If a clone image gets flattened while a parent read request is
underway, the original rbd object request needs to be resubmitted.
The reason is that by the time we get the response to the parent
read request, the data read from the parent may be out of date.
In other words, we could see this sequence of events:
rbd client parent image/osd
---------- ----------------
original object ENOENT;
issue parent read
respond to parent read
child image flattened
original image header refresh
<--- original object written independently here
parent read response received
Add code to rbd_img_parent_read_callback() to detect when a clone's
parent image has disappeared (as evidenced by its parent overlap
becoming 0), and re-submit the original read request in that case.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
02c74fbad9