netdev - Re: [PATCH 12/15] driver core: Implement tagged directory support for device classes.

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Message-ID: <m11w1u9w5j.fsf@frodo.ebiederm.org>
Date:	Tue, 15 Jul 2008 23:32:24 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Tejun Heo <htejun@...il.com>
Cc:	Greg KH <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	linux-kernel@...r.kernel.org, Al Viro <viro@....linux.org.uk>,
	Linux Containers <containers@...ts.osdl.org>,
	Benjamin Thery <benjamin.thery@...l.net>,
	netdev@...r.kernel.org
Subject: Re: [PATCH 12/15] driver core: Implement tagged directory support for device classes.

Tejun Heo <htejun@...il.com> writes:

> It's a bit scary tho.  Working inode->i_dentry or dentry->d_alias
> crosses multiple sb's.  sysfs isn't too greedy about dcache/icache.
> Only open files and directories hold them and only single copy of
> sysfs_dirent is there for most nodes.  Wouldn't it be better to stay on
> the safer side and use separate inode hierarchy?

To do that I believe we would need to ensure sysfs does not use 
the inode->i_mutex lock except to keep the VFS layer out.  Allowing us
to safely change the directory structure, without holding it.

You raise a good point about inode->i_dentry and dentry->d_alias.
Generally they are used by fat like filesystems but I am starting to
see uses in generic pieces of code.  I don't see any problems today
but yes it would be good to do the refactoring to allow us to duplicate
the inodes. 

Eric

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