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NetBSD 6.1.5 - man page for mmap (netbsd section 2)

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MMAP(2) 			     BSD System Calls Manual				  MMAP(2)

NAME
     mmap -- map files or devices into memory

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/mman.h>

     void *
     mmap(void *addr, size_t len, int prot, int flags, int fd, off_t offset);

DESCRIPTION
     The mmap function causes the pages starting at 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 fol-
     lowing values:

	   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.

     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 or MAP_PRIVATE must be specified.
     Sharing, mapping type and options are specified in the flags argument by OR'ing the follow-
     ing values:

	   MAP_ALIGNED(n)      Request that the allocation be aligned to the given boundary.  The
			       parameter n should be the base 2 logarithm of the desired align-
			       ment (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 sysconf(3) with the _SC_PAGESIZE request.

	   MAP_ANON	       Map anonymous memory not associated with any specific file.  The
			       file descriptor is not used for creating MAP_ANON regions, and
			       must be specified as -1.  The mapped memory will be zero filled.

	   MAP_FILE	       Mapped from a regular file or character-special device memory.

	   MAP_FIXED	       Do not permit the system to select a different address than the
			       one specified.  If the specified address cannot be used, mmap will
			       fail.  If MAP_FIXED is specified, addr must be a multiple of the
			       pagesize.  Use of this option is discouraged.

	   MAP_HASSEMAPHORE    Notify the kernel that the region may contain semaphores and that
			       special handling may be necessary.

	   MAP_INHERIT	       Permit regions to be inherited across execve(2) system calls.

	   MAP_TRYFIXED        Attempt to use the address addr even if it falls within the nor-
			       mally 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	       Lock the mapped region into memory as with mlock(2).

	   MAP_PRIVATE	       Modifications made by this process are private, however modifica-
			       tions made by other processes using MAP_SHARED will be seen.

	   MAP_SHARED	       Modifications are shared.

     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.

RETURN VALUES
     Upon successful completion, mmap returns a pointer to the mapped region.  Otherwise, a value
     of MAP_FAILED is returned and errno is set to indicate the error.	The symbol MAP_FAILED is
     defined in the header <sys/mman.h>.  No successful return from mmap() will return the value
     MAP_FAILED.

ERRORS
     mmap() will fail if:

     [EACCES]		The flag 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.

SEE ALSO
     madvise(2), mincore(2), mlock(2), mprotect(2), msync(2), munmap(2), getpagesize(3),
     sysconf(3)

STANDARDS
     The mmap() function conforms to IEEE Std 1003.1b-1993 (``POSIX.1'').

HISTORY
     The mmap() interface was first designed in 4.2BSD.

BSD					December 20, 2011				      BSD
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