HP-UX Reference (11i v1 00/12) - 2 System Calls (vol 5)
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STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man2/!!!intro.2
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m
msync(2) msync(2)
NAME
msync - synchronize memory with physical storage
SYNOPSIS
#include <sys/mman.h>
int msync(void *addr,size_t len, int flags);
DESCRIPTION
The msync() function writes all modified copies of pages over the range [addr, addr+len] to the underly-
ing hardware, or invalidates any copies so that further references to the pages will be obtained by the sys-
tem from their permanent storage locations.
The flags argument is one of the following:
MS_ASYNC perform asynchronous writes
MS_SYNC perform synchronous writes
MS_INVALIDATE invalidate mappings
If flags is MS_ASYNC or MS_SYNC, the function synchronizes the file contents to match the current con-
tents of the memory region.
• All write references to the memory region made prior to the call are visible by subsequent read
operations on the file.
• It is unspecified whether writes to the same portion of the file prior to the call are visible by read
references to the memory region.
• It is unspecified whether unmodified pages in the specified range are also written to the underlying
hardware.
If flags is
MS_ASYNC, the function may return immediately once all write operations are scheduled; if flags
is
MS_SYNC, the function does not return until all write operations are completed.
If flags is MS_INVALIDATE
, the function synchronizes the contents of the memory region to match the
current file contents.
• All writes to the mapped portion of the file made prior to the call are visible by subsequent read
references to the mapped memory region.
• It is unspecified whether write references prior to the call, by any process, to memory regions
mapped to the same portion of the file using
MAP_SHARED, are visible by read references to the
region.
If msync() causes any write to the file, then the file’s st_ctime and st_mtime fields are marked for update.
RETURN VALUE
Upon successful completion,
msync() returns 0. Otherwise, it returns −1 and sets errno to indicate the
error.
ERRORS
The msync() function will fail if:
[EINVAL] The addr argument is not a multiple of the page size as returned by sys-
conf()
.
[EIO] An I/O error occurred while reading from or writing to the file system.
[ENOMEM] Some or all the addresses in the range [addr, addr+len] are invalid for the
address space of the process or pages not mapped are specified.
APPLICATION USAGE
The msync() function should be used by programs that require a memory object to be in a known state,
for example in building transaction facilities.
Normal system activity can cause pages to be written to disk. Therefore, there are no guarantees that
msync() is the only control over when pages are or are not written to disk.
HP-UX Release 11i: December 2000 − 1 − Section 2−−191
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