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Diffstat (limited to 'Documentation/device-mapper/dm-flakey.txt')
| -rw-r--r-- | Documentation/device-mapper/dm-flakey.txt | 48 |
1 files changed, 42 insertions, 6 deletions
diff --git a/Documentation/device-mapper/dm-flakey.txt b/Documentation/device-mapper/dm-flakey.txt index c8efdfd19a6..6ff5c232722 100644 --- a/Documentation/device-mapper/dm-flakey.txt +++ b/Documentation/device-mapper/dm-flakey.txt @@ -1,17 +1,53 @@ dm-flakey ========= -This target is the same as the linear target except that it returns I/O -errors periodically. It's been found useful in simulating failing -devices for testing purposes. +This target is the same as the linear target except that it exhibits +unreliable behaviour periodically. It's been found useful in simulating +failing devices for testing purposes. Starting from the time the table is loaded, the device is available for -<up interval> seconds, then returns errors for <down interval> seconds, -and then this cycle repeats. +<up interval> seconds, then exhibits unreliable behaviour for <down +interval> seconds, and then this cycle repeats. -Parameters: <dev path> <offset> <up interval> <down interval> +Also, consider using this in combination with the dm-delay target too, +which can delay reads and writes and/or send them to different +underlying devices. + +Table parameters +---------------- + <dev path> <offset> <up interval> <down interval> \ + [<num_features> [<feature arguments>]] + +Mandatory parameters: <dev path>: Full pathname to the underlying block-device, or a "major:minor" device-number. <offset>: Starting sector within the device. <up interval>: Number of seconds device is available. <down interval>: Number of seconds device returns errors. + +Optional feature parameters: + If no feature parameters are present, during the periods of + unreliability, all I/O returns errors. + + drop_writes: + All write I/O is silently ignored. + Read I/O is handled correctly. + + corrupt_bio_byte <Nth_byte> <direction> <value> <flags>: + During <down interval>, replace <Nth_byte> of the data of + each matching bio with <value>. + + <Nth_byte>: The offset of the byte to replace. + Counting starts at 1, to replace the first byte. + <direction>: Either 'r' to corrupt reads or 'w' to corrupt writes. + 'w' is incompatible with drop_writes. + <value>: The value (from 0-255) to write. + <flags>: Perform the replacement only if bio->bi_rw has all the + selected flags set. + +Examples: + corrupt_bio_byte 32 r 1 0 + - replaces the 32nd byte of READ bios with the value 1 + + corrupt_bio_byte 224 w 0 32 + - replaces the 224th byte of REQ_META (=32) bios with the value 0 |