-.\" $NetBSD: mmap.2,v 1.5 1995/06/24 10:48:59 cgd Exp $
-.\"
.\" Copyright (c) 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" 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. All advertising materials mentioning features or use of this software
-.\" must display the following acknowledgement:
-.\" This product includes software developed by the University of
-.\" California, Berkeley and its contributors.
.\" 4. 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.
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
-.\" @(#)mmap.2 8.1 (Berkeley) 6/4/93
+.\" @(#)mmap.2 8.4 (Berkeley) 5/11/95
+.\" $FreeBSD: src/lib/libc/sys/mmap.2,v 1.56 2007/01/09 00:28:15 imp Exp $
.\"
-.Dd June 4, 1993
+.Dd April 21, 2006
.Dt MMAP 2
-.Os BSD 4
+.Os
.Sh NAME
.Nm mmap
-.Nd map files or devices into memory
+.Nd allocate memory, or map files or devices into memory
+.Sh LIBRARY
+.Lb libc
.Sh SYNOPSIS
-.Fd #include <sys/types.h>
-.Fd #include <sys/mman.h>
+.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
+.Fn mmap
+system call causes the pages starting at
.Fa addr
and continuing for at most
.Fa len
.Fa len
is not a multiple of the pagesize, the mapped region may extend past the
specified range.
+Any extension beyond the end of the mapped object will be zero-filled.
.Pp
-If
+The
.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.)
+argument is used by the system to determine the starting address of the mapping,
+and its interpretation is dependent on the setting of the MAP_FIXED flag.
+If MAP_FIXED is specified in
+.Fa flags ,
+the system will try to place the mapping at the specified address,
+possibly removing a
+mapping that already exists at that location.
+If MAP_FIXED is not specified,
+then the system will attempt to use the range of addresses starting at
+.Fa addr
+if they do not overlap any existing mappings,
+including memory allocated by malloc(3) and other such allocators.
+Otherwise,
+the system will choose an alternate address for the mapping (using an implementation
+dependent algorithm)
+that does not overlap any existing
+mappings.
+In other words,
+without MAP_FIXED the system will attempt to find an empty location in the address space if the specified address
+range has already been mapped by something else.
If
.Fa addr
-is zero, an address will be selected by the system.
-The actual starting address of the region is returned.
-A successful
+is zero and MAP_FIXED is not specified,
+then an address will be selected by the system so as not to overlap
+any existing mappings in the address space.
+In all cases,
+the actual starting address of the region is returned.
+If MAP_FIXED is specified,
+a successful
.Fa mmap
deletes any previous mapping in the allocated address range.
+Previous mappings are never deleted if MAP_FIXED is not specified.
.Pp
The protections (region accessibility) are specified in the
.Fa prot
.Em or Ns 'ing
the following values:
.Pp
-.Bl -tag -width MAP_FIXEDX
-.It Dv PROT_EXEC
-Pages may be executed.
+.Bl -tag -width PROT_WRITE -compact
+.It Dv PROT_NONE
+Pages may not be accessed.
.It Dv PROT_READ
Pages may be read.
.It Dv PROT_WRITE
Pages may be written.
+.It Dv PROT_EXEC
+Pages may be executed.
.El
.Pp
+Note that, due to hardware limitations, on some platforms PROT_WRITE may
+imply PROT_READ, and PROT_READ may imply PROT_EXEC. Portable programs
+should not rely on these flags being separately enforcable.
+.Pp
The
.Fa flags
-parameter specifies the type of the mapped object, mapping options and
+argument 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.
+to the process (copy-on-write) or are to be shared with other references.
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_FIXEDX
+.Bl -tag -width MAP_HASSEMAPHORE
+.It Dv MAP_ANONYMOUS
+Synonym for
+.Dv MAP_ANON.
.It Dv MAP_ANON
Map anonymous memory not associated with any specific file.
-The file descriptor used for creating
+The
+.Fa offset
+argument is ignored.
+Mac OS X specific: the file descriptor used for creating
.Dv MAP_ANON
-regions is used only for
-naming, and may be specified as \-1 if no name is associated with the
-region.
+regions can be used to pass some Mach VM flags, and can
+be specified as \-1 if no such flags are associated with
+the region. Mach VM flags are defined in
+<mach/vm_statistics.h> and the ones that currently apply
+to
+.Nm mmap
+are:
+.Pp
+VM_FLAGS_PURGABLE to create Mach purgable (i.e. volatile) memory.
+.Pp
+VM_MAKE_TAG(tag) to associate an 8-bit tag with the region.
+.br
+<mach/vm_statistics.h> defines some preset tags (with a VM_MEMORY_ prefix).
+Users are encouraged to use tags between 240 and 255.
+Tags are used by tools such as vmmap(1) to help identify specific memory regions.
+.Pp
.It Dv MAP_FILE
-Mapped from a regular file or character-special device memory. (This is
+Mapped from a regular file. (This is
the default mapping type, and need not be specified.)
.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
+.Fn mmap
will fail.
-If MAP_FIXED is specified,
+If
+.Dv MAP_FIXED
+is specified,
.Fa addr
must be a multiple of the pagesize.
+If a
+.Dv MAP_FIXED
+request is successful, the mapping established by
+.Fn mmap
+replaces any previous mappings for the process' pages in the range from
+.Fa addr
+to
+.Fa addr
++
+.Fa len .
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_PRIVATE
-Modifications are private.
+Modifications are private (copy-on-write).
.It Dv MAP_SHARED
Modifications are shared.
+.It Dv MAP_NOCACHE
+Pages in this mapping are not retained in the kernel's memory cache.
+If the system runs low on memory, pages in MAP_NOCACHE mappings will be among
+the first to be reclaimed.
+This flag is intended for mappings that have little locality and
+provides a hint to the kernel that pages in this mapping are unlikely to be needed
+again in the near future.
.El
.Pp
-The
+Conforming applications must specify either MAP_PRIVATE or MAP_SHARED.
+.Pp
+The
.Xr close 2
-function does not unmap pages, see
+system call does not unmap pages, see
.Xr munmap 2
for further information.
.Pp
should be done.
.Sh RETURN VALUES
Upon successful completion,
-.Nm mmap
+.Fn mmap
returns a pointer to the mapped region.
-Otherwise, a value of -1 is returned and
+Otherwise, a value of
+.Dv MAP_FAILED
+is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
-.Fn Mmap
+The
+.Fn mmap
+system call
will fail if:
.Bl -tag -width Er
.It Bq Er EACCES
.Dv PROT_READ
was specified as part of the
.Fa prot
-parameter and
+argument and
.Fa fd
was not open for reading.
The flags
-.Dv PROT_WRITE
-and
.Dv MAP_SHARED
-were specified as part
-of the
+and
+.Dv PROT_WRITE
+were specified as part of the
.Fa flags
and
.Fa prot
-parameters and
+argument and
.Fa fd
was not open for writing.
.It Bq Er EBADF
+The
.Fa fd
+argument
is not a valid open file descriptor.
.It Bq Er EINVAL
.Dv MAP_FIXED
was specified and the
-.I addr
-parameter was not page aligned.
+.Fa addr
+argument was not page aligned, or part of the desired address space
+resides out of the valid address space for a user process.
+.It Bq Er EINVAL
+.Fa flags
+does not include either MAP_PRIVATE or MAP_SHARED.
+.It Bq Er EINVAL
+The
+.Fa len
+argument
+was negative or zero. Historically, the system call would not return an error if the argument was zero.
+See other potential additional restrictions in the
+COMPATIBILITY section below.
+.It Bq Er EINVAL
+The
+.Fa offset
+argument
+was not page-aligned based on the page size as returned by getpagesize(3).
+.It Bq Er ENODEV
+.Dv MAP_ANON
+has not been specified and the file
.Fa fd
-did not reference a regular or character special file.
+refers to does not support mapping.
.It Bq Er ENOMEM
.Dv MAP_FIXED
was specified and the
.Fa addr
-parameter wasn't available.
+argument was not available.
+.Dv MAP_FIXED
+was specified and the address range specified exceeds the address space
+limit for the process.
.Dv MAP_ANON
was specified and insufficient memory was available.
+.It Bq Er ENXIO
+Addresses in the specified range are invalid for
+.Fa fd .
+.It Bq Er EOVERFLOW
+Addresses in the specified range exceed the maximum offset
+set for
+.Fa fd .
.El
-.Sh "SEE ALSO"
-.Xr getpagesize 2 ,
-.Xr msync 2 ,
-.Xr munmap 2 ,
-.Xr mprotect 2 ,
+.Sh LEGACY SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <sys/mman.h>
+.Pp
+The include file
+.In sys/types.h
+is necessary.
+.Sh COMPATIBILITY
+.Fn mmap
+now returns with
+.Va errno
+set to EINVAL in places that historically succeeded.
+The rules have changed as follows:
+.Bl -bullet
+.It
+The
+.Fa flags
+parameter must specify either MAP_PRIVATE or MAP_SHARED.
+.It
+The
+.Fa len
+parameter must not be 0.
+.It
+The
+.Fa off
+parameter must be a multiple of pagesize,
+as returned by
+.Fn sysconf .
+.El
+.Sh SEE ALSO
.Xr madvise 2 ,
.Xr mincore 2 ,
-.Xr mlock 2
+.Xr minherit 2 ,
+.Xr mlock 2 ,
+.Xr mprotect 2 ,
+.Xr msync 2 ,
+.Xr munlock 2 ,
+.Xr munmap 2 ,
+.Xr shmat 2 ,
+.Xr getpagesize 3
projects / apple / xnu.git / blobdiff