void
*
mmap(
void *addr
, size_t len
, int prot
, int flags
, int fd
, off_t offset
)
addr
and continuing for at most
len
bytes to be mapped from the object described by
fd
,
starting at byte offset
offset
.
If
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.
If
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
addr
is zero, an address will be selected by the system.
The actual starting address of the region is returned.
A successful
mmap
deletes any previous mapping in the allocated address range.
The protections (region accessibility) are specified in the
prot
argument by
OR'ing
the following values:
PROT_EXEC
PROT_READ
PROT_WRITE
PROT_NONE
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
enforceable.
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.
Note that either
MAP_SHARED
,
MAP_PRIVATE
or
MAP_COPY
must be specified.
Sharing, mapping type and options are specified in the
flags
argument by
OR'ing
the following values:
MAP_ALIGNED(n)
_SC_PAGESIZE
request.
MAP_ANON
MAP_ANON
regions, and must be specified as -1.
The mapped memory will be zero filled.
MAP_FILE
MAP_FIXED
addr
must be a multiple of the pagesize.
Use of this option is discouraged.
MAP_HASSEMAPHORE
MAP_INHERIT
MAP_TRYFIXED
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
addr
is
NULL
,
this flag is ignored and the system will select a mapping address.
MAP_WIRED
MAP_PRIVATE
MAP_SHARED
will be seen.
MAP_SHARED
MAP_COPY
The close(2) function does not unmap pages, see munmap(2) for further information.
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,
MAP_SWAP
,
in which
the file descriptor argument specifies a file or device to which swapping
should be done.
If
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.
MAP_FAILED
is returned and
errno
is set to indicate the error.
The symbol
MAP_FAILED
is defined in the header
sys/mman.h<.blm Pp
. >
No successful return from
mmap(
)
will return the value
MAP_FAILED
.
)
will fail if:
EACCES
]
PROT_READ
was specified as part of the
prot
parameter and
fd
was not open for reading.
The flags
MAP_SHARED
and
PROT_WRITE
were specified as part of the
flags
and
prot
parameters and
fd
was not open for writing.
EBADF
]
fd
is not a valid open file descriptor.
EINVAL
]
MAP_FIXED
was specified and the
addr
parameter was not page aligned or was outside of the
valid address range for a process.
MAP_ANON
was
specified
and
fd
was not -1.
ENODEV
]
fd
did not reference a regular or character special file.
ENOMEM
]
MAP_FIXED
was specified and the
addr
parameter wasn't available.
MAP_ANON
was specified and insufficient memory was available.
EOVERFLOW
]
fd
references a regular file and the value of
offset
plus
len
would exceed the offset maximum established in its open file description.
MAP_COPY
flag is not implemented.
The current
MAP_COPY
semantics are the same as those of the
MAP_PRIVATE
flag.