Linux man pages : msync (2)
MSYNC(2) Linux Programmer's Manual MSYNC(2)
msync - synchronize a file with a memory map
int msync(const void *start, size_t length, int flags);
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 corre-
sponds 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 speci-
fies 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).
On success, zero is returned. On error, -1 is returned, and errno is
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.
POSIX.1b (formerly POSIX.4)
mmap(2), B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.
Linux 1.3.86 1996-04-12 MSYNC(2)