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authorRob Herring (Arm) <robh@kernel.org>2026-08-31 14:43:51 -0500
committerDmitry Torokhov <dmitry.torokhov@gmail.com>2026-09-13 18:17:31 -0700
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treef0b5f37b42fc13b9908a31b657c646b024231cdd /Documentation/admin-guide/device-mapper/delay.rst
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Input: tsc2007 - read "ti,poll-period" as u32grafted
The "ti,poll-period" property is documented as a normal uint32 cell. The driver used a u64 helper, which makes the helper type disagree with the schema even though the stored value is still small. Read "ti,poll-period" with the u32 helper matching the documented DT cell size. Assisted-by: Codex:gpt-5-5 Signed-off-by: Rob Herring (Arm) <robh@kernel.org> Link: https://patch.msgid.link/20260831194352.1185860-1-robh@kernel.org Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
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+========
+dm-delay
+========
+
+Device-Mapper's "delay" target delays reads and/or writes
+and/or flushes and optionally maps them to different devices.
+
+Arguments::
+
+ <device> <offset> <delay> [<write_device> <write_offset> <write_delay>
+ [<flush_device> <flush_offset> <flush_delay>]]
+
+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 explicitly
+ on/with optionally different flush_device/flush_offset.
+
+Offsets are specified in sectors.
+
+Delays are specified in milliseconds.
+
+
+Example scripts
+===============
+
+::
+ #!/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 flushes 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 mapped device delaying reads for 50ms, writes for 100ms and flushes 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"