linux-kernel - Re: [fuse-devel] [PATCH 01/25] VFS: move attr_kill logic from notify

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Message-Id: <E1IILwa-0007Eq-00@dorka.pomaz.szeredi.hu>
Date:	Tue, 07 Aug 2007 12:05:40 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	trond.myklebust@....uio.no
CC:	miklos@...redi.hu, jlayton@...hat.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	mikulas@...ax.karlin.mff.cuni.cz, zippel@...ux-m68k.org,
	joel.becker@...cle.com, wli@...omorphy.com, dhowells@...hat.com,
	bfennema@...con.csc.calpoly.edu
Subject: Re: [fuse-devel] [PATCH 01/25] VFS: move attr_kill logic from
	notify_change into helper function

There's another way to deal with this in NFS and fuse, without having
to change the API:

 - remove suid/sgid bits from i_mode, when refreshing the inode attributes
 - store the removed bits (or the original mode)  in the fs' inode strucure
 - in ->getattr() restore the original mode into the returned stat

This way the VFS believes, that the inode does not in fact have the
suid/sgid bits and so won't call ->setattr() unnecessarily.

I've tested a similar change in fuse for working around unneeded check
for the directory sticky bit.

Yes, this is cheating the interface, but there's a deeper level where
it makes sense: the VFS should not be checking _any_ inode attribute
besides the file type, since they can change at any moment, and the
VFS might be using stale data without having first properly
revalidated it.

Miklos
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