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.
?
--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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