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a3998799fb
Add corrupt_bio_byte feature to simulate corruption by overwriting a byte at a specified position with a specified value during intervals when the device is "down". Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
53 lines
1.9 KiB
Text
53 lines
1.9 KiB
Text
dm-flakey
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=========
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This target is the same as the linear target except that it exhibits
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unreliable behaviour periodically. It's been found useful in simulating
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failing devices for testing purposes.
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Starting from the time the table is loaded, the device is available for
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<up interval> seconds, then exhibits unreliable behaviour for <down
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interval> seconds, and then this cycle repeats.
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Also, consider using this in combination with the dm-delay target too,
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which can delay reads and writes and/or send them to different
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underlying devices.
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Table parameters
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----------------
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<dev path> <offset> <up interval> <down interval> \
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[<num_features> [<feature arguments>]]
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Mandatory parameters:
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<dev path>: Full pathname to the underlying block-device, or a
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"major:minor" device-number.
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<offset>: Starting sector within the device.
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<up interval>: Number of seconds device is available.
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<down interval>: Number of seconds device returns errors.
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Optional feature parameters:
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If no feature parameters are present, during the periods of
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unreliability, all I/O returns errors.
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drop_writes:
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All write I/O is silently ignored.
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Read I/O is handled correctly.
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corrupt_bio_byte <Nth_byte> <direction> <value> <flags>:
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During <down interval>, replace <Nth_byte> of the data of
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each matching bio with <value>.
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<Nth_byte>: The offset of the byte to replace.
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Counting starts at 1, to replace the first byte.
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<direction>: Either 'r' to corrupt reads or 'w' to corrupt writes.
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'w' is incompatible with drop_writes.
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<value>: The value (from 0-255) to write.
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<flags>: Perform the replacement only if bio->bi_rw has all the
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selected flags set.
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Examples:
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corrupt_bio_byte 32 r 1 0
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- replaces the 32nd byte of READ bios with the value 1
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corrupt_bio_byte 224 w 0 32
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- replaces the 224th byte of REQ_META (=32) bios with the value 0
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