The mds can inform the client not to use the IOMODE_RW layout
segment for doing READs. I.e., it is basically a
IOMODE_WRITE layout segment.
It would do this to not interfere with the WRITEs.
Signed-off-by: Tom Haynes <loghyr@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
It can return NULL if layoutgets are blocked currently. Fix it to return
-EAGAIN in that case, so we can properly handle it in pnfs_update_layout.
Also, clean up and simplify the error handling -- eliminate "status" and
just use "lseg".
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
There are several problems in the way a stateid is selected for a
LAYOUTGET operation:
We pick a stateid to use in the RPC prepare op, but that makes
it difficult to serialize LAYOUTGETs that use the open stateid. That
serialization is done in pnfs_update_layout, which occurs well before
the rpc_prepare operation.
Between those two events, the i_lock is dropped and reacquired.
pnfs_update_layout can find that the list has lsegs in it and not do any
serialization, but then later pnfs_choose_layoutget_stateid ends up
choosing the open stateid.
This patch changes the client to select the stateid to use in the
LAYOUTGET earlier, when we're searching for a usable layout segment.
This way we can do it all while holding the i_lock the first time, and
ensure that we serialize any LAYOUTGET call that uses a non-layout
stateid.
This also means a rework of how LAYOUTGET replies are handled, as we
must now get the latest stateid if we want to retransmit in response
to a retryable error.
Most of those errors boil down to the fact that the layout state has
changed in some fashion. Thus, what we really want to do is to re-search
for a layout when it fails with a retryable error, so that we can avoid
reissuing the RPC at all if possible.
While the LAYOUTGET RPC is async, the initiating thread always waits for
it to complete, so it's effectively synchronous anyway. Currently, when
we need to retry a LAYOUTGET because of an error, we drive that retry
via the rpc state machine.
This means that once the call has been submitted, it runs until it
completes. So, we must move the error handling for this RPC out of the
rpc_call_done operation and into the caller.
In order to handle errors like NFS4ERR_DELAY properly, we must also
pass a pointer to the sliding timeout, which is now moved to the stack
in pnfs_update_layout.
The complicating errors are -NFS4ERR_RECALLCONFLICT and
-NFS4ERR_LAYOUTTRYLATER, as those involve a timeout after which we give
up and return NULL back to the caller. So, there is some special
handling for those errors to ensure that the layers driving the retries
can handle that appropriately.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
If we get back something like NFS4ERR_OLD_STATEID, that will be
translated into -EAGAIN, and the do/while loop in send_layoutget
will drive the call again.
This is not quite what we want, I think. An error like that is a
sign that something has changed. That something could have been a
concurrent LAYOUTGET that would give us a usable lseg.
Lift the retry logic into pnfs_update_layout instead. That allows
us to redo the layout search, and may spare us from having to issue
an RPC.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Currently, the code will clear the fail bit if we get back a fatal
error. I don't think that's correct -- we want to clear that bit
if we do not get a fatal error.
Fixes: 0bcbf039f6 (nfs: handle request add failure properly)
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Setting just the NFS_LAYOUT_RETURN_REQUESTED flag doesn't do anything,
unless there are lsegs that are also being marked for return. At the
point where that happens this flag is also set, so these set_bit calls
don't do anything useful.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
LAYOUTRETURN is "special" in that servers and clients are expected to
work with old stateids. When the client sends a LAYOUTRETURN with an old
stateid in it then the server is expected to only tear down layout
segments that were present when that seqid was current. Ensure that the
client handles its accounting accordingly.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
When we want to selectively do a LAYOUTRETURN, we need to specify a
stateid that represents most recent layout acquisition that is to be
returned.
When we mark a layout stateid to be returned, we update the return
sequence number in the layout header with that value, if it's newer
than the existing one. Then, when we go to do a LAYOUTRETURN on
layout header put, we overwrite the seqid in the stateid with the
saved one, and then zero it out.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
In later patches, we're going to teach the client to be more selective
about how it returns layouts. This means keeping a record of what the
stateid's seqid was at the time that the server handed out a layout
segment.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Otherwise, we'll end up returning layouts that we've just received if
the client issues a new LAYOUTGET prior to the LAYOUTRETURN.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
If we are initializing reads or writes and can not connect to a DS, then
check whether or not IO is allowed through the MDS. If it is allowed,
reset to the MDS. Else, fail the layout segment and force a retry
of a new layout segment.
Signed-off-by: Tom Haynes <loghyr@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Whenever we check to see if we have the needed number of DSes for the
action, we may also have to check to see whether IO is allowed to go to
the MDS or not.
[jlayton: fix merge conflict due to lack of localio patches here]
Signed-off-by: Tom Haynes <loghyr@primarydata.com>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
This patch fixes a problem whereby the pNFS client falls back to doing
reads and writes through the metadata server even when the layout flag
FF_FLAGS_NO_IO_THRU_MDS is set.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
No need to make them a priority any more, or to make them succeed.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
When we're using a delegation to represent our open state, we should
ensure that we use the stateid that was used to create that delegation.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
In order to more easily distinguish what kind of stateid we are dealing
with, introduce a type that can be used to label the stateid structure.
The label will be useful both for debugging, but also when dealing with
operations like SETATTR, READ and WRITE that can take several different
types of stateid as arguments.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Clean up.
After "xprtrdma: Remove ro_unmap() from all registration modes",
there are no longer any sites that take rpcrdma_ia::qplock for read.
The one site that takes it for write is always single-threaded. It
is safe to remove it.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
In a cluster failover scenario, it is desirable for the client to
attempt to reconnect quickly, as an alternate NFS server is already
waiting to take over for the down server. The client can't see that
a server IP address has moved to a new server until the existing
connection is gone.
For fabrics and devices where it is meaningful, set a definite upper
bound on the amount of time before it is determined that a
connection is no longer valid. This allows the RPC client to detect
connection loss in a timely matter, then perform a fresh resolution
of the server GUID in case it has changed (cluster failover).
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Clean up: The ro_unmap method is no longer used.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
There needs to be a safe method of releasing registered memory
resources when an RPC terminates. Safe can mean a number of things:
+ Doesn't have to sleep
+ Doesn't rely on having a QP in RTS
ro_unmap_safe will be that safe method. It can be used in cases
where synchronous memory invalidation can deadlock, or needs to have
an active QP.
The important case is fencing an RPC's memory regions after it is
signaled (^C) and before it exits. If this is not done, there is a
window where the server can write an RPC reply into memory that the
client has released and re-used for some other purpose.
Note that this is a full solution for FRWR, but FMR and physical
still have some gaps where a particularly bad server can wreak
some havoc on the client. These gaps are not made worse by this
patch and are expected to be exceptionally rare and timing-based.
They are noted in documenting comments.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Separate the DMA unmap operation from freeing the MW. In a
subsequent patch they will not always be done at the same time,
and they are not related operations (except by order; freeing
the MW must be the last step during invalidation).
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
In a subsequent patch, the fr_xprt and fr_worker fields will be
needed by another memory registration mode. Move them into the
generic rpcrdma_mw structure that wraps struct rpcrdma_frmr.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Maintain the order of invalidation and DMA unmapping when doing
a background MR reset.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
frwr_op_unmap_sync() is now invoked in a workqueue context, the same
as __frwr_queue_recovery(). There's no need to defer MR reset if
posting LOCAL_INV MRs fails.
This means that even when ib_post_send() fails (which should occur
very rarely) the invalidation and DMA unmapping steps are still done
in the correct order.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Move the the I/O direction field from rpcrdma_mr_seg into the
rpcrdma_frmr.
This makes it possible to DMA-unmap the frwr long after an RPC has
exited and its rpcrdma_mr_seg array has been released and re-used.
This might occur if an RPC times out while waiting for a new
connection to be established.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Clean up: Follow same naming convention as other fields in struct
rpcrdma_frwr.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Clean up: Replace rpcrdma_flush_cqs() and rpcrdma_clean_cqs() with
the new ib_drain_qp() API.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-By: Leon Romanovsky <leonro@mellanox.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
rpcrdma_create_chunks() has been replaced, and can be removed.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
rpcrdma_marshal_req() makes a simplifying assumption: that NFS
operations with large Call messages have small Reply messages, and
vice versa. Therefore with RPC-over-RDMA, only one chunk type is
ever needed for each Call/Reply pair, because one direction needs
chunks, the other direction will always fit inline.
In fact, this assumption is asserted in the code:
if (rtype != rpcrdma_noch && wtype != rpcrdma_noch) {
dprintk("RPC: %s: cannot marshal multiple chunk lists\n",
__func__);
return -EIO;
}
But RPCGSS_SEC breaks this assumption. Because krb5i and krb5p
perform data transformation on RPC messages before they are
transmitted, direct data placement techniques cannot be used, thus
RPC messages must be sent via a Long call in both directions.
All such calls are sent with a Position Zero Read chunk, and all
such replies are handled with a Reply chunk. Thus the client must
provide every Call/Reply pair with both a Read list and a Reply
chunk.
Without any special security in effect, NFSv4 WRITEs may now also
use the Read list and provide a Reply chunk. The marshal_req
logic was preventing that, meaning an NFSv4 WRITE with a large
payload that included a GETATTR result larger than the inline
threshold would fail.
The code that encodes each chunk list is now completely contained in
its own function. There is some code duplication, but the trade-off
is that the overall logic should be more clear.
Note that all three chunk lists now share the rl_segments array.
Some additional per-req accounting is necessary to track this
usage. For the same reasons that the above simplifying assumption
has held true for so long, I don't expect more array elements are
needed at this time.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Update documenting comments to reflect code changes over the past
year.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Avoid the latency and interrupt overhead of registering a Write
chunk when handling NFS READ requests of a few hundred bytes or
less.
This change does not interoperate with Linux NFS/RDMA servers
that do not have commit 9d11b51ce7 ('svcrdma: Fix send_reply()
scatter/gather set-up'). Commit 9d11b51ce7 was introduced in v4.3,
and is included in 4.2.y, 4.1.y, and 3.18.y.
Oracle bug 22925946 has been filed to request that the above fix
be included in the Oracle Linux UEK4 NFS/RDMA server.
Red Hat bugzillas 1327280 and 1327554 have been filed to request
that RHEL NFS/RDMA server backports include the above fix.
Workaround: Replace the "proto=rdma,port=20049" mount options
with "proto=tcp" until commit 9d11b51ce7 is applied to your
NFS server.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
When deciding whether to send a Call inline, rpcrdma_marshal_req
doesn't take into account header bytes consumed by chunk lists.
This results in Call messages on the wire that are sometimes larger
than the inline threshold.
Likewise, when a Write list or Reply chunk is in play, the server's
reply has to emit an RDMA Send that includes a larger-than-minimal
RPC-over-RDMA header.
The actual size of a Call message cannot be estimated until after
the chunk lists have been registered. Thus the size of each
RPC-over-RDMA header can be estimated only after chunks are
registered; but the decision to register chunks is based on the size
of that header. Chicken, meet egg.
The best a client can do is estimate header size based on the
largest header that might occur, and then ensure that inline content
is always smaller than that.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Send buffer space is shared between the RPC-over-RDMA header and
an RPC message. A large RPC-over-RDMA header means less space is
available for the associated RPC message, which then has to be
moved via an RDMA Read or Write.
As more segments are added to the chunk lists, the header increases
in size. Typical modern hardware needs only a few segments to
convey the maximum payload size, but some devices and registration
modes may need a lot of segments to convey data payload. Sometimes
so many are needed that the remaining space in the Send buffer is
not enough for the RPC message. Sending such a message usually
fails.
To ensure a transport can always make forward progress, cap the
number of RDMA segments that are allowed in chunk lists. This
prevents less-capable devices and memory registrations from
consuming a large portion of the Send buffer by reducing the
maximum data payload that can be conveyed with such devices.
For now I choose an arbitrary maximum of 8 RDMA segments. This
allows a maximum size RPC-over-RDMA header to fit nicely in the
current 1024 byte inline threshold with over 700 bytes remaining
for an inline RPC message.
The current maximum data payload of NFS READ or WRITE requests is
one megabyte. To convey that payload on a client with 4KB pages,
each chunk segment would need to handle 32 or more data pages. This
is well within the capabilities of FMR. For physical registration,
the maximum payload size on platforms with 4KB pages is reduced to
32KB.
For FRWR, a device's maximum page list depth would need to be at
least 34 to support the maximum 1MB payload. A device with a smaller
maximum page list depth means the maximum data payload is reduced
when using that device.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Currently the sysctls that allow setting the inline threshold allow
any value to be set.
Small values only make the transport run slower. The default 1KB
setting is as low as is reasonable. And the logic that decides how
to divide a Send buffer between RPC-over-RDMA header and RPC message
assumes (but does not check) that the lower bound is not crazy (say,
57 bytes).
Send and receive buffers share a page with some control information.
Values larger than about 3KB can't be supported, currently.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
RPC-over-RDMA transports have a limit on how large a backward
direction (backchannel) RPC message can be. Ensure that the NFSv4.x
CREATE_SESSION operation advertises this limit to servers.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Commit 176e21ee2e ("SUNRPC: Support for RPC over AF_LOCAL
transports") added a 5-character netid, but did not bump
RPCBIND_MAXNETIDLEN from 4 to 5.
Fixes: 176e21ee2e ("SUNRPC: Support for RPC over AF_LOCAL ...")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
RFC 5666: The "rdma" netid is to be used when IPv4 addressing
is employed by the underlying transport, and "rdma6" for IPv6
addressing.
Add mount -o proto=rdma6 option to support NFS/RDMA IPv6 addressing.
Changes from v2:
- Integrated comments from Chuck Level, Anna Schumaker, Trodt Myklebust
- Add a little more to the patch description to describe NFS/RDMA
IPv6 suggested by Chuck Level and Anna Schumaker
- Removed duplicated rdma6 define
- Remove Opt_xprt_rdma mountfamily since it doesn't support
Signed-off-by: Shirley Ma <shirley.ma@oracle.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
OPEN_CREATE with EXCLUSIVE4_1 sends initial file permission.
Ignoring fact, that server have indicated that file mod is set, client
will send yet another SETATTR request, but, as mode is already set,
new SETATTR will be empty. This is not a problem, nevertheless
an extra roundtrip and slow open on high latency networks.
This change is aims to skip extra setattr after open if there are
no attributes to be set.
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
This adds the copy_range file_ops function pointer used by the
sys_copy_range() function call. This patch only implements sync copies,
so if an async copy happens we decode the stateid and ignore it.
Signed-off-by: Anna Schumaker <bjschuma@netapp.com>
Copy will use this to set up a commit request for a generic range. I
don't want to allocate a new pagecache entry for the file, so I needed
to change parts of the commit path to handle requests with a null
wb_page.
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
There's no guarantee that an IP address in a different network namespace
actually represents the same endpoint.
Also, if we allow unprivileged nfs mounts some day then this might allow
an unprivileged user in another network namespace to misdirect somebody
else's nfs mounts.
If sharing between containers is really what's wanted then that could
still be arranged explicitly, for example with bind mounts.
Reported-by: "Eric W. Biederman" <ebiederm@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
At Connectathon 2016, we found that recent upstream Linux clients
would occasionally send a LOCK operation with a zero stateid. This
appeared to happen in close proximity to another thread returning
a delegation before unlinking the same file while it remained open.
Earlier, the client received a write delegation on this file and
returned the open stateid. Now, as it is getting ready to unlink the
file, it returns the write delegation. But there is still an open
file descriptor on that file, so the client must OPEN the file
again before it returns the delegation.
Since commit 24311f8841 ('NFSv4: Recovery of recalled read
delegations is broken'), nfs_open_delegation_recall() clears the
NFS_DELEGATED_STATE flag _before_ it sends the OPEN. This allows a
racing LOCK on the same inode to be put on the wire before the OPEN
operation has returned a valid open stateid.
To eliminate this race, serialize delegation return with the
acquisition of a file lock on the same file. Adopt the same approach
as is used in the unlock path.
This patch also eliminates a similar race seen when sending a LOCK
operation at the same time as returning a delegation on the same file.
Fixes: 24311f8841 ('NFSv4: Recovery of recalled read ... ')
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
[Anna: Add sentence about LOCK / delegation race]
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
A mirror can be shared between multiple layouts, even with different
iomodes. That makes stats gathering simpler, but it causes a problem
when we get different creds in READ vs. RW layouts.
The current code drops the newer credentials onto the floor when this
occurs. That's problematic when you fetch a READ layout first, and then
a RW. If the READ layout doesn't have the correct creds to do a write,
then writes will fail.
We could just overwrite the READ credentials with the RW ones, but that
would break the ability for the server to fence the layout for reads if
things go awry. We need to be able to revert to the earlier READ creds
if the RW layout is returned afterward.
The simplest fix is to just keep two sets of creds per mirror. One for
READ layouts and one for RW, and then use the appropriate set depending
on the iomode of the layout segment.
Also fix up some RCU nits that sparse found.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
