linux-kernel - Re: [patch 04/14] gfs2: dont call permission()

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Date:	Fri, 23 May 2008 13:01:10 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	swhiteho@...hat.com
CC:	miklos@...redi.hu, hch@...radead.org,
	linux-fsdevel@...r.kernel.org, viro@...IV.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 04/14] gfs2: dont call permission()

> Given the fact that (a) its only a very minor change and (b) as soon as
> we have a solution to what we really want to do:
> 
>  - inode/file operation:
>    - Do lookup via VFS
>    - Get GFS2 glock
>      - Do perm check via VFS
>      - Do actual operation
>    - Drop GFS2 glock

Well, fuse/nfs already do something similar, except they have their
actual permission checking in the server, as opposed to the vfs.  They
basically do:

 ->permission() does nothing

 ->foo_operation() does everything, including permission checking

The reality is a bit more complicated, and both nfs and fuse do
sometimes check permissions in ->permission() but most of the cases,
when they know that the permission will be checked later anyway they
just omit it.

Of course this would mean, that for example the LSM security checks
are not done within the gfs locked region.  Does that matter?

Miklos
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