rbd: send snapshot context with writes

Sending the right snapshot context with each write is required for
snapshots to work. Due to the ordering of calls, the snapshot context
is never set for any requests. This causes writes to the current
version of the image to be reflected in all snapshots, which are
supposed to be read-only.

This happens because rbd_osd_req_format_write() sets the snapshot
context based on obj_request->img_request. At this point, however,
obj_request->img_request has not been set yet, to the snapshot context
is set to NULL. Fix this by moving rbd_img_obj_request_add(), which
sets obj_request->img_request, before the osd request formatting
calls.

This resolves:
    http://tracker.ceph.com/issues/5465

Reported-by: Karol Jurak <karol.jurak@gmail.com>
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@linaro.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 7c66173e2d83..c8eb9cb77d36 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -2254,13 +2254,17 @@ static int rbd_img_request_fill(struct rbd_img_request *img_request,
                                         obj_request->pages, length,
                                         offset & ~PAGE_MASK, false, false);
 
+                /*
+                 * set obj_request->img_request before formatting
+                 * the osd_request so that it gets the right snapc
+                 */
+                rbd_img_obj_request_add(img_request, obj_request);
                 if (write_request)
                         rbd_osd_req_format_write(obj_request);
                 else
                         rbd_osd_req_format_read(obj_request);
 
                 obj_request->img_offset = img_offset;
-                rbd_img_obj_request_add(img_request, obj_request);
 
                 img_offset += length;
                 resid -= length;