[GitHub/mt8127/android_kernel_alcatel_ttab.git] / Documentation / device-mapper / dm-flakey.txt

dm-flakey
=========

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 exhibits unreliable behaviour for <down
interval> seconds, and then this cycle repeats.

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
Commit	Line	Data
3407ef52 JB	1	dm-flakey
	2	=========
	3
b26f5e3d MS	4	This target is the same as the linear target except that it exhibits
	5	unreliable behaviour periodically. It's been found useful in simulating
	6	failing devices for testing purposes.
3407ef52 JB	7
3407ef52 JB	8	Starting from the time the table is loaded, the device is available for
b26f5e3d MS	9	<up interval> seconds, then exhibits unreliable behaviour for <down
b26f5e3d MS	10	interval> seconds, and then this cycle repeats.
3407ef52	11
b26f5e3d MS	12	Also, consider using this in combination with the dm-delay target too,
	13	which can delay reads and writes and/or send them to different
	14	underlying devices.
	15
	16	Table parameters
	17	----------------
	18	<dev path> <offset> <up interval> <down interval> \
	19	[<num_features> [<feature arguments>]]
	20
	21	Mandatory parameters:
3407ef52 JB	22	<dev path>: Full pathname to the underlying block-device, or a
	23	"major:minor" device-number.
	24	<offset>: Starting sector within the device.
	25	<up interval>: Number of seconds device is available.
	26	<down interval>: Number of seconds device returns errors.
b26f5e3d MS	27
	28	Optional feature parameters:
	29	If no feature parameters are present, during the periods of
	30	unreliability, all I/O returns errors.
	31
	32	drop_writes:
	33	All write I/O is silently ignored.
	34	Read I/O is handled correctly.
a3998799 MS	35
	36	corrupt_bio_byte <Nth_byte> <direction> <value> <flags>:
	37	During <down interval>, replace <Nth_byte> of the data of
	38	each matching bio with <value>.
	39
	40	<Nth_byte>: The offset of the byte to replace.
	41	Counting starts at 1, to replace the first byte.
	42	<direction>: Either 'r' to corrupt reads or 'w' to corrupt writes.
	43	'w' is incompatible with drop_writes.
	44	<value>: The value (from 0-255) to write.
	45	<flags>: Perform the replacement only if bio->bi_rw has all the
	46	selected flags set.
	47
	48	Examples:
	49	corrupt_bio_byte 32 r 1 0
	50	- replaces the 32nd byte of READ bios with the value 1
	51
	52	corrupt_bio_byte 224 w 0 32
	53	- replaces the 224th byte of REQ_META (=32) bios with the value 0