dm: add flakey target
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.
I needed a dm target to do some failure testing on btrfs's raid code, and
Mike pointed me at this.
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/Documentation/device-mapper/dm-flakey.txt b/Documentation/device-mapper/dm-flakey.txt
new file mode 100644
index 0000000..c8efdfd
--- /dev/null
+++ b/Documentation/device-mapper/dm-flakey.txt
@@ -0,0 +1,17 @@
+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.
+
+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.
+
+Parameters: <dev path> <offset> <up interval> <down interval>
+ <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.