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[v6,4/5] doc: document sysfs queue/independent_access_ranges attributes

Message ID 20210827075045.642269-5-damien.lemoal@wdc.com (mailing list archive)
State Superseded
Headers show
Series Initial support for multi-actuator HDDs | expand

Commit Message

Damien Le Moal Aug. 27, 2021, 7:50 a.m. UTC 
Update the file Documentation/block/queue-sysfs.rst to add a description
of a device queue sysfs entries related to independent access ranges
(e.g. concurrent positioning ranges for multi-actuator hard-disks).

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
---
 Documentation/block/queue-sysfs.rst | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
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Patch

diff --git a/Documentation/block/queue-sysfs.rst b/Documentation/block/queue-sysfs.rst
index 4dc7f0d499a8..17eef55434e7 100644
--- a/Documentation/block/queue-sysfs.rst
+++ b/Documentation/block/queue-sysfs.rst
@@ -286,4 +286,32 @@  sequential zones of zoned block devices (devices with a zoned attributed
 that reports "host-managed" or "host-aware"). This value is always 0 for
 regular block devices.
 
+independent_access_ranges (RO)
+------------------------------
+
+The presence of this sub-directory of the /sys/block/xxx/queue/ directory
+indicates that the device is capable of executing requests targeting
+different sector ranges in parallel. For instance, single LUN multi-actuator
+hard-disks will likely have an independent_access_ranges directory if the
+device correctly advertizes the sector ranges of its actuators.
+
+The independent_access_ranges directory contains one directory per access
+range, with each range described using the sector (RO) attribute file to
+indicate the first sector of the range and the nr_sectors (RO) attribute file
+to indicate the total number of sector in the range starting from the first
+sector of the range.  For example, a dual-actuator hard disk will have the
+following independent_access_ranges entries.::
+
+        $ tree /sys/block/<device>/queue/independent_access_ranges/
+        /sys/block/<device>/queue/independent_access_ranges/
+        |-- 0
+        |   |-- nr_sectors
+        |   `-- sector
+        `-- 1
+            |-- nr_sectors
+            `-- sector
+
+The sector and nr_sectors attributes use 512B sector unit, regardless of
+the actual block size of the device.
+
 Jens Axboe <jens.axboe@oracle.com>, February 2009