MSYNC

Section: Linux Programmer's Manual (2)
Updated: 1996-04-12
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NAME

msync - synchronize a file with a memory map

SYNOPSIS

#include <unistd.h>
#include <sys/mman.h>

#ifdef _POSIX_MAPPED_FILES
#ifdef _POSIX_SYNCHRONIZED_IO

int msync(const void *start, size_t length, int flags);

#endif
#endif

DESCRIPTION

msync flushes changes made to the in-core copy of a file that was mapped into memory using mmap(2) back to disk. Without use of this call there is no guarantee that changes are written back before munmap(2) is called. To be more precise, the part of the file that corresponds to the memory area starting at start and having length length is updated. The flags argument may have the bits MS_ASYNC, MS_SYNC and MS_INVALIDATE set, but not both MS_ASYNC and MS_SYNC. MS_ASYNC specifies that an update be scheduled, but the call returns immediately. MS_SYNC asks for an update and waits for it to complete. MS_INVALIDATE asks to invalidate other mappings of the same file (so that they can be updated with the fresh values just written).

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EINVAL: start is not a multiple of PAGESIZE, or any bit other than MS_ASYNC | MS_INVALIDATE | MS_SYNC is set in flags.
EFAULT: The indicated memory (or part of it) was not mapped.

CONFORMING TO

POSIX.1b (formerly POSIX.4)

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