Date: Tue, 10 Jun 2008 17:50:24 -0500
From: "Serge E. Hallyn" <serue@us.ibm.com>
To: Benjamin Thery <benjamin.thery@bull.net>
Cc: Greg Kroah-Hartman <gregkh@suse.de>,
       Andrew Morton <akpm@linux-foundation.org>,
       Eric Biederman <ebiederm@xmission.com>, Serge Hallyn <serue@us.ibm.com>,
       linux-kernel@vger.kernel.org, Tejun Heo <htejun@gmail.com>,
       Al Viro <viro@ftp.linux.org.uk>,
       Linux Containers <containers@lists.osdl.org>
Subject: Re: [PATCH 00/11] sysfs tagged directories V5
Message-ID: <20080610225024.GB22478@us.ibm.com>
References: <20080606154654.356185262@theryb.frec.bull.fr>
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Quoting Benjamin Thery (benjamin.thery@bull.net):
> Greg,
> 
> Here is an updated version of the sysfs tagged directories that improves
> a bit the situation over the previous one. 
> 
> I've modified the patch 09 ("Enable tagging for net_class directories in 
> sysfs") to be a bit less intrusive in sysfs core. I removed the #ifdef'd
> parts you didn't like in fs/sysfs/mount.c, and replaced it by a generic 
> routine sysfs_ns_exit() that is called, if needed, by the namespace when
> it exits. This routine goes through every sysfs super blocks and calls 
> the callback passed by the namespace to clean its tag.
> 
> The patch is now splitted in two: 
> * 09/11: the generic routine,
> * 10/11: the remaining network parts.
> 
> The generic part can be merge with patch 05 ("sysfs: Implement sysfs 
> tagged directory support.") but I left it separate for now to ease 
> reviews.

Thanks.  Not nearly as radical as I'd feared.

Greg, does this address your concern?  It stops the need to put any
non-braindead code (i.e. the _exit notifier stuff) in fs/sysfs/mount.c for
any new namespaces needing sysfs tagging, leaving only simple
comparison/assignments.

> Serge's patch for user namespace is modified to use this new service too.
> No more #ifdef CONFIG_NET or #ifdef CONFIG_USER_NS in fs/sysfs/mount.c 
> now.
> 
> 
> But, currently, a new namespace that wants to add its tag to sysfs dirs
> still need to modify fs/sysfs/mount.c in a few routines to manage the
> new tag member added in struct sysfs_tag_info: sysfs_fill_super(), 
> sysfs_test_super(), sysfs_kill_sb() (see the last two patches).
> These changes are only the initialization and a bunch of comparisons.
> 
> If we really want to go further, to get rid of these, I've thought 
> about:
> 
> * Extending sysfs_tagged_dir_operations with super blocks operations: 
>   - fill_sb_tag, test_sb_tag, kill_sb_tag
> 
> * Add routines in sysfs to allow registration/unregistration of these 
>   operations structs in a list:
>   - sysfs_register_tagged_dir_ops()...
> 
> * Each subsystem concerned implements and registers its operations at 
>   boot.
>
> * In sysfs_fill_super(), sysfs_test_super() and sysfs_kill_sb(), add 
>   loops to go through all registered operations structs and calls the 
>   corresponding operations if it's present.
> 
> But... I thought it was a bit overkill for the few namespaces that will 
> actually need sysfs tagged directories.

Agreed.  We expect device namespaces...  anything else?

thanks,
-serge
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