I'm not understanding the snapshot part. It seems like most tests
using
log-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't
need 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.
