linux-kernel - Re: [RFC PATCH 0/5] net: socket bind to file descriptor introduced

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Message-ID: <20120816135429.GF28054@fieldses.org>
Date:	Thu, 16 Aug 2012 09:54:29 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Stanislav Kinsbursky <skinsbursky@...allels.com>,
	tglx@...utronix.de, mingo@...hat.com, davem@...emloft.net,
	hpa@...or.com, thierry.reding@...onic-design.de,
	bfields@...hat.com, eric.dumazet@...il.com, xemul@...allels.com,
	neilb@...e.de, netdev@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, paul.gortmaker@...driver.com,
	viro@...iv.linux.org.uk, gorcunov@...nvz.org,
	akpm@...ux-foundation.org, tim.c.chen@...ux.intel.com,
	devel@...nvz.org
Subject: Re: [RFC PATCH 0/5] net: socket bind to file descriptor introduced

On Wed, Aug 15, 2012 at 08:03:24PM -0700, Eric W. Biederman wrote:
> Stanislav Kinsbursky <skinsbursky@...allels.com> writes:
> 
> > This patch set introduces new socket operation and new system call:
> > sys_fbind(), which allows to bind socket to opened file.
> > File to bind to can be created by sys_mknod(S_IFSOCK) and opened by
> > open(O_PATH).
> >
> > This system call is especially required for UNIX sockets, which has name
> > lenght limitation.
> >
> > The following series implements...
> 
> Hmm.  I just realized this patchset is even sillier than I thought.
> 
> Stanislav is the problem you are ultimately trying to solve nfs clients
> in a container connecting to the wrong user space rpciod?
> 
> Aka net/sunrpc/xprtsock.c:xs_setup_local only taking an absolute path
> and then creating a delayed work item to actually open the unix domain
> socket?
> 
> The straight correct and straight forward thing to do appears to be:
> - Capture the root from current->fs in xs_setup_local.
> - In xs_local_finish_connect change current->fs.root to the captured
>   version of root before kernel_connect, and restore current->fs.root
>   after kernel_connect.

Ah, yep, that should do it.

--b.

> 
> It might not be a bad idea to implement open on unix domain sockets in
> a filesystem as create(AF_LOCAL)+connect() which would allow you to
> replace __sock_create + kernel_connect with a simple file_open_root.
> 
> But I think the simple scheme of:
> struct path old_root;
> old_root = current->fs.root;
> kernel_connect(...);
> current->fs.root = old_root;
> 
> Is more than sufficient and will remove the need for anything
> except a purely local change to get nfs clients to connect from
> containers.
> 
> Eric
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