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SubjectRe: The INN/mmap bug
Alexander Viro wrote:
> On Mon, 18 Sep 2000, Andreas Dilger wrote:
> > Alexander writes:
> > > * uptodate pages should never become non-uptodate.
> > > uptodate .. pages ... never have data _older_ than on disk
> >
> > This may actually be a problem in the future... what about shared access
> > block devices like FCAL or a distributed filesystem? It has to be
> > possible for pages to become non-uptodate in a sane way.
> So what the heck do you do when something modifies mmaped page when you
> get the change of on-disk one? Say it, writer is notified that write had
> been completed, sends packet to you and you flip a bit on a page that
> happens to be mmaped on the place where write had happened.
> Write-through-pagecache is OK, but write straight to disk bypassing the
> cache? Welcome to the fun with aliases...

Yes, I think that's one rule we can write down right now: to update a
block on disk you have to go through the buffer. Not going through
the buffer is about the same as accessing a semaphore-protected
resource without bothering with the semaphore.

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