iomap: add a tracepoint for mappings returned by map_blocks

Add a new tracepoint so we can see what mapping the filesystem returns
to writeback a dirty page.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/iomap/buffered-io.c

@@ -1360,6 +1360,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 		error = wpc->ops->map_blocks(wpc, inode, pos);
 		if (error)
 			break;
+		trace_iomap_writepage_map(inode, &wpc->iomap);
 		if (WARN_ON_ONCE(wpc->iomap.type == IOMAP_INLINE))
 			continue;
 		if (wpc->iomap.type == IOMAP_HOLE)

fs/iomap/trace.h

@@ -148,6 +148,7 @@ DEFINE_EVENT(iomap_class, name,	\
 	TP_ARGS(inode, iomap))
 DEFINE_IOMAP_EVENT(iomap_iter_dstmap);
 DEFINE_IOMAP_EVENT(iomap_iter_srcmap);
+DEFINE_IOMAP_EVENT(iomap_writepage_map);
 
 TRACE_EVENT(iomap_iter,
 	TP_PROTO(struct iomap_iter *iter, const void *ops,