Re: [PATCH] loop.c to use write ops for fs requiring special locking

[Christoph Hellwig <hch@infradead.org>]

You still don't get it.

Calling address space operations directly from generic code is a layering
violation.  This got added during late 2.3/2.4 series to get loop working
again at all.  It's a pretty bad design in general.  We fixed the read side
by adding ->sendfile, and something similar is still needed on the write
side.  We got along with the broken write side because it kinda worked.

It doesn't work for your out of tree filesystem which isn't a problem per
se.  If you want it fixed the only way to get there is to fix it for real
instead of adding another unmaintainable cludge.  So either go ahead and
add a new file operation that is the counterpart to ->sendfile or go away.

And please take a look at Jens Axboe's splice patch, I suspect you could
easily piggyback on that.