linux-kernel - Re: sysfs: tagged directories not merged completely yet

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Date:	Wed, 08 Oct 2008 08:17:31 +0900
From:	Tejun Heo <tj@...nel.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Al Viro <viro@...IV.linux.org.uk>,
	Benjamin Thery <benjamin.thery@...l.net>,
	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Al Viro <viro@....linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: sysfs: tagged directories not merged completely yet

Hello, a bit of additions after some sleep.

Tejun Heo wrote:
> Eric W. Biederman wrote:
> IIRC, the original readdir implementation put a cursor entry to walk
> through the children list.  The implementation was horribly broken in
> a number of different ways (ISTR problems with locking and multiple
> and different type of walkers) and I just gutted out all the
> complexity out and made it simple as getting it correct was far more
> important and there seemed to be little need for optimization.
> 
> Yeah, using RCU sounds like a plan.

Heh... it did sound like a plan but I don't think the plan would solve
the problem.  filldir can't be put in rcu read critical section.  :-p

>> The revalidate on access model doesn't appear to have a way to track
>> remote renames.  Something sysfs supports.
> 
> Yeap, IIRC, one of the reasons why sysfs wasn't converted over to
> sysfs was because sysfs guarantees inode doesn't change over rename or
> move so that notifications keep working over renames.

s/over to sysfs/over to revalidation/ and s/inode/dentry/.  Maybe we can
just ignore dnotify?  :-(

Thanks.

-- 
tejun
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