linux-kernel - Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

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Message-ID: <50293BE9.3010408@parallels.com>
Date:	Mon, 13 Aug 2012 21:39:53 +0400
From:	Stanislav Kinsbursky <skinsbursky@...allels.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
CC:	Pavel Emelianov <xemul@...allels.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Trond.Myklebust@...app.com" <Trond.Myklebust@...app.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

13.08.2012 20:47, J. Bruce Fields пишет:
> On Sat, Aug 11, 2012 at 03:15:24PM +0400, Stanislav Kinsbursky wrote:
>> 11.08.2012 10:23, Pavel Emelyanov пишет:
>>> On 08/11/2012 03:09 AM, H. Peter Anvin wrote:
>>>> On 08/10/2012 12:28 PM, Alan Cox wrote:
>>>>> Explicitly for Linux yes - this is not generally true of the AF_UNIX
>>>>> socket domain and even the permissions aspect isn't guaranteed to be
>>>>> supported on some BSD environments !
>>>> Yes, but let's worry about what the Linux behavior should be.
>>>>
>>>>> The name is however just a proxy for the socket itself. You don't even
>>>>> get a device node in the usual sense or the same inode in the file system
>>>>> space.
>>>> No, but it is looked up the same way any other inode is (the difference
>>>> between FIFOs and sockets is that sockets have separate connections,
>>>> which is also why open() on sockets would be nice.)
>>>>
>>>> However, there is a fundamental difference between AF_UNIX sockets and
>>>> open(), and that is how the pathname is delivered.  It thus would make
>>>> more sense to provide the openat()-like information in struct
>>>> sockaddr_un, but that may be very hard to do in a sensible way.  In that
>>>> sense it perhaps would be cleaner to be able to do an open[at]() on the
>>>> socket node with O_PATH (perhaps there should be an O_SOCKET option,
>>>> even?) and pass the resulting file descriptor to bind() or connect().
>>> I vote for this (openat + O_WHATEVER on a unix socket) as well. It will
>>> help us in checkpoint-restore, making handling of overmounted/unlinked
>>> sockets much cleaner.
>> I have to notice, that it's not enough and doesn't solve the issue.
>> There should be some way how to connect/bind already existent unix
>> socket (from kernel, at least), because socket can be created in
>> user space.
>> And this way (sock operation or whatever) have to provide an ability
>> to lookup UNIX socket starting from specified root to support
>> containers.
> I don't understand--the rpcbind sockets are created by the kernel.  What
> am I missing?

Kernel preform connect to rpcbind socket (i.e. user-space binds it), 
doesn't it?

>
> --b.

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