linux-kernel - Re: [PATCH 0/5] fuse: close file synchronously

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Message-ID: <CAJfpegtvfunCV4cjezQuWji3PoJRpXXKWgH+y55tYMi0O+TdkQ@mail.gmail.com>
Date:	Mon, 15 Apr 2013 17:30:41 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Maxim Patlasov <mpatlasov@...allels.com>
Cc:	dev@...allels.com, xemul@...allels.com,
	fuse-devel@...ts.sourceforge.net, bfoster@...hat.com,
	linux-kernel@...r.kernel.org, devel@...nvz.org,
	anand.avati@...il.com
Subject: Re: [PATCH 0/5] fuse: close file synchronously

On Mon, Apr 15, 2013 at 5:08 PM, Miklos Szeredi <miklos@...redi.hu> wrote:
> For example doing a readlink() on a magic symlink under /proc
> shouldn't result in a synchronous call to a fuse filesystem.  Making
> fput() synchronous may actually end up doing that (even if it's not
> very likely).

Thinking about this a bit more.  As it is it sounds wrong to rely on a
synchronous release, when in fact release is just not synchronous, as
indicated by the above example.  Maybe it's the proc code that's buggy
and shouldn't do get_file/fput because everyone is assuming release
being synchronous with close().  Don't know.

Let's approach it from the other direction:  what if you give back the
write lease on the first flush?  It will probably work fine for 99% of
cases, since no other writes are going to happen after the first
flush.  For the remaining cases you'll just have to reacquire the
lease when a write happens after the flush.  I guess performance-wise
that will not be an issue, but I may be wrong.

Thanks,
Miklos
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