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SubjectRe: how mmap() works?

On 03.30 Jerry Hong wrote:
> Hi,
> mmap() creates a mmaped memory associated with a
> physical file. If a process updates the mmaped memory,
> Linux will updates the file "automatically". If this
> is the case, why do we need msync()? If this is not

Where did you heard that ?

man mmap(2):
..
MAP_SHARED Share this mapping with all other processes
that map this object. Storing to the region is
equivalent to writing to the file. The file
may not actually be updated until msync(2) or
munmap(2) are called.
..
man msync(2):
..
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
.

--
J.A. Magallon # Let the source
mailto:jamagallon@able.es # be with you, Luke...

Linux werewolf 2.4.2-ac28 #1 SMP Thu Mar 29 16:41:17 CEST 2001 i686

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