linux-kernel - Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

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Message-ID: <20121009223139.GA25826@fieldses.org>
Date:	Tue, 9 Oct 2012 18:31:39 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Myklebust, Trond" <Trond.Myklebust@...app.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Stanislav Kinsbursky <skinsbursky@...allels.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [PATCH v3] SUNRPC: set desired file system root before
 connecting local transports

On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
> "Myklebust, Trond" <Trond.Myklebust@...app.com> writes:
> 
> > On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
> >> Cc'ing Eric since I seem to recall he suggested doing it this way?
> 
> Yes.  On second look setting fs->root won't work. We need to change fs.
> The problem is that by default all kernel threads share fs so changing
> fs->root will have non-local consequences.

Oh, huh.  And we can't "unshare" it somehow?

Or, previously you suggested:

	- introduce sockaddr_fd that can be applied to AF_UNIX sockets,
	  and teach unix_bind and unix_connect how to deal with a second
	  type of sockaddr, AT_FD:
	  struct sockaddr_fd { short fd_family; short pad; int fd; }

	- introduce sockaddr_unix_at that takes a directory file
	  descriptor as well as a unix path, and teach unix_bind and
	  unix_connect to deal with a second sockaddr type, AF_UNIX_AT:
	  struct sockaddr_unix_at { short family; short pad; int dfd; char path[102]; }

Any other options?

> I very much believe we want if at all possible to perform a local
> modification.
> 
> Changing fs isn't all that different from what devtmpfs is doing.

Sorry, I don't know much about devtmpfs, are you suggesting it as a
model?  What exactly should we look at?

--b.
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