From 5d3691a8266e77fd2d695064532d0926af974331 Mon Sep 17 00:00:00 2001 From: Heinz Mauelshagen Date: Thu, 8 Aug 2024 13:50:36 +0200 Subject: [PATCH] dm delay: enhance kernel documentation This commit improves documentation of the dm-delay target. Signed-off-by: Heinz Mauelshagen Signed-off-by: Mikulas Patocka --- .../admin-guide/device-mapper/delay.rst | 41 +++++++++++++++---- 1 file changed, 32 insertions(+), 9 deletions(-) diff --git a/Documentation/admin-guide/device-mapper/delay.rst b/Documentation/admin-guide/device-mapper/delay.rst index 917ba8c333591..4d667228e7442 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:: [ [ ]] -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 + # + # 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 + # + # 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" -- 2.39.5