Starting with this patch it is possible to remove a
snapshot if there is only a one clone created from it.
In such case snapshot can be removed without any data
copying. This is achieved with following steps (case
with only one clone):
1. Open snapshot (Snapshot1) that shall be removed
2. Check if the Snapshot1 has no more than 1 clone (Clone1)
3. Remove Clone1 entry from Snapshot1
4. If the Snapshot1 has a parent snapshot (Snapshot2):
4a. Add Clone1 entry to the Snapshot2 clones list
4b. Remove Snapshot1 entry from Snapshot2 clones list
5. Open Clone1 blob
6. Freeze I/O operations on Clone1
7. Temporarily override md_ro flag for Snapshot1 and Clone1
for MD modification
8. Merge Snapshot1 and Clone1 clusters maps into Clone1
clusters map
9a. If Snapshot2 is present switch parent ID and backing
bs_dev on Clone1
9b. If Snapshot2 is not present set parent ID to
SPDK_BLOBID_INVALID and backing bs_dev to zeroes_dev
10. Sync MD on Clone1
11. Sync MD on Snapshot1
12. Restore MD flags for Clone1 and Snapshot1
13. Unfreeze I/O on Clone1
14. Close Clone1 blob
15. Remove Snapshot1
Signed-off-by: Maciej Szwed <maciej.szwed@intel.com>
Change-Id: I800724b981af894e01e1912d0077c5b34a2ae634
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/445576
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
622127d7e1