doc/rgw: update reshard design regarding 'bucket sync disable'

Signed-off-by: Casey Bodley <[email protected]>

src/doc/rgw/multisite-reshard.md

@@ -72,10 +72,19 @@ The distinction between *index layout* and *log layout* is important, because in
 * Full sync uses a single bucket-wide listing to fetch all objects.
     - Use a cls_lock to prevent different shards from duplicating this work.
 * When incremental sync gets to the end of a log shard (i.e. listing the log returns truncated=false):
-    - If the remote has a newer log generation, flag that shard as 'resharded' in the bucket sync status.
-    - Once all shards in the current generation reach that 'resharded' state, incremental bucket sync can advance to the next generation.
+    - If the remote has a newer log generation, flag that shard as 'done' in the bucket sync status.
+    - Once all shards in the current generation reach that 'done' state, incremental bucket sync can advance to the next generation.
     - Use cls_version on the bucket sync status object to detect racing writes from other shards.
 
+### Bucket Sync Disable/Enable
+
+Reframe in terms of log generations, instead of handling SYNCSTOP events with a special Stopped state:
+
+* radosgw-admin bucket sync enable: create a new log generation in the bucket instance metadata
+    - detect races with reshard: fail if reshard in progress, and write with cls_version to detect race with start of reshard
+    - if the current log generation is shared with the bucket index layout (BucketLogType::InIndex), the new log generation will point at the same index layout/generation. so the log generation increments, but the index objects keep the same generation
+* SYNCSTOP in incremental sync: flag the shard as 'done' and ignore datalog events on that bucket until we see a new generation
+
 ### Log Trimming
 
 * Use generation number from sync status to trim the right logs