So that NFS WRITE payloads can eventually be placed directly into a
file's page cache, enable the RPC-over-RDMA transport to present
these payloads in the xdr_buf's page list, while placing trailing
content (such as a GETATTR operation) in the xdr_buf's tail.

After this change, the RPC-over-RDMA's "copy tail" hack, added by
commit a97c331f ("svcrdma: Handle additional inline content"),
is no longer needed and can be removed.
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

Dan Carpenter <dan.carpenter@oracle.com> observed that the while()
loop in svc_rdma_build_read_chunk() does not document the assumption
that the loop interior is always executed at least once.

Defensive: the function now returns -EINVAL if this assumption
fails.
Suggested-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

Clean up: No need to save the I/O direction. The functions that
release svc_rdma_chunk_ctxt already know what direction to use.
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

Clean up: Use offset_in_page() macro instead of open-coding.
Reported-by: NGeliang Tang <geliangtang@gmail.com>
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

When an RPC-over-RDMA request is received, the Receive buffer
contains a Transport Header possibly followed by an RPC message.

Even though rq_arg.head[0] (as passed to NFSD) does not contain the
Transport Header header, currently rq_arg.len includes the size of
the Transport Header.

That violates the intent of the xdr_buf API contract. .buflen should
include everything, but .len should be exactly the length of the RPC
message in the buffer.

The rq_arg fields are summed together at the end of
svc_rdma_recvfrom to obtain the correct return value. rq_arg.len
really ought to contain the correct number of bytes already, but it
currently doesn't due to the above misbehavior.

Let's instead ensure that .buflen includes the length of the
transport header, and that .len is always equal to head.iov_len +
.page_len + tail.iov_len .
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

svc_rdma_rw.c already contains helpers for the sendto path.
Introduce helpers for the recvfrom path.

The plan is to replace the local NFSD bespoke code that constructs
and posts RDMA Read Work Requests with calls to the rdma_rw API.
This shares code with other RDMA-enabled ULPs that manages the gory
details of buffer registration and posting Work Requests.

This new code also puts all RDMA_NOMSG-specific logic in one place.

Lastly, the use of rqstp->rq_arg.pages is deprecated in favor of
using rqstp->rq_pages directly, for clarity.
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

Sanity case: Catch the case where more Work Requests are being
posted to the Send Queue than there are Send Queue Entries.

This might happen if a client sends a chunk with more segments than
there are SQEs for the transport. The server can't send that reply,
so the transport will deadlock unless the client drops the RPC.
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

The plan is to replace the local bespoke code that constructs and
posts RDMA Read and Write Work Requests with calls to the rdma_rw
API. This shares code with other RDMA-enabled ULPs that manages the
gory details of buffer registration and posting Work Requests.

Some design notes:

 o The structure of RPC-over-RDMA transport headers is flexible,
   allowing multiple segments per Reply with arbitrary alignment,
   each with a unique R_key. Write and Send WRs continue to be
   built and posted in separate code paths. However, one whole
   chunk (with one or more RDMA segments apiece) gets exactly
   one ib_post_send and one work completion.

 o svc_xprt reference counting is modified, since a chain of
   rdma_rw_ctx structs generates one completion, no matter how
   many Write WRs are posted.

 o The current code builds the transport header as it is construct-
   ing Write WRs. I've replaced that with marshaling of transport
   header data items in a separate step. This is because the exact
   structure of client-provided segments may not align with the
   components of the server's reply xdr_buf, or the pages in the
   page list. Thus parts of each client-provided segment may be
   written at different points in the send path.
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>