fb5c76c176
mlock, mmap, mprotect, msync, munlock, and munmap are defined by POSIX as taking void *. The const modifier has been added to mlock, munlock, and mprotect as the standard dictates. minherit comes from OpenBSD and has been updated to conform with their recent change to void *. madvise and mincore are not defined by POSIX, but their arguments have been modified to be consistent with the POSIX-defined functions. mincore takes a const pointer, but madvise does not due to the MADV_FREE case. Discussed with: bde
163 lines
5.3 KiB
Groff
163 lines
5.3 KiB
Groff
.\" Copyright (c) 1993
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.\" The Regents of the University of California. 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, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, 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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER 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
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)mlock.2 8.2 (Berkeley) 12/11/93
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.\"
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.Dd June 2, 1993
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.Dt MLOCK 2
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.Os
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.Sh NAME
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.Nm mlock ,
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.Nm munlock
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.Nd lock (unlock) physical pages in memory
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/mman.h>
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.Ft int
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.Fn mlock "const void *addr" "size_t len"
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.Ft int
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.Fn munlock "const void *addr" "size_t len"
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.Sh DESCRIPTION
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The
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.Fn mlock
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system call
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locks into memory the physical pages associated with the virtual address
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range starting at
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.Fa addr
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for
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.Fa len
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bytes.
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The
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.Fn munlock
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call unlocks pages previously locked by one or more
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.Fn mlock
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calls.
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For both, the
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.Fa addr
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parameter should be aligned to a multiple of the page size.
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If the
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.Fa len
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parameter is not a multiple of the page size, it will be rounded up
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to be so.
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The entire range must be allocated.
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.Pp
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After an
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.Fn mlock
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call, the indicated pages will cause neither a non-resident page
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nor address-translation fault until they are unlocked.
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They may still cause protection-violation faults or TLB-miss faults on
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architectures with software-managed TLBs.
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The physical pages remain in memory until all locked mappings for the pages
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are removed.
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Multiple processes may have the same physical pages locked via their own
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virtual address mappings.
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A single process may likewise have pages multiply-locked via different virtual
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mappings of the same pages or via nested
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.Fn mlock
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calls on the same address range.
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Unlocking is performed explicitly by
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.Fn munlock
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or implicitly by a call to
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.Fn munmap
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which deallocates the unmapped address range.
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Locked mappings are not inherited by the child process after a
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.Xr fork 2 .
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.Pp
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Since physical memory is a potentially scarce resource, processes are
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limited in how much they can lock down.
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A single process can
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.Fn mlock
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the minimum of
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a system-wide ``wired pages'' limit and
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the per-process
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.Li RLIMIT_MEMLOCK
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resource limit.
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.Sh RETURN VALUES
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A return value of 0 indicates that the call
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succeeded and all pages in the range have either been locked or unlocked.
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A return value of -1 indicates an error occurred and the locked
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status of all pages in the range remains unchanged.
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In this case, the global location
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn Mlock
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The address given is not page aligned or the length is negative.
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.It Bq Er EAGAIN
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Locking the indicated range would exceed either the system or per-process
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limit for locked memory.
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.It Bq Er ENOMEM
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Some portion of the indicated address range is not allocated.
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There was an error faulting/mapping a page.
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.El
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.Fn Munlock
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The address given is not page aligned or the length is negative.
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.It Bq Er ENOMEM
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Some portion of the indicated address range is not allocated.
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Some portion of the indicated address range is not locked.
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.El
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.Sh "SEE ALSO"
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.Xr fork 2 ,
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.Xr mmap 2 ,
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.Xr munmap 2 ,
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.Xr setrlimit 2 ,
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.Xr getpagesize 3
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.Sh BUGS
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Unlike The Sun implementation, multiple
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.Fn mlock
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calls on the same address range require the corresponding number of
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.Fn munlock
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calls to actually unlock the pages, i.e.
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.Fn mlock
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nests.
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This should be considered a consequence of the implementation
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and not a feature.
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.Pp
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The per-process resource limit is a limit on the amount of virtual
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memory locked, while the system-wide limit is for the number of locked
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physical pages.
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Hence a process with two distinct locked mappings of the same physical page
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counts as 2 pages against the per-process limit and as only a single page
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in the system limit.
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.Sh HISTORY
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The
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.Fn mlock
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and
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.Fn munlock
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functions first appeared in
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.Bx 4.4 .
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