Differences between current version and previous revision of munmap(2).
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| Newer page: | version 5 | Last edited on Saturday, March 15, 2003 1:45:02 am | by PerryLorier | |
| Older page: | version 4 | Last edited on Tuesday, June 4, 2002 12:23:43 am | by perry | Revert |
@@ -1,215 +1,67 @@
-MMAP
-!!!MMAP
-NAME
-SYNOPSIS
-DESCRIPTION
-RETURN VALUE
-ERRORS
-CONFORMING TO
-SEE ALSO
-----
!!NAME
-
mmap, munmap - map or unmap files or devices into memory
+
!!SYNOPSIS
+ __#include <unistd.h>__
+ __#include <sys/mman.h>__
+ __#ifdef _POSIX_MAPPED_FILES__
-__#include
__
-#include
__
+
__void * mmap(void *
__''start''__, size_t__ ''length''__, int__ ''prot'' __, int__ ''flags''__, int__ ''fd''__, off_t__ ''offset''__);
__
+ __int munmap(void *__''start''__, size_t__ ''length''__);__
-__#ifdef _POSIX_MAPPED_FILES
__
+
__#endif
__
-
-__void * mmap(void *__''start''__, size_t__
-''length''__, int__ ''prot'' __, int__
-''flags''__, int__ ''fd''__, off_t__
-''offset''__);__
-
-
-__int munmap(void *__''start''__, size_t__
-''length''__);__
-
-
-__#endif__
!!DESCRIPTION
+The __mmap__ function asks to map ''length'' bytes starting at offset ''offset'' from the file (or other object) specified by the file descriptor ''fd'' into memory, preferably at address ''start''. This latter address is a hint only, and is usually specified as 0. The actual place where the object is mapped is returned by __mmap__. The ''prot'' argument describes the desired memory protection (and must not conflict with the open mode of the file). It has bits
+;__PROT_EXEC__: Pages may be executed.
+;__PROT_READ__: Pages may be read.
+;__PROT_WRITE__: Pages may be written.
+;__PROT_NONE__: Pages may not be accessed.
-The __mmap__ function asks to map
''length
'' bytes
-starting at offset ''offset'' from
the file (or other
-) specified by the file descriptor ''fd'' into
-memory, preferably at address ''start''. This latter
-address is a hint only
, and is usually specified as . The
-actual place where
the object is
mapped is returned by
-__mmap__. The ''prot'' argument describes
the desired
-memory protection (and must not conflict
with the open mode
-of the file)
. It has bits
+The ''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
. It has bits
+;__MAP_FIXED__: Do not select a different address than the one specified. If the specified address cannot be used, __mmap__ will fail. If MAP_FIXED is specified, ''start'' must be a multiple of the pagesize. Use of this option is discouraged.
-__PROT
_EXEC
__
+;
__MAP
_SHARED
__: Share this mapping with all other processes that map this object. Storing to the region is equivalent to writing to the file. The file may not actually be updated until msync(2) or munmap(2) are called.
+;__MAP_PRIVATE__: Create a private copy-on-write mapping. Stores to the region do not affect the original file.
-Pages may be executed
.
+You must specify exactly one of MAP_SHARED and MAP_PRIVATE
.
-
-__PROT_READ__
-
-
-Pages may be read.
-
-
-__PROT_WRITE__
-
-
-Pages may be written.
-
-
-__PROT_NONE__
-
-
-Pages may not be accessed.
-
-
-The ''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. It has
-bits
-
-
-__MAP_FIXED__
-
-
-Do not select a different address than the one specified. If
-the specified address cannot be used, __mmap__ will fail.
-If MAP_FIXED is specified, ''start'' must be a multiple
-of the pagesize. Use of this option is
-discouraged.
-
-
-__MAP_SHARED__
-
-
-Share this mapping with all other processes that map this
-object. Storing to the region is equivalent to writing to
-the file. The file may not actually be updated until
-msync(2) or munmap(2) are called.
-
-
-__MAP_PRIVATE__
-
-
-Create a private copy-on-write mapping. Stores to the region
-do not affect the original file.
-
-
-You must specify exactly one of MAP_SHARED and
-MAP_PRIVATE.
-
-
-
-
-
+The above three flags are described in POSIX.1b (formerly POSIX.4). Linux also knows about MAP_DENYWRITE, MAP_EXECUTABLE, MAP_NORESERVE, MAP_LOCKED, MAP_GROWSDOWN and
MAP_ANON(YMOUS).
+''offset'' should ordinarily be a multiple of the page size returned by getpagesize(2).
-''offset'' should ordinarily be a multiple of the page
-size returned
by getpagesize
(2).
+Memory mapped
by __mmap__ is preserved across fork
(2), with the same attributes
.
+The __munmap__ system call deletes the mappings for the specified address range, and causes further references to addresses within the range to generate invalid memory
+references. The region is also automatically unmapped when the process is terminated. On the other hand, closing the file descriptor does not unmap the region.
-Memory mapped by __mmap__ is preserved across
-fork(2), with the same attributes.
-
-
-The __munmap__ system call deletes the mappings for the
-specified address range, and causes further references to
-addresses within the range to generate invalid memory
-references. The region is also automatically unmapped when
-the process is terminated. On the other hand, closing the
-file descriptor does not unmap the region.
!!RETURN VALUE
-
-
-
-
-
-returns , on failure -1, and ''errno'' is set (probably
-
+On success, __mmap__ returns a pointer to the mapped area. On error, MAP_FAILED (-1) is returned, and ''errno'' is set appropriately. On success, __munmap__
+returns , on failure -1, and ''errno'' is set (probably to [
EINVAL]
).
!!ERRORS
-
-__
EBADF__
-
-
-
-
-
-
-__
EACCES__
-
-
-
-
-
+;[
EBADF]:
''fd'' is not a valid file descriptor (and MAP_ANONYMOUS was not set).
+;[
EACCES]:
MAP_PRIVATE was requested, but ''fd'' is not open for reading. Or MAP_SHARED was requested and PROT_WRITE is set, but ''fd'' is not open in read/write (O_RDWR)
mode.
+;[EINVAL]: We don't like ''start'' or ''length'' or ''offset''. (E.g., they are too large, or not aligned on a PAGESIZE boundary.)
+;[ETXTBSY]: MAP_DENYWRITE was set but the object specified by ''fd'' is open for writing.
+;[EAGAIN]: The file has been locked, or too much memory has been locked.
+;[ENOMEM]: No memory is available.
+Use of a mapped region can result in these signals:
-__EINVAL__
+;[SIGSEGV]: Attempted write into a region specified to mmap as read-only.
+;[SIGBUS]: Attempted access to a portion of the buffer that does not correspond to the file (for example, beyond the end of the file, including the case where another process has truncated the file).
-
-We don't like ''start'' or ''length'' or
-''offset''. (E.g., they are too large, or not aligned on
-a PAGESIZE boundary.)
-
-
-__ETXTBSY__
-
-
-MAP_DENYWRITE was set but the object specified by ''fd''
-is open for writing.
-
-
-__EAGAIN__
-
-
-The file has been locked, or too much memory has been
-locked.
-
-
-__ENOMEM__
-
-
-No memory is available.
-
-
-Use of a mapped region can result in these
-signals:
-
-
-__SIGSEGV__
-
-
-Attempted write into a region specified to mmap as
-read-only.
-
-
-__SIGBUS__
-
-
-Attempted access to a portion of the buffer that does not
-correspond to the file (for example, beyond the end of the
-file, including the case where another process has truncated
-the file).
!!CONFORMING TO
+SVr4, POSIX.1b (formerly POSIX.4), 4.4BSD. Svr4 documents additional error codes ENXIO and ENODEV.
-
-SVr4, POSIX.1b (formerly POSIX.4), 4.4BSD. Svr4 documents
-additional error codes ENXIO and ENODEV.
!!SEE ALSO
-
-
-
-
-
-----
+getpagesize(2), msync(2), shm_open(2), B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.
