linux-kernel - Re: [RFC] FUSE: mnotify (was: [RFC] VFS: mnotify)

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Date:	Sun, 12 Aug 2007 13:24:37 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Al Boldi <a1426z@...ab.com>
cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] FUSE: mnotify (was: [RFC] VFS: mnotify)


On Aug 12 2007 06:32, Al Boldi wrote:
>Al Boldi wrote:
>> Jakob Oestergaard wrote:
>> > Why on earth would you cripple the kernel defaults for ext3 (which is a
>> > fine FS for boot/root filesystems), when the *fundamental* problem you
>> > really want to solve lie much deeper in the implementation of the
>> > filesystem?  Noatime doesn't solve the problem, it just makes it "less
>> > horrible".
>>
>> inotify could easily solve the atime problem, but it's got the drawback of
>> forcing the user to register each and every file/dir of interest, which
>> isn't really reasonable on TB-filesystems.

What inotify needs is some kind of SUBDIR flag on a watch so that one does not
run out of fds, then the TB issue becomes a bit lighter I think.

>> It could be feasible to introduce mnotify, which would notify the user of
>> meta changes, like atime, across the filesystem.  Something like mnotify
>> could also be helpful in CoW situations, provided it supported an in-sync
>> interface.
>
>Here is an idea:  Could FUSE be used to produce mnotify behaviour?

It may, and in some cases, not. For example, I only had a single filesystem,
and would like atime notificatios for it, then how would I do that? What comes
to mind is to use a fuse fs that mirrors, but also notifies, ergo:
	mount -t fuse.lomount / /mnt
Well, wonderful, now I still need to pivot_root to /mnt, so that all accesses
actually end up in fuse-land. And this gets ugly on shutdown, when things have
to be unmounted.


	Jan
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