Re: [PATCH] SUNRPC: set desired file system root before connectinglocal transports

[Stanislav Kinsbursky]

07.03.2012 04:19, Myklebust, Trond ÐÐÑÐÑ:
> 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@xxxxxxxxxxxxx>
> >
> > ---
> >   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?

Hi, Trond.
Looks like this is not a problem, because process fs->root->mnt usage counter 
was increased on transport creation.
IOW, transport holds current root and thus mount namespace can't disappear.

--
Best regards,
Stanislav Kinsbursky
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