netfs: Adjust the netfs_failure tracepoint to indicate non-subreq lines

Adjust the netfs_failure tracepoint to indicate a subrequest number of -1
when it's a full-request failure unrelated to any particular subrequest,
such as a failure to encrypt its data buffer.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com

Link: https://lore.kernel.org/r/164623001948.3564931.2353852999649380059.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/164678204587.1200972.14893513018190383961.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/164692903233.2099075.15414355147237641274.stgit@warthog.procyon.org.uk/ # v3

Author: dhowells

include/trace/events/netfs.h

@@ -222,7 +222,7 @@ TRACE_EVENT(netfs_failure,
 
 	    TP_STRUCT__entry(
 		    __field(unsigned int,		rreq		)
-		    __field(unsigned short,		index		)
+		    __field(short,			index		)
 		    __field(short,			error		)
 		    __field(unsigned short,		flags		)
 		    __field(enum netfs_io_source,	source		)
@@ -234,17 +234,17 @@ TRACE_EVENT(netfs_failure,
 
 	    TP_fast_assign(
 		    __entry->rreq	= rreq->debug_id;
-		    __entry->index	= sreq ? sreq->debug_index : 0;
+		    __entry->index	= sreq ? sreq->debug_index : -1;
 		    __entry->error	= error;
 		    __entry->flags	= sreq ? sreq->flags : 0;
 		    __entry->source	= sreq ? sreq->source : NETFS_INVALID_READ;
 		    __entry->what	= what;
-		    __entry->len	= sreq ? sreq->len : 0;
+		    __entry->len	= sreq ? sreq->len : rreq->len;
 		    __entry->transferred = sreq ? sreq->transferred : 0;
 		    __entry->start	= sreq ? sreq->start : 0;
 			   ),
 
-	    TP_printk("R=%08x[%u] %s f=%02x s=%llx %zx/%zx %s e=%d",
+	    TP_printk("R=%08x[%d] %s f=%02x s=%llx %zx/%zx %s e=%d",
 		      __entry->rreq, __entry->index,
 		      __print_symbolic(__entry->source, netfs_sreq_sources),
 		      __entry->flags,