rbd: do not read in parent info before snap context
Currently rbd_dev_v2_header_info() reads in parent info before the snap context is read in. This is wrong, because we may need to look at the the parent_overlap value of the snapshot instead of that of the base image, for example when mapping a snapshot - see next commit. (When mapping a snapshot, all we got is its name and we need the snap context to translate that name into an id to know which parent info to look for.) The approach taken here is to make sure rbd_dev_v2_parent_info() is called after the snap context has been read in. The other approach would be to add a parent_overlap field to struct rbd_mapping and maintain it the same way rbd_mapping::size is maintained. The reason I chose the first approach is that the value of keeping around both base image values and the actual mapping values is unclear to me. Signed-off-by: NIlya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: NAlex Elder <elder@linaro.org>
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