[vlc-devel] [PATCH] v4l/v4l2: add mmap() fall back for nommu systems

Rémi Denis-Courmont rem at videolan.org
Thu Mar 12 14:00:02 CET 2009

Le mercredi 11 mars 2009 19:36:38 Mike Frysinger, vous avez écrit :
> >> I'm not really sure how MAP_PRIVATE works. According to the man page it
> >> creates a private copy on write mapping. Won't that mean that the
> >> original memory area doesn't get updated?
> >
> > Yes. That's the whole point of MAP_PRIVATE - doing copy-on-write to not
> > share your modifications with others.
> which is why i made it a fallback.  attempting to use MAP_SHARED on a
> nommu system results in a failure.  generally nommu does not have
> multiple programs running simultaneously because it's an embedded
> system, not a desktop, so only having one application run
> simultaneously is the norm.

I guess Antoine meant to ask how it works at all in case of v4l(2). In other 
words, how can the kernel driver update the content of memory if we use 
MAP_PRIVATE? (Note that I don't know V4L myself at all)

Rémi Denis-Courmont

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