linux-kernel - Re: [PATCH 1/4] VFS: Add a VFS helper function vfs_remote_path

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Date:	Wed, 01 Apr 2009 09:06:28 -0400
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hch@...radead.org
Subject: Re: [PATCH 1/4] VFS: Add a VFS helper function
 vfs_remote_path_lookup()

On Wed, 2009-04-01 at 03:15 +0100, Al Viro wrote:
> On Wed, Mar 11, 2009 at 03:50:33PM -0400, Trond Myklebust wrote:
> > The purpose of this patch is to improve the mount path lookup support for
> > filesystems such as NFSv4, which require you to look up a mount path
> > string in a remote server's namespace.
> > 
> > Traversing such a path is pretty much identical to walking a local path,
> > in that it may involve following symlinks and even following referrals to
> > volumes that reside on other servers. Since the standard VFS path lookup
> > code already supports all these features (using in-kernel automounts for
> > following referrals) it would be nice to be able to reuse that code rather
> > than special case the mount path lookup in the NFS client.
> > 
> > This patch therefore defines a VFS helper function that sets up a temporary
> > mount namespace to represent the server namespace, and has the current
> > task pivot into that prior to doing the path lookup. Upon completion, it
> > pivots back into the original namespace, and destroys the private one.
> 
> NAK.  You are relying on too many things about caller (e.g. just what happens
> if you have shared fs_struct?  Does caller guarantee it won't happen?), so
> that's a bloody bad interface.  Open-code that sucker, then let's see what
> to do with surrounding code.  As it stands - no.

Since vfs_remote_path_lookup() creates a private copy of the fs_struct,
are you referring to the assumptions that are made in
create_private_mnt_ns()? Sure; that's not intended as an interface for
general use. I'll rewrite that...

Cheers
  Trond

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com
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