75 lines
2.0 KiB
ReStructuredText
75 lines
2.0 KiB
ReStructuredText
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=========
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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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::
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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>:
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Full pathname to the underlying block-device, or a
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"major:minor" device-number.
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<offset>:
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Starting sector within the device.
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<up interval>:
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Number of seconds device is available.
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<down interval>:
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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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error_writes:
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All write I/O is failed with an error signalled.
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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>:
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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>:
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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>:
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The value (from 0-255) to write.
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<flags>:
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Perform the replacement only if bio->bi_opf has all the
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selected flags set.
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Examples:
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Replaces the 32nd byte of READ bios with the value 1::
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corrupt_bio_byte 32 r 1 0
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Replaces the 224th byte of REQ_META (=32) bios with the value 0::
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corrupt_bio_byte 224 w 0 32
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