From: Heinz Mauelshagen <heinzm@xxxxxxxxxx>
Signed-off-by: Heinz Mauelshagen <heinzm@xxxxxxxxxx>
---
.../admin-guide/device-mapper/delay.rst | 45 ++++++++++++++-----
1 file changed, 34 insertions(+), 11 deletions(-)
diff --git a/Documentation/admin-guide/device-mapper/delay.rst b/Documentation/admin-guide/device-mapper/delay.rst
index 917ba8c33359..53d79294e62a 100644
--- a/Documentation/admin-guide/device-mapper/delay.rst
+++ b/Documentation/admin-guide/device-mapper/delay.rst
@@ -3,29 +3,52 @@ dm-delay
========
Device-Mapper's "delay" target delays reads and/or writes
-and maps them to different devices.
+and/or flushs and optionally maps them to different devices.
-Parameters::
+Arguments::
<device> <offset> <delay> [<write_device> <write_offset> <write_delay>
[<flush_device> <flush_offset> <flush_delay>]]
-With separate write parameters, the first set is only used for reads.
+Table line has to either have 3, 6 or 9 arguments:
+
+3: apply offset and delay to read, write and flush operations on device
+
+6: apply offset and delay to device, also apply write_offset and write_delay
+ to write and flush operations on optionally different write_device with
+ optionally different sector offset
+
+9: same as 6 arguments plus define flush_offset and flush_delay explicitely
+ on/with optionally different flush_device/flush_offset.
+
Offsets are specified in sectors.
+
Delays are specified in milliseconds.
+
Example scripts
===============
::
-
- #!/bin/sh
- # Create device delaying rw operation for 500ms
- echo "0 `blockdev --getsz $1` delay $1 0 500" | dmsetup create delayed
+ #!/bin/sh
+ #
+ # Create mapped device named "delayed" delaying read, write and flush operations for 500ms.
+ #
+ dmsetup create delayed --table "0 `blockdev --getsz $1` delay $1 0 500"
::
+ #!/bin/sh
+ #
+ # Create mapped device delaying write and flush operations for 400ms and
+ # splitting reads to device $1 but writes and flushs to different device $2
+ # to different offsets of 2048 and 4096 sectors respectively.
+ #
+ dmsetup create delayed --table "0 `blockdev --getsz $1` delay $1 2048 0 $2 4096 400"
- #!/bin/sh
- # Create device delaying only write operation for 500ms and
- # splitting reads and writes to different devices $1 $2
- echo "0 `blockdev --getsz $1` delay $1 0 0 $2 0 500" | dmsetup create delayed
+::
+ #!/bin/sh
+ #
+ # Create mapped device delaying reads for 50ms, writes for 100ms and flushs for 333ms
+ # onto the same backing device at offset 0 sectors.
+ #
+ dmsetup create delayed --table "0 `blockdev --getsz $1` delay $1 0 50 $2 0 100 $1 0 333"
--
2.45.2
