5385e8bfab
some content and layout changes were made. lock.9 had existed before but was never added to Makefile, so it was never installed. That is why the duplicate files were created in the first place. Reviewed by: ru, alfred
282 lines
7.3 KiB
Groff
282 lines
7.3 KiB
Groff
.\"
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.\" Copyright (C) 2002 Chad David <davidc@acns.ab.ca>. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
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.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
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.\" DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 9, 2001
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.Dt LOCK 9
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.Os
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.Sh NAME
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.Nm lockinit ,
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.Nm lockdestroy ,
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.Nm lockcount ,
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.Nm lockmgr ,
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.Nm lockstatus ,
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.Nm lockmgr_printinfo
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.Nd "lockmgr family of functions"
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/lockmgr.h
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.Ft void
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.Fn lockinit "struct lock *lkp" "int prio" "char *wmesg" "int timo" "int flags"
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.Ft void
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.Fn lockdestroy "struct lock *lkp"
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.Ft int
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.Fn lockcount "struct lock *lkp"
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.Ft int
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.Fn lockmgr "struct lock *lkp" "u_int flags" "struct mtx *interlkp" "struct thread *td"
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.Ft int
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.Fn lockstatus "struct lock *lkp" "struct thread *td"
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.Ft void
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.Fn lockmgr_printinfo "struct lock *lkp"
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.Sh DESCRIPTION
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The
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.Fn lockinit
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function is used to initialize a lock.
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It must be called prior to any operation could be performed on a lock.
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Its arguments are:
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.Bl -tag -width ".Fa wmesg"
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.It Fa lkp
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A pointer to the lock to initialize.
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.It Fa prio
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The priority passed to
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.Xr msleep 9 .
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.It Fa wmesg
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The lock message.
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This is used for both debugging output and
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.Xr msleep 9 .
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.It Fa timo
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The timeout value passed to
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.Xr msleep 9 .
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.It Fa flags
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The flags the lock is to be initialized with.
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.Bl -tag -width ".Dv LG_CANRECURSE"
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.It Dv LK_NOWAIT
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Do not sleep while acquiring the lock.
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.It Dv LK_SLEEPFAIL
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Fail after a sleep.
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.It Dv LK_CANRECURSE
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Allow recursive exclusive locks.
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.It Dv LK_REENABLE
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Re-enable the lock after a drain.
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.It Dv LK_NOPAUSE
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Disable the spinlock while acquiring the lock.
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.It Dv LK_TIMELOCK
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Use
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.Fa timo
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during a sleep; otherwise, 0 is used.
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.El
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.El
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.Pp
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The
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.Fn lockdestroy
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function is used to destroy a lock, and while it is called in a number of
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places in the kernel, it currently does nothing.
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.Pp
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The
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.Fn lockcount
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function returns a count of the number of exclusive locks and shared locks
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held against the lock
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.Fa lkp .
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.Pp
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The
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.Fn lockmgr
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function handles general locking functionality within the kernel, including
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support for shared and exclusive locks, and recursion.
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.Fn lockmgr
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is also able to upgrade and downgrade locks.
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.Pp
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Its arguments are:
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.Bl -tag -width ".Fa interlkp"
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.It Fa lkp
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A pointer to the lock to manipulate.
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.It Fa flags
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Flags indicating what action is to be taken.
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.Bl -tag -width ".Dv LK_EXCLUPGRADE"
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.It Dv LK_SHARED
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Acquire a shared lock.
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If an exclusive lock is currently held, it will be downgraded.
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.It Dv LK_EXCLUSIVE
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Acquire an exclusive lock.
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If an exclusive lock is already held, and
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.Dv LK_CANRECURSE
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is not set, the system will
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.Xr panic 9 .
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.It Dv LK_DOWNGRADE
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Downgrade exclusive lock to a shared lock.
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Downgrading a shared lock is not permitted.
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If an exclusive lock has been recursed, all references will be downgraded.
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.It Dv LK_EXCLUPGRADE
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Upgrade a shared lock to an exclusive lock.
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Fails with
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.Er EBUSY
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if there is someone ahead of use waiting for an upgrade.
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If this call fails, the shared lock is lost.
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Attempt to upgrade an exclusive lock will cause a
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.Xr panic 9 .
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.It Dv LK_UPGRADE
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Upgrade a shared lock to an exclusive lock.
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If this call fails, the shared lock is lost.
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Attempt to upgrade an exclusive lock will cause a
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.Xr panic 9 .
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.It Dv LK_RELEASE
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Release the lock.
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Releasing a lock that is not held can cause a
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.Xr panic 9 .
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.It Dv LK_DRAIN
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Wait for all activity on the lock to end, then mark it decommissioned.
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This is used before freeing a lock that is part of a piece of memory that is
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about to be freed.
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(As documented in
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.Aq Pa sys/lockmgr.h . )
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.It Dv LK_SLEEPFAIL
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Fail if operation has slept.
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.It Dv LK_NOWAIT
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Do not allow the call to sleep.
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This can be used to test the lock.
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.It Dv LK_CANRECURSE
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Allow recursion on an exclusive lock.
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For every lock there must be a release.
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.It Dv LK_INTERLOCK
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Unlock the interlock (which should be locked already).
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.El
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.It Fa interlkp
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An interlock mutex for controlling group access to the lock.
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If
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.Dv LK_INTERLOCK
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is specified,
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.Fn lockmgr
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assumes
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.Fa interlkp
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is currently owned and not recursed, and will return it unlocked.
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See
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.Xr mtx_assert 9 .
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.It Fa td
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A thread responsible for this call.
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.Dv NULL
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becomes
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.Dv LK_KERNPROC .
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.El
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.Pp
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The
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.Fn lockstatus
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function returns the status of the lock in relation to the
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.Vt thread
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passed to it.
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Note that if
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.Fa td
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is
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.Dv NULL
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and an exclusive lock is held,
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.Dv LK_EXCLUSIVE
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will be returned.
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.Pp
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The
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.Fn lockmgr_printinfo
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function prints debugging information about the lock.
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It is used primarily by
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.Xr VOP_PRINT 9
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functions.
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.Sh RETURN VALUES
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The
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.Fn lockcount
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function returns an integer greater than or equal to zero.
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.Pp
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The
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.Fn lockmgr
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function returns 0 on success and non-zero on failure.
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.Pp
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The
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.Fn lockstatus
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function returns:
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.Bl -tag -width ".Dv LK_EXCLUSIVE"
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.It Dv LK_EXCLUSIVE
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An exclusive lock is held by the thread
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.Fa td .
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.It Dv LK_EXCLOTHER
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An exclusive lock is held by someone other than the thread
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.Fa td .
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.It Dv LK_SHARED
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A shared lock is held.
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.It Li 0
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The lock is not held by anyone.
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.El
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.Sh ERRORS
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.Fn lockmgr
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fails if:
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.Bl -tag -width Er
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.It Bq Er EBUSY
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.Dv LK_FORCEUPGRADE
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was requested and another thread had already requested a lock upgrade.
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.It Bq Er EBUSY
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.Dv LK_NOWAIT
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was set, and a sleep would have been required.
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.It Bq Er ENOLCK
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.Dv LK_SLEEPFAIL
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was set and
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.Fn lockmgr
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did sleep.
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.It Bq Er EINTR
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.Dv PCATCH
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was set in the lock priority, and a signal was delivered during a sleep.
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Note the
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.Er ERESTART
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error below.
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.It Bq Er ERESTART
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.Dv PCATCH
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was set in the lock priority, a signal was delivered during a sleep,
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and the system call is to be restarted.
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.It Bq Er EWOULDBLOCK
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a non-zero timeout was given, and the timeout expired.
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.El
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.Sh LOCKS
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If
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.Dv LK_INTERLOCK
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is passed in the
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.Fa flags
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argument to
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.Fn lockmgr ,
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the
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.Fa interlkp
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must be held prior to calling
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.Fn lockmgr ,
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and will be returned unlocked.
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.Pp
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Upgrade attempts that fail result in the loss of the lock that
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is currently held.
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Also, it is invalid to upgrade an
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exclusive lock, and a
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.Xr panic 9
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will be the result of trying.
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.Sh SEE ALSO
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.Xr msleep 9 ,
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.Xr mtx_assert 9 ,
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.Xr panic 9 ,
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.Xr VOP_PRINT 9
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.Sh AUTHORS
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This man page was written by
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.An Chad David Aq davidc@acns.ab.ca .
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