linux-kernel - Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

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Date:	Fri, 26 Oct 2012 13:52:54 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	"Myklebust, Trond" <Trond.Myklebust@...app.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [PATCH v3] SUNRPC: set desired file system root before
 connecting local transports

On Wed, Oct 10, 2012 at 02:32:28PM +0400, Stanislav Kinsbursky wrote:
> 10.10.2012 05:23, J. Bruce Fields пишет:
> >On Tue, Oct 09, 2012 at 03:47:42PM -0700, Eric W. Biederman wrote:
> >>"J. Bruce Fields" <bfields@...ldses.org> writes:
> >>
> >>>On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
> >>>>"Myklebust, Trond" <Trond.Myklebust@...app.com> writes:
> >>>>
> >>>>>On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
> >>>>>>Cc'ing Eric since I seem to recall he suggested doing it this way?
> >>>>
> >>>>Yes.  On second look setting fs->root won't work. We need to change fs.
> >>>>The problem is that by default all kernel threads share fs so changing
> >>>>fs->root will have non-local consequences.
> >>>
> >>>Oh, huh.  And we can't "unshare" it somehow?
> >>
> >>I don't fully understand how nfs uses kernel threads and work queues.
> >>My general understanding is work queues reuse their kernel threads
> >>between different users.  So it is mostly a don't pollute your
> >>environment thing.  If there was a dedicated kernel thread for each
> >>environment this would be trivial.
> >>
> >>What I was suggesting here is changing task->fs instead of
> >>task->fs.root.  That should just require task_lock().
> >
> >Oh, OK, got it--if that works, great.
> >
> 
> The main problem with swapping fs struct is actually the same as in
> root swapping. I.e. routines for copy fs_struct are not exported.
> It could be done on place, but I don't think, that Al Viro would
> support such implementation.
> Trond?

It seems like we got stalled here....  Could you go ahead and try a
patch, and see what people think?

--b.
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