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rpc: keep backchannel xprt as long as server connection

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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@redhat.com>
This commit is contained in:
J. Bruce Fields
2010-12-08 12:45:44 -05:00
parent d75faea330
commit 99de8ea962
3 changed files with 29 additions and 11 deletions
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2
net/sunrpc/xprt.c
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@@ -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);