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2018-09-30SUNRPC: Move RPC retransmission stat counter to xprt_transmit()Trond Myklebust1-7/+12
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Simplify xprt_prepare_transmit()Trond Myklebust1-16/+7
Remove the checks for whether or not we need to transmit, and whether or not a reply has been received. Those are already handled in call_transmit() itself. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Don't reset the request 'bytes_sent' counter when releasing XPRT_LOCKTrond Myklebust1-14/+0
If the request is still on the queue, this will be incorrect behaviour. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Treat the task and request as separate in the xprt_ops->send_request()Trond Myklebust1-1/+1
When we shift to using the transmit queue, then the task that holds the write lock will not necessarily be the same as the one being transmitted. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Fix up the back channel transmitTrond Myklebust1-1/+26
Fix up the back channel code to recognise that it has already been transmitted, so does not need to be called again. Also ensure that we set req->rq_task. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Refactor RPC call encodingTrond Myklebust1-9/+13
Move the call encoding so that it occurs before the transport connection etc. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Add a transmission queue for RPC requestsTrond Myklebust1-9/+75
Add the queue that will enforce the ordering of RPC task transmission. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Distinguish between the slot allocation list and receive queueTrond Myklebust1-6/+6
When storing a struct rpc_rqst on the slot allocation list, we currently use the same field 'rq_list' as we use to store the request on the receive queue. Since the structure is never on both lists at the same time, this is OK. However, for clarity, let's make that a union with different names for the different lists so that we can more easily distinguish between the two states. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Refactor xprt_transmit() to remove wait for reply codeTrond Myklebust1-22/+52
Allow the caller in clnt.c to call into the code to wait for a reply after calling xprt_transmit(). Again, the reason is that the backchannel code does not need this functionality. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Refactor xprt_transmit() to remove the reply queue codeTrond Myklebust1-44/+83
Separate out the action of adding a request to the reply queue so that the backchannel code can simply skip calling it altogether. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Rename xprt->recv_lock to xprt->queue_lockTrond Myklebust1-12/+12
We will use the same lock to protect both the transmit and receive queues. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Don't wake queued RPC calls multiple times in xprt_transmitTrond Myklebust1-6/+3
Rather than waking up the entire queue of RPC messages a second time, just wake up the task that was put to sleep. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Refactor the transport request pinningTrond Myklebust1-20/+23
We are going to need to pin for both send and receive. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Simplify identification of when the message send/receive is completeTrond Myklebust1-3/+14
Add states to indicate that the message send and receive are not yet complete. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: The transmitted message must lie in the RPCSEC window of validityTrond Myklebust1-0/+7
If a message has been encoded using RPCSEC_GSS, the server is maintaining a window of sequence numbers that it considers valid. The client should normally be tracking that window, and needs to verify that the sequence number used by the message being transmitted still lies inside the window of validity. So far, we've been able to assume this condition would be realised automatically, since the client has been encoding the message only after taking the socket lock. Once we change that condition, we will need the explicit check. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-09-30SUNRPC: Clean up initialisation of the struct rpc_rqstTrond Myklebust1-40/+51
Move the initialisation back into xprt.c. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-07-31sunrpc: whitespace fixesStephen Hemminger1-1/+1
Remove trailing whitespace and blank line at EOF Signed-off-by: Stephen Hemminger <stephen@networkplumber.org> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2018-06-19sunrpc: Prevent duplicate XID allocationChuck Lever1-3/+7
Krzysztof Kozlowski <krzk@kernel.org> reports that a heavy NFSv4 WRITE workload against a slow NFS server causes his Raspberry Pi clients to stall. Krzysztof bisected it to commit 37ac86c3a76c ("SUNRPC: Initialize rpc_rqst outside of xprt->reserve_lock") . I was able to reproduce similar behavior and it appears that rarely the RPC client layer is re-allocating an XID for an RPC that it has already partially sent. This results in the client ignoring the subsequent reply, which carries the original XID. For various reasons, checking !req->rq_xmit_bytes_sent in xprt_prepare_transmit is not a 100% reliable mechanism for determining when a fresh XID is needed. Trond's preference is to allocate the XID at the time each rpc_rqst slot is initialized. This patch should also address a gcc 4.1.2 complaint reported by Geert Uytterhoeven <geert@linux-m68k.org>. Reported-by: Krzysztof Kozlowski <krzk@kernel.org> Fixes: 37ac86c3a76c ("SUNRPC: Initialize rpc_rqst outside of ... ") Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Tested-by: Krzysztof Kozlowski <krzk@kernel.org> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-05-07SUNRPC: Add a ->free_slot transport calloutChuck Lever1-2/+3
Refactor: xprtrdma needs to have better control over when RPCs are awoken from the backlog queue, so replace xprt_free_slot with a transport op callout. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2018-05-07SUNRPC: Initialize rpc_rqst outside of xprt->reserve_lockChuck Lever1-5/+7
alloc_slot is a transport-specific op, but initializing an rpc_rqst is common to all transports. In addition, the only part of initial- izing an rpc_rqst that needs serialization is getting a fresh XID. Move rpc_rqst initialization to common code in preparation for adding a transport-specific alloc_slot to xprtrdma. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2018-04-10SUNRPC: Make num_reqs a non-atomic integerChuck Lever1-8/+9
If recording xprt->stat.max_slots is moved into xprt_alloc_slot, then xprt->num_reqs is never manipulated outside xprt->reserve_lock. There's no longer a need for xprt->num_reqs to be atomic. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2018-04-10SUNRPC: Make RTT measurement more precise (Send)Chuck Lever1-1/+0
Some RPC transports have more overhead in their send_request callouts than others. For example, for RPC-over-RDMA: - Marshaling an RPC often has to DMA map the RPC arguments - Registration methods perform memory registration as part of marshaling To capture just server and network latencies more precisely: when sending a Call, capture the rq_xtime timestamp _after_ the transport header has been marshaled. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2018-04-10SUNRPC: Make RTT measurement more precise (Receive)Chuck Lever1-2/+3
Some RPC transports have more overhead in their reply handlers than others. For example, for RPC-over-RDMA: - RPC completion has to wait for memory invalidation, which is not a part of the server/network round trip - Recently a context switch was introduced into the reply handler, which further artificially inflates the measure of RPC RTT To capture just server and network latencies more precisely: when receiving a reply, compute the RTT as soon as the XID is recognized rather than at RPC completion time. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2018-04-10SUNRPC: Move xprt_update_rtt callsiteChuck Lever1-3/+8
Since commit 33849792cbcd ("xprtrdma: Detect unreachable NFS/RDMA servers more reliably"), the xprtrdma transport now has a ->timer callout. But xprtrdma does not need to compute RTT data, only UDP needs that. Move the xprt_update_rtt call into the UDP transport implementation. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2018-02-07SUNRPC: Queue latency-sensitive socket tasks to xprtiodTrond Myklebust1-1/+2
The response to a write_space notification is very latency sensitive, so we should queue it to the lower latency xprtiod_workqueue. This is something we already do for the other cases where an rpc task holds the transport XPRT_LOCKED bitlock. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2018-01-23SUNRPC: Trace xprt_timer eventsChuck Lever1-1/+1
Track RPC timeouts: report the XID and the server address to match the content of network capture. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2017-12-16Merge tag 'nfs-for-4.15-3' of git://git.linux-nfs.org/projects/anna/linux-nfsLinus Torvalds1-9/+19
Pull NFS client fixes from Anna Schumaker: "This has two stable bugfixes, one to fix a BUG_ON() when nfs_commit_inode() is called with no outstanding commit requests and another to fix a race in the SUNRPC receive codepath. Additionally, there are also fixes for an NFS client deadlock and an xprtrdma performance regression. Summary: Stable bugfixes: - NFS: Avoid a BUG_ON() in nfs_commit_inode() by not waiting for a commit in the case that there were no commit requests. - SUNRPC: Fix a race in the receive code path Other fixes: - NFS: Fix a deadlock in nfs client initialization - xprtrdma: Fix a performance regression for small IOs" * tag 'nfs-for-4.15-3' of git://git.linux-nfs.org/projects/anna/linux-nfs: SUNRPC: Fix a race in the receive code path nfs: don't wait on commit in nfs_commit_inode() if there were no commit requests xprtrdma: Spread reply processing over more CPUs nfs: fix a deadlock in nfs client initialization
2017-12-15SUNRPC: Fix a race in the receive code pathTrond Myklebust1-9/+19
We must ensure that the call to rpc_sleep_on() in xprt_transmit() cannot race with the call to xprt_complete_rqst(). Reported-by: Chuck Lever <chuck.lever@oracle.com> Link: https://bugzilla.linux-nfs.org/show_bug.cgi?id=317 Fixes: ce7c252a8c74 ("SUNRPC: Add a separate spinlock to protect..") Cc: stable@vger.kernel.org # 4.14+ Reviewed-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2017-11-17Merge tag 'nfs-for-4.15-1' of git://git.linux-nfs.org/projects/anna/linux-nfsLinus Torvalds1-0/+1
Pull NFS client updates from Anna Schumaker: "Stable bugfixes: - Revalidate "." and ".." correctly on open - Avoid RCU usage in tracepoints - Fix ugly referral attributes - Fix a typo in nomigration mount option - Revert "NFS: Move the flock open mode check into nfs_flock()" Features: - Implement a stronger send queue accounting system for NFS over RDMA - Switch some atomics to the new refcount_t type Other bugfixes and cleanups: - Clean up access mode bits - Remove special-case revalidations in nfs_opendir() - Improve invalidating NFS over RDMA memory for async operations that time out - Handle NFS over RDMA replies with a worqueue - Handle NFS over RDMA sends with a workqueue - Fix up replaying interrupted requests - Remove dead NFS over RDMA definitions - Update NFS over RDMA copyright information - Be more consistent with bool initialization and comparisons - Mark expected switch fall throughs - Various sunrpc tracepoint cleanups - Fix various OPEN races - Fix a typo in nfs_rename() - Use common error handling code in nfs_lock_and_join_request() - Check that some structures are properly cleaned up during net_exit() - Remove net pointer from dprintk()s" * tag 'nfs-for-4.15-1' of git://git.linux-nfs.org/projects/anna/linux-nfs: (62 commits) NFS: Revert "NFS: Move the flock open mode check into nfs_flock()" NFS: Fix typo in nomigration mount option nfs: Fix ugly referral attributes NFS: super: mark expected switch fall-throughs sunrpc: remove net pointer from messages nfs: remove net pointer from messages sunrpc: exit_net cleanup check added nfs client: exit_net cleanup check added nfs/write: Use common error handling code in nfs_lock_and_join_requests() NFSv4: Replace closed stateids with the "invalid special stateid" NFSv4: nfs_set_open_stateid must not trigger state recovery for closed state NFSv4: Check the open stateid when searching for expired state NFSv4: Clean up nfs4_delegreturn_done NFSv4: cleanup nfs4_close_done NFSv4: Retry NFS4ERR_OLD_STATEID errors in layoutreturn pNFS: Retry NFS4ERR_OLD_STATEID errors in layoutreturn-on-close NFSv4: Don't try to CLOSE if the stateid 'other' field has changed NFSv4: Retry CLOSE and DELEGRETURN on NFS4ERR_OLD_STATEID. NFS: Fix a typo in nfs_rename() NFSv4: Fix open create exclusive when the server reboots ...
2017-11-17net: sunrpc: mark expected switch fall-throughsGustavo A. R. Silva1-0/+1
In preparation to enabling -Wimplicit-fallthrough, mark switch cases where we are expecting to fall through. Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2017-10-30Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller1-11/+25
Several conflicts here. NFP driver bug fix adding nfp_netdev_is_nfp_repr() check to nfp_fl_output() needed some adjustments because the code block is in an else block now. Parallel additions to net/pkt_cls.h and net/sch_generic.h A bug fix in __tcp_retransmit_skb() conflicted with some of the rbtree changes in net-next. The tc action RCU callback fixes in 'net' had some overlap with some of the recent tcf_block reworking. Signed-off-by: David S. Miller <davem@davemloft.net>
2017-10-19SUNRPC: Destroy transport from the system workqueueTrond Myklebust1-10/+24
The transport may need to flush transport connect and receive tasks that are running on rpciod. In order to do so safely, we need to ensure that the caller of cancel_work_sync() etc is not itself running on rpciod. Do so by running the destroy task from the system workqueue. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2017-10-18sunrpc: Convert timers to use timer_setup()Kees Cook1-5/+4
In preparation for unconditionally passing the struct timer_list pointer to all timer callbacks, switch to using the new timer_setup() and from_timer() to pass the timer pointer explicitly. Cc: Trond Myklebust <trond.myklebust@primarydata.com> Cc: Anna Schumaker <anna.schumaker@netapp.com> Cc: "J. Bruce Fields" <bfields@fieldses.org> Cc: Jeff Layton <jlayton@poochiereds.net> Cc: "David S. Miller" <davem@davemloft.net> Cc: linux-nfs@vger.kernel.org Cc: netdev@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2017-10-16SUNRPC: fix a list corruption issue in xprt_release()Trond Myklebust1-1/+1
We remove the request from the receive list before we call xprt_wait_on_pinned_rqst(), and so we need to use list_del_init(). Otherwise, we will see list corruption when xprt_complete_rqst() is called. Reported-by: Emre Celebi <emre@primarydata.com> Fixes: ce7c252a8c741 ("SUNRPC: Add a separate spinlock to protect...") Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2017-09-05xprtrdma: Use xprt_pin_rqst in rpcrdma_reply_handlerChuck Lever1-0/+2
Adopt the use of xprt_pin_rqst to eliminate contention between Call-side users of rb_lock and the use of rb_lock in rpcrdma_reply_handler. This replaces the mechanism introduced in 431af645cf66 ("xprtrdma: Fix client lock-up after application signal fires"). Use recv_lock to quickly find the completing rqst, pin it, then drop the lock. At that point invalidation and pull-up of the Reply XDR can be done. Both are often expensive operations. Finally, take recv_lock again to signal completion to the RPC layer. It also protects adjustment of "cwnd". This greatly reduces the amount of time a lock is held by the reply handler. Comparing lock_stat results shows a marked decrease in contention on rb_lock and recv_lock. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> [trond.myklebust@primarydata.com: Remove call to rpcrdma_buffer_put() from the "out_norqst:" path in rpcrdma_reply_handler.] Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2017-08-18SUNRPC: Add a separate spinlock to protect the RPC request receive listTrond Myklebust1-8/+12
This further reduces contention with the transport_lock, and allows us to convert to using a non-bh-safe spinlock, since the list is now never accessed from a bh context. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2017-08-16SUNRPC: Don't hold the transport lock across socket copy operationsTrond Myklebust1-0/+43
Instead add a mechanism to ensure that the request doesn't disappear from underneath us while copying from the socket. We do this by preventing xprt_release() from freeing the XDR buffers until the flag RPC_TASK_MSG_RECV has been cleared from the request. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com> Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
2017-07-13SUNRPC: Make slot allocation more reliableTrond Myklebust1-3/+5
In xprt_alloc_slot(), the spin lock is only needed to provide atomicity between the atomic_add_unless() failure and the call to xprt_add_backlog(). We do not actually need to hold it across the memory allocation itself. By dropping the lock, we can use a more resilient GFP_NOFS allocation, just as we now do in the rest of the RPC client code. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2017-04-25sunrpc: Export xprt_force_disconnect()Chuck Lever1-0/+1
xprt_force_disconnect() is already invoked from the socket transport. I want to invoke xprt_force_disconnect() from the RPC-over-RDMA transport, which is a separate module from sunrpc.ko. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2017-02-10sunrpc: Allow xprt->ops->timer method to sleepChuck Lever1-2/+0
The transport lock is needed to protect the xprt_adjust_cwnd() call in xs_udp_timer, but it is not necessary for accessing the rq_reply_bytes_recvd or tk_status fields. It is correct to sublimate the lock into UDP's xs_udp_timer method, where it is required. The ->timer method has to take the transport lock if needed, but it can now sleep safely, or even call back into the RPC scheduler. This is more a clean-up than a fix, but the "issue" was introduced by my transport switch patches back in 2005. Fixes: 46c0ee8bc4ad ("RPC: separate xprt_timer implementations") Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2016-12-01sunrpc: Don't engage exponential backoff when connection attempt is rejected.NeilBrown1-1/+2
xs_connect() contains an exponential backoff mechanism so the repeated connection attempts are delayed by longer and longer amounts. This is appropriate when the connection failed due to a timeout, but it not appropriate when a definitive "no" answer is received. In such cases, call_connect_status() imposes a minimum 3-second back-off, so not having the exponetial back-off will never result in immediate retries. The current situation is a problem when the NFS server tries to register with rpcbind but rpcbind isn't running. All connection attempts are made on the same "xprt" and as the connection is never "closed", the exponential back delays successive attempts to register, or de-register, different protocols. This results in a multi-minute delay with no benefit. So, when call_connect_status() receives a definitive "no", use xprt_conditional_disconnect() to cancel the previous connection attempt. This will set XPRT_CLOSE_WAIT so that xprt->ops->close() calls xs_close() which resets the reestablish_timeout. To ensure xprt_conditional_disconnect() does the right thing, we ensure that rq_connect_cookie is set before a connection attempt, and allow xprt_conditional_disconnect() to complete even when the transport is not fully connected. Signed-off-by: NeilBrown <neilb@suse.com> Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2016-09-19SUNRPC: Generalize the RPC buffer release APIChuck Lever1-1/+1
xprtrdma needs to allocate the Call and Reply buffers separately. TBH, the reliance on using a single buffer for the pair of XDR buffers is transport implementation-specific. Instead of passing just the rq_buffer into the buf_free method, pass the task structure and let buf_free take care of freeing both XDR buffers at once. There's a micro-optimization here. In the common case, both xprt_release and the transport's buf_free method were checking if rq_buffer was NULL. Now the check is done only once per RPC. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
2016-08-02SUNRPC: Fix up socket autodisconnectTrond Myklebust1-8/+18
Ensure that we don't forget to set up the disconnection timer for the case when a connect request is fulfilled after the RPC request that initiated it has timed out or been interrupted. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2016-06-13SUNRPC: Reduce latency when send queue is congestedTrond Myklebust1-2/+4
Use the low latency transport workqueue to process the task that is next in line on the xprt->sending queue. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2016-06-13SUNRPC: RPC transport queue must be low latencyTrond Myklebust1-4/+4
rpciod can easily get congested due to the long list of queued rpc_tasks. Having the receive queue wait in turn for those tasks to complete can therefore be a bottleneck. Address the problem by separating the workqueues into: - rpciod: manages rpc_tasks - xprtiod: manages transport related work. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2016-02-05SUNRPC: Use the multipath iterator to assign a transport to each taskTrond Myklebust1-11/+3
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2016-02-05SUNRPC: Add a structure to track multiple transportsTrond Myklebust1-0/+1
In order to support multipathing/trunking we will need the ability to track multiple transports. This patch sets up a basic structure for doing so. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2016-01-31SUNRPC: Make freeing of struct xprt rcu-safeTrond Myklebust1-1/+2
Have it call kfree_rcu() to ensure that we can use it on rcu-protected lists. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2016-01-31SUNRPC: Uninline xprt_get(); It isn't performance critical.Trond Myklebust1-3/+21
Also allow callers to pass NULL arguments to xprt_get() and xprt_put(). Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
2016-01-19svcrdma: Add class for RDMA backwards direction transportChuck Lever1-0/+1
To support the server-side of an NFSv4.1 backchannel on RDMA connections, add a transport class that enables backward direction messages on an existing forward channel connection. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Acked-by: Bruce Fields <bfields@fieldses.org> Signed-off-by: Doug Ledford <dledford@redhat.com>