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

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Date:	Wed, 15 Aug 2012 20:03:24 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	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

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.

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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