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SubjectRe: [fuse-devel] [PATCH] FUSE/CUSE: implement direct mmap support
On Wed, 10 Feb 2010, Tejun Heo wrote:
> > Okay, lets be a little clearer. There are client side maps and server
> > side maps. Client side maps are naturally aligned (same offset ->
> > same page).
> Same offset -> same page doesn't hold.

Right, I really meant same page -> same offset. If the same offset is
mapped to multiple pages: no problem. If the same page is mapped to
multiple offsets, then obviously it's not going to work properly.

> Can you please elaborate how you think the thing can work without
> referencing the proposed implementation? Let's find out where the
> misundertanding is.

Thinking about it I'm not really sure...

Maybe the problem is that the propsed solution allows too much
freedom. Normally there's a 1:1 relationship between pages and
offsets. But we want to break that for CUSE, because two different
mappings of a char dev might point to completely different pages,

When does that happen? Can it happen that two mappings of the same
file descriptor will have different backing pages?


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