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dm delay: add flush as a third class of IO

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Add a new class for dm-delay that delays flush requests.  Previously,
flushes were delayed as writes, but it caused problems if the user
needed to create a device with one or a few slow sectors for the purpose
of testing - all flushes would be forwarded to this device and delayed,
and that skews the test results.  Fix this by allowing to select 0 delay
for flushes.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Mikulas Patocka
2018-04-17 00:33:14 +02:00
committed by Mike Snitzer
parent 3876ac76f0
commit cda6b5ab7f
2 changed files with 32 additions and 5 deletions
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3
Documentation/device-mapper/delay.txt
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@@ -5,7 +5,8 @@ Device-Mapper's "delay" target delays reads and/or writes
and maps them to different devices.
Parameters:
<device> <offset> <delay> [<write_device> <write_offset> <write_delay>]
<device> <offset> <delay> [<write_device> <write_offset> <write_delay>
[<flush_device> <flush_offset> <flush_delay>]]
With separate write parameters, the first set is only used for reads.
Offsets are specified in sectors.