linux-kernel - Re: [PATCH 2/6] nfsd: swap fs root in NFSd kthreads

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Message-ID: <20121211145443.GH4939@ZenIV.linux.org.uk>
Date:	Tue, 11 Dec 2012 14:54:43 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	devel@...nvz.org
Subject: Re: [PATCH 2/6] nfsd: swap fs root in NFSd kthreads

On Tue, Dec 11, 2012 at 06:00:00PM +0400, Stanislav Kinsbursky wrote:
> 11.12.2012 00:28, J. Bruce Fields ??????????:
> >On Thu, Dec 06, 2012 at 06:34:47PM +0300, Stanislav Kinsbursky wrote:
> >>NFSd does lookup. Lookup is done starting from current->fs->root.
> >>NFSd is a kthread, cloned by kthreadd, and thus have global (but luckely
> >>unshared) root.
> >>So we have to swap root to those, which process, started NFSd, has. Because
> >>that process can be in a container with it's own root.
> >
> >This doesn't sound right to me.
> >
> >Which lookups exactly do you see being done relative to
> >current->fs->root ?
> >
> 
> Ok, you are right. I was mistaken here.
> This is not a exactly lookup, but d_path() problem in svc_export_request().
> I.e. without root swapping, d_path() will give not local export path (like "/export")
> but something like this "/root/containers_root/export".

Now, *that* is a different story (and makes some sense).  Take a look
at __d_path(), please.  You don't need to set ->fs->root to get d_path()
equivalent relative to given point.
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