In very rare cases, an NFS READ operation might predict that the
non-payload part of the RPC Call is large. For instance, an
NFSv4 COMPOUND with a large GETATTR result, in combination with a
large Kerberos credential, could push the non-payload part to be
several kilobytes.
If the non-payload part is larger than the connection's inline
threshold, the client is required to provision a Reply chunk. The
current Linux client does not check for this case. There are two
obvious ways to handle it:
a. Provision a Write chunk for the payload and a Reply chunk for
the non-payload part
b. Provision a Reply chunk for the whole RPC Reply
Some testing at a recent NFS bake-a-thon showed that servers can
mostly handle a. but there are some corner cases that do not work
yet. b. already works (it has to, to handle krb5i/p), but could be
somewhat less efficient. However, I expect this scenario to be very
rare -- no-one has reported a problem yet.
So I'm going to implement b. Sometime later I will provide some
patches to help make b. a little more efficient by more carefully
choosing the Reply chunk's segment sizes to ensure the payload is
optimally aligned.
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
net/sunrpc/xprtrdma/rpc_rdma.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
index d18614e..7774aee 100644
--- a/net/sunrpc/xprtrdma/rpc_rdma.c
+++ b/net/sunrpc/xprtrdma/rpc_rdma.c
@@ -164,6 +164,21 @@ static bool rpcrdma_results_inline(struct rpcrdma_xprt *r_xprt,
return rqst->rq_rcv_buf.buflen <= ia->ri_max_inline_read;
}
+/* The client is required to provide a Reply chunk if the maximum
+ * size of the non-payload part of the RPC Reply is larger than
+ * the inline threshold.
+ */
+static bool
+rpcrdma_nonpayload_inline(const struct rpcrdma_xprt *r_xprt,
+ const struct rpc_rqst *rqst)
+{
+ const struct xdr_buf *buf = &rqst->rq_rcv_buf;
+ const struct rpcrdma_ia *ia = &r_xprt->rx_ia;
+
+ return buf->head[0].iov_len + buf->tail[0].iov_len <
+ ia->ri_max_inline_read;
+}
+
/* Split @vec on page boundaries into SGEs. FMR registers pages, not
* a byte range. Other modes coalesce these SGEs into a single MR
* when they can.
@@ -762,7 +777,8 @@ static bool rpcrdma_results_inline(struct rpcrdma_xprt *r_xprt,
*/
if (rpcrdma_results_inline(r_xprt, rqst))
wtype = rpcrdma_noch;
- else if (ddp_allowed && rqst->rq_rcv_buf.flags & XDRBUF_READ)
+ else if ((ddp_allowed && rqst->rq_rcv_buf.flags & XDRBUF_READ) &&
+ rpcrdma_nonpayload_inline(r_xprt, rqst))
wtype = rpcrdma_writech;
else
wtype = rpcrdma_replych;
