Messages in this thread | | | Date | Fri, 19 Nov 2004 08:56:16 -0800 | From | Matt Mackall <> | Subject | Re: [PATCH 17/20] FRV: Better mmap support in uClinux |
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On Fri, Nov 19, 2004 at 04:26:43PM +0000, David Howells wrote: > > > > (3) Files (and blockdevs) cannot be mapped shared since it is not > > > really possible to honour this by writing any changes back to the > > > backing device. > > > > [way behind on email] > > > > I think this could be done at msync, munmap and exit time? You end up > > flushing the entire mapping, but it's still correct (and POSIX > > compliant). > > Don't forget write() too. If someone does a write, that would have to be > written over the mapping too. Obviously this is not impossible.
I don't see such a requirement, but it'd be nice, yes. > > And, if you wanted to be really clever, you could store a hash of each > > page to detect changes and avoid the extra I/O. > > It'd probably have to be something like an md5 sum.
Arguably, it needn't be cryptographically strong. But that's another discussion.
> Okay, technically, we could probably emulate it, but is it worth it? I think > it's something to bear in mind for another time.
Well I wasn't volunteering, just pointing out it's not as hard as claimed. Thankfully all the boxes I currently have to care about are not so special.
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