I'm not understanding the snapshot part. It seems like most tests usinglog-writes do `_log_writes_replay_log_range $cur $SCRATCH_DEV >>$seqres.full` to start each iteration; and then it seems like this test can check the item counts before and after a _scratch_mount/_scratch_umount cycle and get the same results. (And, if that worked, the test wouldn'tneed its own _cleanup() and its own lv management, I think?) But I'm probably missing something.IIRC, the purpose of the snapshots is that the mount/unmount cycle is destructive in the middle of the operation. If the orphan is present, we'll blow up all the verity items, so if we did it on the device we were replaying onto, it would leave it in a messed up state as we kept replaying. So we snapshot at each entry and mount/unmount that to check the invariants.
I think what you're saying is that we can't use the device itself instead of the snapshot, because mount/unmount change the underlying device, and this definitely makes sense.
Looking at other dmlogwrites users, though, generic/482 looks like it does something similar, and I don't understand what the difference between the replay+snapshot+mount cycles here and the replay+mount cycles there. I probably just don't understand what the difference between the two tests' scenarios is, though.
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