rbd: include 'diff' command in man page

Signed-off-by: Sage Weil <sage@inktank.com>

diff --git a/doc/man/8/rbd.rst b/doc/man/8/rbd.rst
index 72b2db6304e4a58fef25e257852235ff158fe5ae..5c6f030ffe322dd566d7a5ddeb8b146e28081c27 100644 (file)
--- a/doc/man/8/rbd.rst
+++ b/doc/man/8/rbd.rst
@@ -180,6 +180,12 @@ Commands
   continuing.  If there was an end snapshot we verify it does not already exist before
   applying the changes, and create the snapshot when we are done.
 
+:command:`diff` [*image-name*] [--from-snap *snapname*]
+  Dump a list of byte extents in the image that have changed since the specified start
+  snapshot, or since the image was created.  Each output line includes the starting offset
+  (in bytes), the length of the region (in bytes), and either 'zero' or 'data' to indicate
+  whether the region is known to be zeros or may contain other data.
+
 :command:`cp` [*src-image*] [*dest-image*]
   Copies the content of a src-image into the newly created dest-image.
   dest-image will have the same size, order, and format as src-image.