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-rw-r--r--Documentation/device-mapper/dm-flakey.txt29
1 files changed, 23 insertions, 6 deletions
diff --git a/Documentation/device-mapper/dm-flakey.txt b/Documentation/device-mapper/dm-flakey.txt
index c8efdfd19a65..1b66c868ee7e 100644
--- a/Documentation/device-mapper/dm-flakey.txt
+++ b/Documentation/device-mapper/dm-flakey.txt
@@ -1,17 +1,34 @@
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.