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

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Message-ID: <507290DF.30307@parallels.com>
Date:	Mon, 8 Oct 2012 12:37:51 +0400
From:	Stanislav Kinsbursky <skinsbursky@...allels.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
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>,
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	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
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	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [RFC PATCH 0/5] net: socket bind to file descriptor introduced

06.10.2012 00:00, J. Bruce Fields пишет:
> 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?
>

Sorry, was busy.
I'll prepare patch today, I hope.

> --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.


-- 
Best regards,
Stanislav Kinsbursky
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