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

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Date:	Wed, 7 Mar 2012 00:21:47 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
CC:	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"xemul@...allels.com" <xemul@...allels.com>,
	"neilb@...e.de" <neilb@...e.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jbottomley@...allels.com" <jbottomley@...allels.com>,
	"bfields@...ldses.org" <bfields@...ldses.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [PATCH] SUNRPC: set desired file system root before connecting
 local transports

On Wed, 2012-03-07 at 00:19 +0000, Myklebust, Trond wrote:
> On Wed, 2012-02-29 at 18:59 +0400, Stanislav Kinsbursky wrote:
> > Today, there is a problem in connecting of local SUNRPC thansports. These
> > transports uses UNIX sockets and connection itself is done by rpciod workqueue.
> > But UNIX sockets lookup is done in context of process file system root. I.e.
> > all local thunsports are connecting in rpciod context.
> > This works nice until we will try to mount NFS from process with other root -
> > for example in container. This container can have it's own (nested) root and
> > rcpbind process, listening on it's own unix sockets. But NFS mount attempt in
> > this container will register new service (Lockd for example) in global rpcbind
> > - not containers's one.
> > This patch solves the problem by switching rpciod kernel thread's file system
> > root to right one (stored on transport) while connecting of local transports.
> > 
> > Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
> > 
> > ---
> >  fs/fs_struct.c        |    1 +
> >  net/sunrpc/xprtsock.c |   32 ++++++++++++++++++++++++++++++--
> >  2 files changed, 31 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/fs_struct.c b/fs/fs_struct.c
> > index 78b519c..0f984c3 100644
> > --- a/fs/fs_struct.c
> > +++ b/fs/fs_struct.c
> > @@ -36,6 +36,7 @@ void set_fs_root(struct fs_struct *fs, struct path *path)
> >  	if (old_root.dentry)
> >  		path_put_longterm(&old_root);
> >  }
> > +EXPORT_SYMBOL_GPL(set_fs_root);
> >  
> >  /*
> >   * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
> > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > index 4c8281d..c94c181 100644
> > --- a/net/sunrpc/xprtsock.c
> > +++ b/net/sunrpc/xprtsock.c
> > @@ -37,6 +37,7 @@
> >  #include <linux/sunrpc/svcsock.h>
> >  #include <linux/sunrpc/xprtsock.h>
> >  #include <linux/file.h>
> > +#include <linux/fs_struct.h>
> >  #ifdef CONFIG_SUNRPC_BACKCHANNEL
> >  #include <linux/sunrpc/bc_xprt.h>
> >  #endif
> > @@ -255,6 +256,11 @@ struct sock_xprt {
> >  	void			(*old_state_change)(struct sock *);
> >  	void			(*old_write_space)(struct sock *);
> >  	void			(*old_error_report)(struct sock *);
> > +
> > +	/*
> > +	 * Saved transport creator root. Required for local transports only.
> > +	 */
> > +	struct path		root;
> >  };
> >  
> >  /*
> > @@ -1891,6 +1897,7 @@ static void xs_local_setup_socket(struct work_struct *work)
> >  	struct rpc_xprt *xprt = &transport->xprt;
> >  	struct socket *sock;
> >  	int status = -EIO;
> > +	struct path root;
> >  
> >  	if (xprt->shutdown)
> >  		goto out;
> > @@ -1908,7 +1915,14 @@ static void xs_local_setup_socket(struct work_struct *work)
> >  	dprintk("RPC:       worker connecting xprt %p via AF_LOCAL to %s\n",
> >  			xprt, xprt->address_strings[RPC_DISPLAY_ADDR]);
> >  
> > +	get_fs_root(current->fs, &root);
> > +	set_fs_root(current->fs, &transport->root);
> > +
> >  	status = xs_local_finish_connecting(xprt, sock);
> > +
> > +	set_fs_root(current->fs, &root);
> > +	path_put(&root);
> > +
> >  	switch (status) {
> >  	case 0:
> 
> Hi Stanislav,
> 
> What happens here if the mount namespace of the process that originally
> created the sock_xprt no longer exists? Should we care about that case?
> 
> Cheers
>   Trond

BTW: We will in any case need Al Viro and Christoph's ACK in order to
export the set_fs_root() function.

-- 
Trond Myklebust
Linux NFS client maintainer

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