299 lines
7.7 KiB
Groff
299 lines
7.7 KiB
Groff
.\" $NetBSD: mmap.2,v 1.36 2004/03/24 16:14:36 wiz Exp $
|
|
.\"
|
|
.\" Copyright (c) 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)mmap.2 8.4 (Berkeley) 5/11/95
|
|
.\"
|
|
.Dd October 6, 2003
|
|
.Dt MMAP 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm mmap
|
|
.Nd map files or devices into memory
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In sys/mman.h
|
|
.Ft void *
|
|
.Fn mmap "void *addr" "size_t len" "int prot" "int flags" "int fd" "off_t offset"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm mmap
|
|
function causes the pages starting at
|
|
.Fa addr
|
|
and continuing for at most
|
|
.Fa len
|
|
bytes to be mapped from the object described by
|
|
.Fa fd ,
|
|
starting at byte offset
|
|
.Fa offset .
|
|
If
|
|
.Fa len
|
|
is not a multiple of the pagesize, the mapped region may extend past the
|
|
specified range.
|
|
Any such extension beyond the end of the mapped object will be zero-filled.
|
|
.Pp
|
|
If
|
|
.Fa addr
|
|
is non-zero, it is used as a hint to the system.
|
|
(As a convenience to the system, the actual address of the region may differ
|
|
from the address supplied.)
|
|
If
|
|
.Fa addr
|
|
is zero, an address will be selected by the system.
|
|
The actual starting address of the region is returned.
|
|
A successful
|
|
.Fa mmap
|
|
deletes any previous mapping in the allocated address range.
|
|
.Pp
|
|
The protections (region accessibility) are specified in the
|
|
.Fa prot
|
|
argument by
|
|
.Em or Ns 'ing
|
|
the following values:
|
|
.Pp
|
|
.Bl -tag -width PROT_WRITEXX
|
|
.It Dv PROT_EXEC
|
|
Pages may be executed.
|
|
.It Dv PROT_READ
|
|
Pages may be read.
|
|
.It Dv PROT_WRITE
|
|
Pages may be written.
|
|
.It Dv PROT_NONE
|
|
Pages may not be accessed.
|
|
.El
|
|
.Pp
|
|
.Bf -symbolic
|
|
Note that, due to hardware limitations, on some platforms
|
|
.Dv PROT_WRITE
|
|
may imply
|
|
.Dv PROT_READ ,
|
|
and
|
|
.Dv PROT_READ
|
|
may imply
|
|
.Dv PROT_EXEC .
|
|
Portable programs should not rely on these flags being separately
|
|
enforceable.
|
|
.Ef
|
|
.Pp
|
|
The
|
|
.Fa flags
|
|
parameter specifies the type of the mapped object, mapping options and
|
|
whether modifications made to the mapped copy of the page are private
|
|
to the process or are to be shared with other references.
|
|
Note that either
|
|
.Dv MAP_SHARED ,
|
|
.Dv MAP_PRIVATE
|
|
or
|
|
.Dv MAP_COPY
|
|
must be specified.
|
|
Sharing, mapping type and options are specified in the
|
|
.Fa flags
|
|
argument by
|
|
.Em or Ns 'ing
|
|
the following values:
|
|
.Pp
|
|
.Bl -tag -width MAP_HASSEMAPHOREXX
|
|
.It Dv MAP_ALIGNED(n)
|
|
Request that the allocation be aligned to the given boundary.
|
|
The parameter
|
|
.Ar n
|
|
should be the base 2 logarithm of the desired alignment (e.g., to
|
|
request alignment to 16K, use 14 as the value for n).
|
|
The alignment must be equal to or greater than the platform's page
|
|
size as returned by
|
|
.Xr sysconf 3
|
|
with the
|
|
.Dv _SC_PAGESIZE
|
|
request.
|
|
.It Dv MAP_ANON
|
|
Map anonymous memory not associated with any specific file.
|
|
The file descriptor is not used for creating
|
|
.Dv MAP_ANON
|
|
regions, and must be specified as \-1.
|
|
.It Dv MAP_FILE
|
|
Mapped from a regular file or character-special device memory.
|
|
.It Dv MAP_FIXED
|
|
Do not permit the system to select a different address than the one
|
|
specified.
|
|
If the specified address cannot be used,
|
|
.Nm mmap
|
|
will fail.
|
|
If MAP_FIXED is specified,
|
|
.Fa addr
|
|
must be a multiple of the pagesize.
|
|
Use of this option is discouraged.
|
|
.It Dv MAP_HASSEMAPHORE
|
|
Notify the kernel that the region may contain semaphores and that special
|
|
handling may be necessary.
|
|
.It Dv MAP_INHERIT
|
|
Permit regions to be inherited across
|
|
.Xr execve 2
|
|
system calls.
|
|
.It Dv MAP_TRYFIXED
|
|
Attempt to use the address
|
|
.Fa addr
|
|
even if it falls within the normally protected process data or
|
|
text segment memory regions. If the requested region of memory
|
|
is actually present in the memory map, a different address will
|
|
be selected as if MAP_TRYFIXED had not been specified. If
|
|
.Fa addr
|
|
is
|
|
.Fa NULL ,
|
|
this flag is ignored and the system will select a mapping address.
|
|
.It Dv MAP_WIRED
|
|
Lock the mapped region into memory as with
|
|
.Xr mlock 2 .
|
|
.It Dv MAP_PRIVATE
|
|
Modifications made by this process are private, however modifications made by
|
|
other processes using
|
|
.Dv MAP_SHARED
|
|
will be seen.
|
|
.It Dv MAP_SHARED
|
|
Modifications are shared.
|
|
.It Dv MAP_COPY
|
|
Modifications are private, including other processes.
|
|
.El
|
|
.Pp
|
|
The
|
|
.Xr close 2
|
|
function does not unmap pages, see
|
|
.Xr munmap 2
|
|
for further information.
|
|
.Pp
|
|
The current design does not allow a process to specify the location of
|
|
swap space.
|
|
In the future we may define an additional mapping type,
|
|
.Dv MAP_SWAP ,
|
|
in which
|
|
the file descriptor argument specifies a file or device to which swapping
|
|
should be done.
|
|
.Pp
|
|
If
|
|
.Dv MAP_FIXED
|
|
is not specified, the system will attempt to place the mapping in an
|
|
unused portion of the address space chosen to minimize possible
|
|
collision between mapped regions and the heap.
|
|
.Sh RETURN VALUES
|
|
Upon successful completion,
|
|
.Nm mmap
|
|
returns a pointer to the mapped region.
|
|
Otherwise, a value of
|
|
.Dv MAP_FAILED
|
|
is returned and
|
|
.Va errno
|
|
is set to indicate the error.
|
|
The symbol
|
|
.Dv MAP_FAILED
|
|
is defined in the header
|
|
.Ao Pa sys/mman.h Ac .
|
|
No successful return from
|
|
.Fn mmap
|
|
will return the value
|
|
.Dv MAP_FAILED .
|
|
.Sh ERRORS
|
|
.Fn mmap
|
|
will fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EACCES
|
|
The flag
|
|
.Dv PROT_READ
|
|
was specified as part of the
|
|
.Fa prot
|
|
parameter and
|
|
.Fa fd
|
|
was not open for reading.
|
|
The flags
|
|
.Dv MAP_SHARED
|
|
and
|
|
.Dv PROT_WRITE
|
|
were specified as part of the
|
|
.Fa flags
|
|
and
|
|
.Fa prot
|
|
parameters and
|
|
.Fa fd
|
|
was not open for writing.
|
|
.It Bq Er EBADF
|
|
.Fa fd
|
|
is not a valid open file descriptor.
|
|
.It Bq Er EINVAL
|
|
.\"One of
|
|
.\".Dv MAP_ANON
|
|
.\"or
|
|
.\".Dv MAP_FILE
|
|
.\"was not specified as part of the
|
|
.\".Fa flags
|
|
.\"parameter.
|
|
.Dv MAP_FIXED
|
|
was specified and the
|
|
.Fa addr
|
|
parameter was not page aligned or was outside of the
|
|
valid address range for a process.
|
|
.Dv MAP_ANON was specified and
|
|
.Fa fd
|
|
was not \-1.
|
|
.Fa len
|
|
was less than zero.
|
|
.It Bq Er ENODEV
|
|
.Fa fd
|
|
did not reference a regular or character special file.
|
|
.It Bq Er ENOMEM
|
|
.Dv MAP_FIXED
|
|
was specified and the
|
|
.Fa addr
|
|
parameter wasn't available.
|
|
.Dv MAP_ANON
|
|
was specified and insufficient memory was available.
|
|
.It Bq Er EOVERFLOW
|
|
.Fa fd
|
|
references a regular file and the value of
|
|
.Fa offset
|
|
plus
|
|
.Fa len
|
|
would exceed the offset maximum established in its open file description.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr madvise 2 ,
|
|
.Xr mincore 2 ,
|
|
.Xr mlock 2 ,
|
|
.Xr mprotect 2 ,
|
|
.Xr msync 2 ,
|
|
.Xr munmap 2 ,
|
|
.Xr getpagesize 3 ,
|
|
.Xr sysconf 3
|
|
.Sh BUGS
|
|
The
|
|
.Dv MAP_COPY
|
|
flag is not implemented.
|
|
The current
|
|
.Dv MAP_COPY
|
|
semantics are the same as those of the
|
|
.Dv MAP_PRIVATE
|
|
flag.
|