man2/msync.2

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  25 .TH MSYNC 2 2003-08-21 "Linux 2.4" "Linux Programmer's Manual"
  26 .SH NAME
  27 msync \- synchronize a file with a memory map
  28 .SH SYNOPSIS
  29 .B #include <sys/mman.h>
  30 .sp
  31 .BI "int msync(void *" start ", size_t " length ", int " flags );
  32 .SH DESCRIPTION
  33 .BR msync ()
  34 flushes changes made to the in-core copy of a file that was mapped
  35 into memory using
  36 .BR mmap (2)
  37 back to disk.  Without use of this call
  38 there is no guarantee that changes are written back before
  39 .BR munmap (2)
  40 is called.  To be more precise, the part of the file that
  41 corresponds to the memory area starting at
  42 .I start
  43 and having length
  44 .I length
  45 is updated.  The
  46 .I flags
  47 argument may have the bits MS_ASYNC, MS_SYNC and MS_INVALIDATE set,
  48 but not both MS_ASYNC and MS_SYNC.
  49 MS_ASYNC specifies that an update be scheduled, but the call
  50 returns immediately.
  51 MS_SYNC asks for an update and waits for it to complete.
  52 MS_INVALIDATE asks to invalidate other mappings of the same file
  53 (so that they can be updated with the fresh values just written).
  54 .SH "RETURN VALUE"
  55 On success, zero is returned.  On error, \-1 is returned, and
  56 .I errno
  57 is set appropriately.
  58 .SH ERRORS
  59 .TP
  60 .BR EINVAL
  61 .I start
  62 is not a multiple of PAGESIZE, or any bit other than
  63 MS_ASYNC | MS_INVALIDATE | MS_SYNC is set in
  64 .IR flags .
  65 .TP
  66 .B ENOMEM
  67 The indicated memory (or part of it) was not mapped.
  68 .SH AVAILABILITY
  69 On POSIX systems on which
  70 .BR msync ()
  71 is available, both
  72 .B _POSIX_MAPPED_FILES
  73 and
  74 .B _POSIX_SYNCHRONIZED_IO
  75 are defined in <unistd.h> to a value greater than 0. (See also
  76 .BR sysconf (3).)
  77 .\" POSIX 1003.1-2001: It shall be defined to -1 or 0 or 200112L.
  78 .\" -1: unavailable, 0: ask using sysconf().
  79 .\" glibc defines them to 1.
  80 .SH "CONFORMING TO"
  81 POSIX.1b (formerly POSIX.4)
  82
  83 This call was introduced in Linux 1.3.21, and then used EFAULT instead of
  84 ENOMEM. In Linux 2.4.19 this was changed to the POSIX value ENOMEM.
  85 .SH "SEE ALSO"
  86 .BR mmap (2)
  87 .br
  88 B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.