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doc: document sysfs queue/independent_access_ranges attributes

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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>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/r/20211027022223.183838-5-damien.lemoal@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Damien Le Moal 2021-10-27 11:22:22 +09:00 committed by Jens Axboe
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commit 6b3bae2324
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Documentation/block/queue-sysfs.rst
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@ -286,4 +286,35 @@ 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 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 sectors 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. Independent access ranges do not
overlap and include all sectors within the device capacity. The access
ranges are numbered in increasing order of the range start sector,
that is, the sector attribute of range 0 always has the value 0.
Jens Axboe <jens.axboe@oracle.com>, February 2009