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

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Message-ID: <20121005200009.GA30139@fieldses.org>
Date:	Fri, 5 Oct 2012 16:00:09 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"hpa@...or.com" <hpa@...or.com>,
	"thierry.reding@...onic-design.de" <thierry.reding@...onic-design.de>,
	"bfields@...hat.com" <bfields@...hat.com>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	Pavel Emelianov <xemul@...allels.com>,
	"neilb@...e.de" <neilb@...e.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"paul.gortmaker@...driver.com" <paul.gortmaker@...driver.com>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"gorcunov@...nvz.org" <gorcunov@...nvz.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [RFC PATCH 0/5] net: socket bind to file descriptor introduced

On Tue, Sep 04, 2012 at 03:00:07PM -0400, bfields wrote:
> On Mon, Aug 20, 2012 at 02:18:13PM +0400, Stanislav Kinsbursky wrote:
> > 16.08.2012 07:03, Eric W. Biederman пишет:
> > >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?
> > >
> > 
> > Hi, Eric.
> > The problem you mentioned was the reason why I started to think about this.
> > But currently I believe, that limitations in unix sockets connect or
> > bind should be removed, because it will be useful it least for CRIU
> > project.
> > 
> > >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.
> > >
> > 
> > I like the idea of introducing new family (AF_LOCAL_AT for example)
> > and new sockaddr for connecting or binding from specified root. The
> > only thing I'm worrying is passing file descriptor to unix bind or
> > connect routine. Because this approach doesn't provide easy way to
> > use such family and sockaddr in kernel (like in NFS example).
> > 
> > >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.
> > >
> > 
> > That was my first idea.
> 
> So is this what you're planning on doing now?

What ever happened to this?

--b.

> 
> > And probably it would be worth to change all
> > fs_struct to support sockets with relative path.
> > What do you think about it?
> 
> I didn't understand the question.  Are you suggesting that changes to
> fs_struct would be required to make this work?  I don't see why.
> 
> --b.
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