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

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Message-ID: <487D8C0A.9060100@gmail.com>
Date:	Wed, 16 Jul 2008 14:50:02 +0900
From:	Tejun Heo <htejun@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.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.

Hello,

Eric W. Biederman wrote:
>> Eric, with the multiple superblocks, sysfs now uses inode from the
>> default sysfs_sb with dentries from other sb's.  Is this okay?  Are
>> there any other filesystems which do this?
> 
> I don't know of any other filesystems where this unique challenge arises.
> /proc almost qualifies but it never needs to be modified.
> 
> It is certainly ok to go from multiple dentries to a single inode.
> I'm trying to remember why I choose to do that.  I think both because it simplifies
> the locking and keeps us more efficient in the icache.

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?

Thanks.

-- 
tejun
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