. 227.It Bq Er ERESTART 228.Dv PCATCH 229was set in the lock priority, a signal was delivered during a sleep, 230and the system call is to be restarted. 231.It Bq Er EWOULDBLOCK 232a non-zero timeout was given, and the timeout expired. 233.El 234.Sh LOCKS 235Upgrade attempts that fail result in the loss of the lock that 236is currently held. 237Also, it is invalid to upgrade an 238exclusive lock, and a 239.Xr panic 9 240will be the result of trying. 241.Sh SEE ALSO 242.Xr panic 9 , 243.Xr tsleep 9 , 244.Xr VOP_PRINT 9 245.Sh HISTORY 246The lock manager appeared in 247.Dx 1.0 . 248.Pp 249The lock manager API first appeared in 250.Bx 4.4 lite2 . 251.Sh AUTHORS 252This man page was written by 253.An Chad David Aq davidc@acns.ab.ca . 254