path: root/Documentation/device-mapper/dm-flakey.txt
diff options
Diffstat (limited to 'Documentation/device-mapper/dm-flakey.txt')
1 files changed, 53 insertions, 0 deletions
diff --git a/Documentation/device-mapper/dm-flakey.txt b/Documentation/device-mapper/dm-flakey.txt
new file mode 100644
index 00000000..6ff5c232
--- /dev/null
+++ b/Documentation/device-mapper/dm-flakey.txt
@@ -0,0 +1,53 @@
+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.
+ 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