On Fri, Dec 10, 2010 at 07:20:13PM -0500, J. Bruce Fields wrote:
> On Wed, Dec 01, 2010 at 12:53:49PM -0500, bfields wrote:
> > This is just a small question about the nfsd-side backchannel code that
> > touches the rpc client code:
> >
> > There's nothing preventing multiple backchannels from sharing the same
> > tcp connection, either simultaneously or over time; from rfc 5661
> > section 2.10.3.1:
> >
> > A connection's association with a session is not exclusive. A
> > connection associated with the channel(s) of one session may be
> > simultaneously associated with the channel(s) of other sessions
> > including sessions associated with other client IDs.
> >
> > The current code creates a new rpc_xprt every time an rpc client is
> > created for a backchannel.
> >
> > But that's wrong: if two sessions share a backchannel, then they don't
> > necessarily want to share the same rpc_client, but they *do* need to
> > share the same rpc_xprt, to prevent xid reuse at least.
> >
> > So I think we should create one rpc_xprt the first time we use a
> > connection for a backchannel, and then keep it around as long as the
> > connection is open (in case the client reassociates it with a
> > backchannel again).
> >
> > rpc_clone_client() allows clients to share an rpc_xprt. I could use
> > that for example by keeping an nfsd-level data structure allowing me to
> > look up rpc_client's by connection.
> >
> > However, the server- and client- side xprt's already reference each
> > other--the client's pointer to the server is used to send requests, and
> > the server's pointer to the client is used to match incoming replies
> > with requests.
> >
> > So it would seem simplest to use the already existing pointer from the
> > svc_xprt back to the rpc_xprt.
> >
> > So, that would mean:
> >
> > - Allowing nfsd to create a client with the already-existing
> > rpc_xprt--maybe export rpc_new_client()? Or allow the
> > xprt->setup method to find an already-existing transport?
> > - Keeping any backchannel rpc_xprt around somehow as long as the
> > connection is open. Maybe let svc_xprt keep a reference on
> > the client xprt until svc_delete_xprt()??
>
> So that would be something like the following.
And I merged this with Chuck's git tree (including the xdr patches), and
ran some tests. No merge conflicts, and the tests passed.
--b.
>
> ?
>
> --b.
>
> commit 1eb4f46889940b861805742d67ba114e5de7ddf0
> Author: J. Bruce Fields <bfields@xxxxxxxxxx>
> Date: Tue Nov 30 19:15:01 2010 -0500
>
> rpc: move sk_bc_xprt to svc_xprt
>
> This seems obviously transport-level information even if it's currently
> used only by the server socket code.
>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
>
> diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
> index aea0d43..92ac407 100644
> --- a/include/linux/sunrpc/svc_xprt.h
> +++ b/include/linux/sunrpc/svc_xprt.h
> @@ -80,6 +80,7 @@ struct svc_xprt {
> struct list_head xpt_users; /* callbacks on free */
>
> struct net *xpt_net;
> + struct rpc_xprt *xpt_bc_xprt; /* NFSv4.1 backchannel */
> };
>
> static inline void unregister_xpt_user(struct svc_xprt *xpt, struct svc_xpt_user *u)
> diff --git a/include/linux/sunrpc/svcsock.h b/include/linux/sunrpc/svcsock.h
> index 1b353a7..04dba23 100644
> --- a/include/linux/sunrpc/svcsock.h
> +++ b/include/linux/sunrpc/svcsock.h
> @@ -28,7 +28,6 @@ struct svc_sock {
> /* private TCP part */
> u32 sk_reclen; /* length of record */
> u32 sk_tcplen; /* current read length */
> - struct rpc_xprt *sk_bc_xprt; /* NFSv4.1 backchannel xprt */
> };
>
> /*
> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> index 07919e1..5a27d09 100644
> --- a/net/sunrpc/svcsock.c
> +++ b/net/sunrpc/svcsock.c
> @@ -985,15 +985,17 @@ static int svc_process_calldir(struct svc_sock *svsk, struct svc_rqst *rqstp,
> vec[0] = rqstp->rq_arg.head[0];
> } else {
> /* REPLY */
> - if (svsk->sk_bc_xprt)
> - req = xprt_lookup_rqst(svsk->sk_bc_xprt, xid);
> + struct rpc_xprt *bc_xprt = svsk->sk_xprt.xpt_bc_xprt;
> +
> + if (bc_xprt)
> + req = xprt_lookup_rqst(bc_xprt, xid);
>
> if (!req) {
> printk(KERN_NOTICE
> "%s: Got unrecognized reply: "
> - "calldir 0x%x sk_bc_xprt %p xid %08x\n",
> + "calldir 0x%x xpt_bc_xprt %p xid %08x\n",
> __func__, ntohl(calldir),
> - svsk->sk_bc_xprt, xid);
> + bc_xprt, xid);
> vec[0] = rqstp->rq_arg.head[0];
> goto out;
> }
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index dfcab5a..18dc42e 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -2379,9 +2379,9 @@ static struct rpc_xprt *xs_setup_bc_tcp(struct xprt_create *args)
> * The backchannel uses the same socket connection as the
> * forechannel
> */
> + args->bc_xprt->xpt_bc_xprt = xprt;
> xprt->bc_xprt = args->bc_xprt;
> bc_sock = container_of(args->bc_xprt, struct svc_sock, sk_xprt);
> - bc_sock->sk_bc_xprt = xprt;
> transport->sock = bc_sock->sk_sock;
> transport->inet = bc_sock->sk_sk;
>
>
> commit 218a5c9b8fb3e9f33a3ef761dfaff2f9387686c4
> Author: J. Bruce Fields <bfields@xxxxxxxxxx>
> Date: Wed Dec 8 12:45:44 2010 -0500
>
> rpc: keep backchannel xprt as long as server connection
>
> Multiple backchannels can share the same tcp connection; from rfc 5661
> section 2.10.3.1:
>
> A connection's association with a session is not exclusive. A
> connection associated with the channel(s) of one session may be
> simultaneously associated with the channel(s) of other sessions
> including sessions associated with other client IDs.
>
> However, multiple backchannels share a connection, they must all share
> the same xid stream (hence the same rpc_xprt); the only way we have to
> match replies with calls at the rpc layer is using the xid.
>
> So, keep the rpc_xprt around as long as the connection lasts, in case
> we're asked to use the connection as a backchannel again.
>
> Requests to create new backchannel clients over a given server
> connection should results in creating new clients that reuse the
> existing rpc_xprt.
>
> But to start, just reject attempts to associate multiple rpc_xprt's with
> the same underlying bc_xprt.
>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
>
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index ea2ff78..597c79c 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -13,6 +13,7 @@
> #include <linux/sunrpc/stats.h>
> #include <linux/sunrpc/svc_xprt.h>
> #include <linux/sunrpc/svcsock.h>
> +#include <linux/sunrpc/xprt.h>
>
> #define RPCDBG_FACILITY RPCDBG_SVCXPRT
>
> @@ -128,6 +129,9 @@ static void svc_xprt_free(struct kref *kref)
> if (test_bit(XPT_CACHE_AUTH, &xprt->xpt_flags))
> svcauth_unix_info_release(xprt);
> put_net(xprt->xpt_net);
> + /* See comment on corresponding get in xs_setup_bc_tcp(): */
> + if (xprt->xpt_bc_xprt)
> + xprt_put(xprt->xpt_bc_xprt);
> xprt->xpt_ops->xpo_free(xprt);
> module_put(owner);
> }
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index 4c8f18a..749ad15 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -965,6 +965,7 @@ struct rpc_xprt *xprt_alloc(struct net *net, int size, int max_req)
> xprt = kzalloc(size, GFP_KERNEL);
> if (xprt == NULL)
> goto out;
> + kref_init(&xprt->kref);
>
> xprt->max_reqs = max_req;
> xprt->slot = kcalloc(max_req, sizeof(struct rpc_rqst), GFP_KERNEL);
> @@ -1102,7 +1103,6 @@ found:
> return xprt;
> }
>
> - kref_init(&xprt->kref);
> spin_lock_init(&xprt->transport_lock);
> spin_lock_init(&xprt->reserve_lock);
>
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index 18dc42e..0ef4dd4 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -2375,16 +2375,6 @@ static struct rpc_xprt *xs_setup_bc_tcp(struct xprt_create *args)
> xprt->reestablish_timeout = 0;
> xprt->idle_timeout = 0;
>
> - /*
> - * The backchannel uses the same socket connection as the
> - * forechannel
> - */
> - args->bc_xprt->xpt_bc_xprt = xprt;
> - xprt->bc_xprt = args->bc_xprt;
> - bc_sock = container_of(args->bc_xprt, struct svc_sock, sk_xprt);
> - transport->sock = bc_sock->sk_sock;
> - transport->inet = bc_sock->sk_sk;
> -
> xprt->ops = &bc_tcp_ops;
>
> switch (addr->sa_family) {
> @@ -2407,6 +2397,29 @@ static struct rpc_xprt *xs_setup_bc_tcp(struct xprt_create *args)
> xprt->address_strings[RPC_DISPLAY_PROTO]);
>
> /*
> + * The backchannel uses the same socket connection as the
> + * forechannel
> + */
> + if (args->bc_xprt->xpt_bc_xprt) {
> + /* XXX: actually, want to catch this case... */
> + ret = ERR_PTR(-EINVAL);
> + goto out_err;
> + }
> + /*
> + * Once we've associated a backchannel xprt with a connection,
> + * we want to keep it around as long as long as the connection
> + * lasts, in case we need to start using it for a backchannel
> + * again; this reference won't be dropped until bc_xprt is
> + * destroyed.
> + */
> + xprt_get(xprt);
> + args->bc_xprt->xpt_bc_xprt = xprt;
> + xprt->bc_xprt = args->bc_xprt;
> + bc_sock = container_of(args->bc_xprt, struct svc_sock, sk_xprt);
> + transport->sock = bc_sock->sk_sock;
> + transport->inet = bc_sock->sk_sk;
> +
> + /*
> * Since we don't want connections for the backchannel, we set
> * the xprt status to connected
> */
> @@ -2415,6 +2428,7 @@ static struct rpc_xprt *xs_setup_bc_tcp(struct xprt_create *args)
>
> if (try_module_get(THIS_MODULE))
> return xprt;
> + xprt_put(xprt);
> ret = ERR_PTR(-EINVAL);
> out_err:
> xprt_free(xprt);
>
> commit ba7febf8e1ff482a6dc535e08e550053d9e34a74
> Author: J. Bruce Fields <bfields@xxxxxxxxxx>
> Date: Wed Dec 8 13:48:19 2010 -0500
>
> rpc: allow xprt_class->setup to return a preexisting xprt
>
> This allows us to reuse the xprt associated with a server connection if
> one has already been set up.
>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
>
> diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
> index 89d10d2..bef0f53 100644
> --- a/include/linux/sunrpc/xprt.h
> +++ b/include/linux/sunrpc/xprt.h
> @@ -321,6 +321,7 @@ void xprt_conditional_disconnect(struct rpc_xprt *xprt, unsigned int cookie);
> #define XPRT_CLOSING (6)
> #define XPRT_CONNECTION_ABORT (7)
> #define XPRT_CONNECTION_CLOSE (8)
> +#define XPRT_INITIALIZED (9)
>
> static inline void xprt_set_connected(struct rpc_xprt *xprt)
> {
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index 749ad15..856274d 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -1102,6 +1102,9 @@ found:
> -PTR_ERR(xprt));
> return xprt;
> }
> + if (test_and_set_bit(XPRT_INITIALIZED, &xprt->state))
> + /* ->setup returned a pre-initialized xprt: */
> + return xprt;
>
> spin_lock_init(&xprt->transport_lock);
> spin_lock_init(&xprt->reserve_lock);
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index 0ef4dd4..4aced17 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -2359,6 +2359,15 @@ static struct rpc_xprt *xs_setup_bc_tcp(struct xprt_create *args)
> struct svc_sock *bc_sock;
> struct rpc_xprt *ret;
>
> + if (args->bc_xprt->xpt_bc_xprt) {
> + /*
> + * This server connection already has a backchannel
> + * export; we can't create a new one, as we wouldn't be
> + * able to match replies based on xid any more. So,
> + * reuse the already-existing one:
> + */
> + return args->bc_xprt->xpt_bc_xprt;
> + }
> xprt = xs_setup_xprt(args, xprt_tcp_slot_table_entries);
> if (IS_ERR(xprt))
> return xprt;
--
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