[PATCH RFC 2/5] SUNRPC: Add XDR overflow trace event

[Chuck Lever <chuck.lever@oracle.com>]

This can help field troubleshooting without needing the overhead of
a full network capture (ie, tcpdump).

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 include/trace/events/sunrpc.h |   67 +++++++++++++++++++++++++++++++++++++++++
 net/sunrpc/xdr.c              |   24 ++++++++++-----
 2 files changed, 84 insertions(+), 7 deletions(-)

diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index f88b0f52aa7e..fbc41b8142d3 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -254,6 +254,73 @@ TRACE_EVENT(rpc_stats_latency,
 		__entry->backlog, __entry->rtt, __entry->execute)
 );
 
+TRACE_EVENT(rpc_xdr_overflow,
+	TP_PROTO(
+		const struct xdr_stream *xdr,
+		size_t requested
+	),
+
+	TP_ARGS(xdr, requested),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, task_id)
+		__field(unsigned int, client_id)
+		__field(int, version)
+		__field(size_t, requested)
+		__field(const void *, end)
+		__field(const void *, p)
+		__field(const void *, head_base)
+		__field(size_t, head_len)
+		__field(const void *, tail_base)
+		__field(size_t, tail_len)
+		__field(unsigned int, page_len)
+		__field(unsigned int, len)
+		__string(progname,
+			 xdr->rqst->rq_task->tk_client->cl_program->name)
+		__string(procedure,
+			 xdr->rqst->rq_task->tk_msg.rpc_proc->p_name)
+	),
+
+	TP_fast_assign(
+		if (xdr->rqst) {
+			const struct rpc_task *task = xdr->rqst->rq_task;
+
+			__entry->task_id = task->tk_pid;
+			__entry->client_id = task->tk_client->cl_clid;
+			__assign_str(progname,
+				     task->tk_client->cl_program->name)
+			__entry->version = task->tk_client->cl_vers;
+			__assign_str(procedure, task->tk_msg.rpc_proc->p_name)
+		} else {
+			__entry->task_id = 0;
+			__entry->client_id = 0;
+			__assign_str(progname, "unknown")
+			__entry->version = 0;
+			__assign_str(procedure, "unknown")
+		}
+		__entry->requested = requested;
+		__entry->end = xdr->end;
+		__entry->p = xdr->p;
+		__entry->head_base = xdr->buf->head[0].iov_base,
+		__entry->head_len = xdr->buf->head[0].iov_len,
+		__entry->page_len = xdr->buf->page_len,
+		__entry->tail_base = xdr->buf->tail[0].iov_base,
+		__entry->tail_len = xdr->buf->tail[0].iov_len,
+		__entry->len = xdr->buf->len;
+	),
+
+	TP_printk(
+		"task:%u@%u %sv%d %s requested=%zu p=%p end=%p xdr=[%p,%zu]/%u/[%p,%zu]/%u\n",
+		__entry->task_id, __entry->client_id,
+		__get_str(progname), __entry->version, __get_str(procedure),
+		__entry->requested, __entry->p, __entry->end,
+		__entry->head_base, __entry->head_len,
+		__entry->page_len,
+		__entry->tail_base, __entry->tail_len,
+		__entry->len
+	)
+);
+
 /*
  * First define the enums in the below macros to be exported to userspace
  * via TRACE_DEFINE_ENUM().
diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 345f08b634ee..6d0b615a02ae 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -16,6 +16,7 @@
 #include <linux/sunrpc/xdr.h>
 #include <linux/sunrpc/msg_prot.h>
 #include <linux/bvec.h>
+#include <trace/events/sunrpc.h>
 
 /*
  * XDR functions for basic NFS types
@@ -554,9 +555,9 @@ static __be32 *xdr_get_next_encode_buffer(struct xdr_stream *xdr,
 	int frag1bytes, frag2bytes;
 
 	if (nbytes > PAGE_SIZE)
-		return NULL; /* Bigger buffers require special handling */
+		goto out_overflow; /* Bigger buffers require special handling */
 	if (xdr->buf->len + nbytes > xdr->buf->buflen)
-		return NULL; /* Sorry, we're totally out of space */
+		goto out_overflow; /* Sorry, we're totally out of space */
 	frag1bytes = (xdr->end - xdr->p) << 2;
 	frag2bytes = nbytes - frag1bytes;
 	if (xdr->iov)
@@ -585,6 +586,9 @@ static __be32 *xdr_get_next_encode_buffer(struct xdr_stream *xdr,
 	xdr->buf->page_len += frag2bytes;
 	xdr->buf->len += nbytes;
 	return p;
+out_overflow:
+	trace_rpc_xdr_overflow(xdr, nbytes);
+	return NULL;
 }
 
 /**
@@ -902,20 +906,23 @@ static __be32 *xdr_copy_to_scratch(struct xdr_stream *xdr, size_t nbytes)
 	size_t cplen = (char *)xdr->end - (char *)xdr->p;
 
 	if (nbytes > xdr->scratch.iov_len)
-		return NULL;
+		goto out_overflow;
 	p = __xdr_inline_decode(xdr, cplen);
 	if (p == NULL)
 		return NULL;
 	memcpy(cpdest, p, cplen);
+	if (!xdr_set_next_buffer(xdr))
+		goto out_overflow;
 	cpdest += cplen;
 	nbytes -= cplen;
-	if (!xdr_set_next_buffer(xdr))
-		return NULL;
 	p = __xdr_inline_decode(xdr, nbytes);
 	if (p == NULL)
 		return NULL;
 	memcpy(cpdest, p, nbytes);
 	return xdr->scratch.iov_base;
+out_overflow:
+	trace_rpc_xdr_overflow(xdr, nbytes);
+	return NULL;
 }
 
 /**
@@ -932,14 +939,17 @@ __be32 * xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes)
 {
 	__be32 *p;
 
-	if (nbytes == 0)
+	if (unlikely(nbytes == 0))
 		return xdr->p;
 	if (xdr->p == xdr->end && !xdr_set_next_buffer(xdr))
-		return NULL;
+		goto out_overflow;
 	p = __xdr_inline_decode(xdr, nbytes);
 	if (p != NULL)
 		return p;
 	return xdr_copy_to_scratch(xdr, nbytes);
+out_overflow:
+	trace_rpc_xdr_overflow(xdr, nbytes);
+	return NULL;
 }
 EXPORT_SYMBOL_GPL(xdr_inline_decode);