[PATCH v2 0/8] docs: consolidate sysfs-block into Documentation/ABI/

[PATCH v2 0/8] docs: consolidate sysfs-block into Documentation/ABI/

[Eric Biggers]

This series consolidates the documentation for /sys/block/<disk>/queue/
into Documentation/ABI/, where it is supposed to go (as per Greg KH:
https://lore.kernel.org/r/YaXXpEAwVGTLjp1e@kroah.com).

This series also updates MAINTAINERS to associate the block
documentation with the block layer.

This series applies to linux-block/for-next.

Changed v1 => v2:
   - Added patch which moves the documentation to the stable directory.
   - Added Reviewed-by tags.

Eric Biggers (8):
  docs: sysfs-block: move to stable directory
  docs: sysfs-block: sort alphabetically
  docs: sysfs-block: add contact for nomerges
  docs: sysfs-block: fill in missing documentation from queue-sysfs.rst
  docs: sysfs-block: document stable_writes
  docs: sysfs-block: document virt_boundary_mask
  docs: block: remove queue-sysfs.rst
  MAINTAINERS: add entries for block layer documentation

 Documentation/ABI/stable/sysfs-block  | 668 ++++++++++++++++++++++++++
 Documentation/ABI/testing/sysfs-block | 346 -------------
 Documentation/block/index.rst         |   1 -
 Documentation/block/queue-sysfs.rst   | 321 -------------
 MAINTAINERS                           |   2 +
 5 files changed, 670 insertions(+), 668 deletions(-)
 create mode 100644 Documentation/ABI/stable/sysfs-block
 delete mode 100644 Documentation/ABI/testing/sysfs-block
 delete mode 100644 Documentation/block/queue-sysfs.rst


base-commit: cb3b5daece093c8d921e4e8736c5d7eff1eeb98b
-- 
2.34.1

[PATCH v2 1/8] docs: sysfs-block: move to stable directory

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

The block layer sysfs ABI is widely used by userspace software and is
considered stable.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 Documentation/ABI/{testing => stable}/sysfs-block | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename Documentation/ABI/{testing => stable}/sysfs-block (100%)

diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/stable/sysfs-block
similarity index 100%
rename from Documentation/ABI/testing/sysfs-block
rename to Documentation/ABI/stable/sysfs-block
-- 
2.34.1

[PATCH v2 2/8] docs: sysfs-block: sort alphabetically

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Sort the documentation for the files alphabetically by file path so that
there is a logical order and it's clear where to add new files.

With two small exceptions, this patch doesn't change the documentation
itself and just reorders it:

- In /sys/block/<disk>/<part>/stat, I replaced <part> with <partition>
  to be consistent with the other files.
- The description for /sys/block/<disk>/<part>/stat referred to another
  file "above", which I reworded.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 Documentation/ABI/stable/sysfs-block | 385 ++++++++++++++-------------
 1 file changed, 203 insertions(+), 182 deletions(-)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index b16b0c45a272e..9febd53a5ebe8 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -1,31 +1,37 @@
-What:		/sys/block/<disk>/stat
-Date:		February 2008
-Contact:	Jerome Marchand <jmarchan@redhat.com>
+What:		/sys/block/<disk>/alignment_offset
+Date:		April 2009
+Contact:	Martin K. Petersen <martin.petersen@oracle.com>
 Description:
-		The /sys/block/<disk>/stat files displays the I/O
-		statistics of disk <disk>. They contain 11 fields:
+		Storage devices may report a physical block size that is
+		bigger than the logical block size (for instance a drive
+		with 4KB physical sectors exposing 512-byte logical
+		blocks to the operating system).  This parameter
+		indicates how many bytes the beginning of the device is
+		offset from the disk's natural alignment.
 
-		==  ==============================================
-		 1  reads completed successfully
-		 2  reads merged
-		 3  sectors read
-		 4  time spent reading (ms)
-		 5  writes completed
-		 6  writes merged
-		 7  sectors written
-		 8  time spent writing (ms)
-		 9  I/Os currently in progress
-		10  time spent doing I/Os (ms)
-		11  weighted time spent doing I/Os (ms)
-		12  discards completed
-		13  discards merged
-		14  sectors discarded
-		15  time spent discarding (ms)
-		16  flush requests completed
-		17  time spent flushing (ms)
-		==  ==============================================
 
-		For more details refer Documentation/admin-guide/iostats.rst
+What:		/sys/block/<disk>/discard_alignment
+Date:		May 2011
+Contact:	Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+		Devices that support discard functionality may
+		internally allocate space in units that are bigger than
+		the exported logical block size. The discard_alignment
+		parameter indicates how many bytes the beginning of the
+		device is offset from the internal allocation unit's
+		natural alignment.
+
+
+What:		/sys/block/<disk>/diskseq
+Date:		February 2021
+Contact:	Matteo Croce <mcroce@microsoft.com>
+Description:
+		The /sys/block/<disk>/diskseq files reports the disk
+		sequence number, which is a monotonically increasing
+		number assigned to every drive.
+		Some devices, like the loop device, refresh such number
+		every time the backing file is changed.
+		The value type is 64 bit unsigned.
 
 
 What:		/sys/block/<disk>/inflight
@@ -44,26 +50,12 @@ Description:
 		and for SCSI device also its queue_depth.
 
 
-What:		/sys/block/<disk>/diskseq
-Date:		February 2021
-Contact:	Matteo Croce <mcroce@microsoft.com>
-Description:
-		The /sys/block/<disk>/diskseq files reports the disk
-		sequence number, which is a monotonically increasing
-		number assigned to every drive.
-		Some devices, like the loop device, refresh such number
-		every time the backing file is changed.
-		The value type is 64 bit unsigned.
-
-
-What:		/sys/block/<disk>/<part>/stat
-Date:		February 2008
-Contact:	Jerome Marchand <jmarchan@redhat.com>
+What:		/sys/block/<disk>/integrity/device_is_integrity_capable
+Date:		July 2014
+Contact:	Martin K. Petersen <martin.petersen@oracle.com>
 Description:
-		The /sys/block/<disk>/<part>/stat files display the
-		I/O statistics of partition <part>. The format is the
-		same as the above-written /sys/block/<disk>/stat
-		format.
+		Indicates whether a storage device is capable of storing
+		integrity metadata. Set if the device is T10 PI-capable.
 
 
 What:		/sys/block/<disk>/integrity/format
@@ -74,6 +66,15 @@ Description:
 		E.g. T10-DIF-TYPE1-CRC.
 
 
+What:		/sys/block/<disk>/integrity/protection_interval_bytes
+Date:		July 2015
+Contact:	Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+		Describes the number of data bytes which are protected
+		by one integrity tuple. Typically the device's logical
+		block size.
+
+
 What:		/sys/block/<disk>/integrity/read_verify
 Date:		June 2008
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
@@ -91,21 +92,6 @@ Description:
 		512 bytes of data.
 
 
-What:		/sys/block/<disk>/integrity/device_is_integrity_capable
-Date:		July 2014
-Contact:	Martin K. Petersen <martin.petersen@oracle.com>
-Description:
-		Indicates whether a storage device is capable of storing
-		integrity metadata. Set if the device is T10 PI-capable.
-
-What:		/sys/block/<disk>/integrity/protection_interval_bytes
-Date:		July 2015
-Contact:	Martin K. Petersen <martin.petersen@oracle.com>
-Description:
-		Describes the number of data bytes which are protected
-		by one integrity tuple. Typically the device's logical
-		block size.
-
 What:		/sys/block/<disk>/integrity/write_generate
 Date:		June 2008
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
@@ -114,16 +100,6 @@ Description:
 		generate checksums for write requests bound for
 		devices that support receiving integrity metadata.
 
-What:		/sys/block/<disk>/alignment_offset
-Date:		April 2009
-Contact:	Martin K. Petersen <martin.petersen@oracle.com>
-Description:
-		Storage devices may report a physical block size that is
-		bigger than the logical block size (for instance a drive
-		with 4KB physical sectors exposing 512-byte logical
-		blocks to the operating system).  This parameter
-		indicates how many bytes the beginning of the device is
-		offset from the disk's natural alignment.
 
 What:		/sys/block/<disk>/<partition>/alignment_offset
 Date:		April 2009
@@ -136,76 +112,6 @@ Description:
 		indicates how many bytes the beginning of the partition
 		is offset from the disk's natural alignment.
 
-What:		/sys/block/<disk>/queue/logical_block_size
-Date:		May 2009
-Contact:	Martin K. Petersen <martin.petersen@oracle.com>
-Description:
-		This is the smallest unit the storage device can
-		address.  It is typically 512 bytes.
-
-What:		/sys/block/<disk>/queue/physical_block_size
-Date:		May 2009
-Contact:	Martin K. Petersen <martin.petersen@oracle.com>
-Description:
-		This is the smallest unit a physical storage device can
-		write atomically.  It is usually the same as the logical
-		block size but may be bigger.  One example is SATA
-		drives with 4KB sectors that expose a 512-byte logical
-		block size to the operating system.  For stacked block
-		devices the physical_block_size variable contains the
-		maximum physical_block_size of the component devices.
-
-What:		/sys/block/<disk>/queue/minimum_io_size
-Date:		April 2009
-Contact:	Martin K. Petersen <martin.petersen@oracle.com>
-Description:
-		Storage devices may report a granularity or preferred
-		minimum I/O size which is the smallest request the
-		device can perform without incurring a performance
-		penalty.  For disk drives this is often the physical
-		block size.  For RAID arrays it is often the stripe
-		chunk size.  A properly aligned multiple of
-		minimum_io_size is the preferred request size for
-		workloads where a high number of I/O operations is
-		desired.
-
-What:		/sys/block/<disk>/queue/optimal_io_size
-Date:		April 2009
-Contact:	Martin K. Petersen <martin.petersen@oracle.com>
-Description:
-		Storage devices may report an optimal I/O size, which is
-		the device's preferred unit for sustained I/O.  This is
-		rarely reported for disk drives.  For RAID arrays it is
-		usually the stripe width or the internal track size.  A
-		properly aligned multiple of optimal_io_size is the
-		preferred request size for workloads where sustained
-		throughput is desired.  If no optimal I/O size is
-		reported this file contains 0.
-
-What:		/sys/block/<disk>/queue/nomerges
-Date:		January 2010
-Contact:
-Description:
-		Standard I/O elevator operations include attempts to
-		merge contiguous I/Os. For known random I/O loads these
-		attempts will always fail and result in extra cycles
-		being spent in the kernel. This allows one to turn off
-		this behavior on one of two ways: When set to 1, complex
-		merge checks are disabled, but the simple one-shot merges
-		with the previous I/O request are enabled. When set to 2,
-		all merge tries are disabled. The default value is 0 -
-		which enables all types of merge tries.
-
-What:		/sys/block/<disk>/discard_alignment
-Date:		May 2011
-Contact:	Martin K. Petersen <martin.petersen@oracle.com>
-Description:
-		Devices that support discard functionality may
-		internally allocate space in units that are bigger than
-		the exported logical block size. The discard_alignment
-		parameter indicates how many bytes the beginning of the
-		device is offset from the internal allocation unit's
-		natural alignment.
 
 What:		/sys/block/<disk>/<partition>/discard_alignment
 Date:		May 2011
@@ -218,6 +124,30 @@ Description:
 		partition is offset from the internal allocation unit's
 		natural alignment.
 
+
+What:		/sys/block/<disk>/<partition>/stat
+Date:		February 2008
+Contact:	Jerome Marchand <jmarchan@redhat.com>
+Description:
+		The /sys/block/<disk>/<partition>/stat files display the
+		I/O statistics of partition <partition>. The format is the
+		same as the format of /sys/block/<disk>/stat.
+
+
+What:		/sys/block/<disk>/queue/chunk_sectors
+Date:		September 2016
+Contact:	Hannes Reinecke <hare@suse.com>
+Description:
+		chunk_sectors has different meaning depending on the type
+		of the disk. For a RAID device (dm-raid), chunk_sectors
+		indicates the size in 512B sectors of the RAID volume
+		stripe segment. For a zoned block device, either
+		host-aware or host-managed, chunk_sectors indicates the
+		size in 512B sectors of the zones of the device, with
+		the eventual exception of the last zone of the device
+		which may be smaller.
+
+
 What:		/sys/block/<disk>/queue/discard_granularity
 Date:		May 2011
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
@@ -231,6 +161,7 @@ Description:
 		physical block size. A discard_granularity of 0 means
 		that the device does not support discard functionality.
 
+
 What:		/sys/block/<disk>/queue/discard_max_bytes
 Date:		May 2011
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
@@ -247,6 +178,7 @@ Description:
 		value of 0 means that the device does not support
 		discard functionality.
 
+
 What:		/sys/block/<disk>/queue/discard_zeroes_data
 Date:		May 2011
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
@@ -254,6 +186,111 @@ Description:
 		Will always return 0.  Don't rely on any specific behavior
 		for discards, and don't read this file.
 
+
+What:		/sys/block/<disk>/queue/io_timeout
+Date:		November 2018
+Contact:	Weiping Zhang <zhangweiping@didiglobal.com>
+Description:
+		io_timeout is the request timeout in milliseconds. If a request
+		does not complete in this time then the block driver timeout
+		handler is invoked. That timeout handler can decide to retry
+		the request, to fail it or to start a device recovery strategy.
+
+
+What:		/sys/block/<disk>/queue/logical_block_size
+Date:		May 2009
+Contact:	Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+		This is the smallest unit the storage device can
+		address.  It is typically 512 bytes.
+
+
+What:		/sys/block/<disk>/queue/max_active_zones
+Date:		July 2020
+Contact:	Niklas Cassel <niklas.cassel@wdc.com>
+Description:
+		For zoned block devices (zoned attribute indicating
+		"host-managed" or "host-aware"), the sum of zones belonging to
+		any of the zone states: EXPLICIT OPEN, IMPLICIT OPEN or CLOSED,
+		is limited by this value. If this value is 0, there is no limit.
+
+
+What:		/sys/block/<disk>/queue/max_open_zones
+Date:		July 2020
+Contact:	Niklas Cassel <niklas.cassel@wdc.com>
+Description:
+		For zoned block devices (zoned attribute indicating
+		"host-managed" or "host-aware"), the sum of zones belonging to
+		any of the zone states: EXPLICIT OPEN or IMPLICIT OPEN,
+		is limited by this value. If this value is 0, there is no limit.
+
+
+What:		/sys/block/<disk>/queue/minimum_io_size
+Date:		April 2009
+Contact:	Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+		Storage devices may report a granularity or preferred
+		minimum I/O size which is the smallest request the
+		device can perform without incurring a performance
+		penalty.  For disk drives this is often the physical
+		block size.  For RAID arrays it is often the stripe
+		chunk size.  A properly aligned multiple of
+		minimum_io_size is the preferred request size for
+		workloads where a high number of I/O operations is
+		desired.
+
+
+What:		/sys/block/<disk>/queue/nomerges
+Date:		January 2010
+Contact:
+Description:
+		Standard I/O elevator operations include attempts to
+		merge contiguous I/Os. For known random I/O loads these
+		attempts will always fail and result in extra cycles
+		being spent in the kernel. This allows one to turn off
+		this behavior on one of two ways: When set to 1, complex
+		merge checks are disabled, but the simple one-shot merges
+		with the previous I/O request are enabled. When set to 2,
+		all merge tries are disabled. The default value is 0 -
+		which enables all types of merge tries.
+
+
+What:		/sys/block/<disk>/queue/nr_zones
+Date:		November 2018
+Contact:	Damien Le Moal <damien.lemoal@wdc.com>
+Description:
+		nr_zones indicates the total number of zones of a zoned block
+		device ("host-aware" or "host-managed" zone model). For regular
+		block devices, the value is always 0.
+
+
+What:		/sys/block/<disk>/queue/optimal_io_size
+Date:		April 2009
+Contact:	Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+		Storage devices may report an optimal I/O size, which is
+		the device's preferred unit for sustained I/O.  This is
+		rarely reported for disk drives.  For RAID arrays it is
+		usually the stripe width or the internal track size.  A
+		properly aligned multiple of optimal_io_size is the
+		preferred request size for workloads where sustained
+		throughput is desired.  If no optimal I/O size is
+		reported this file contains 0.
+
+
+What:		/sys/block/<disk>/queue/physical_block_size
+Date:		May 2009
+Contact:	Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+		This is the smallest unit a physical storage device can
+		write atomically.  It is usually the same as the logical
+		block size but may be bigger.  One example is SATA
+		drives with 4KB sectors that expose a 512-byte logical
+		block size to the operating system.  For stacked block
+		devices the physical_block_size variable contains the
+		maximum physical_block_size of the component devices.
+
+
 What:		/sys/block/<disk>/queue/write_same_max_bytes
 Date:		January 2012
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
@@ -267,6 +304,7 @@ Description:
 		write_same_max_bytes is 0, write same is not supported
 		by the device.
 
+
 What:		/sys/block/<disk>/queue/write_zeroes_max_bytes
 Date:		November 2016
 Contact:	Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
@@ -280,6 +318,7 @@ Description:
 		write_zeroes_max_bytes is 0, write zeroes is not supported
 		by the device.
 
+
 What:		/sys/block/<disk>/queue/zoned
 Date:		September 2016
 Contact:	Damien Le Moal <damien.lemoal@wdc.com>
@@ -297,50 +336,32 @@ Description:
 		zone commands, they will be treated as regular block
 		devices and zoned will report "none".
 
-What:		/sys/block/<disk>/queue/nr_zones
-Date:		November 2018
-Contact:	Damien Le Moal <damien.lemoal@wdc.com>
-Description:
-		nr_zones indicates the total number of zones of a zoned block
-		device ("host-aware" or "host-managed" zone model). For regular
-		block devices, the value is always 0.
 
-What:		/sys/block/<disk>/queue/max_active_zones
-Date:		July 2020
-Contact:	Niklas Cassel <niklas.cassel@wdc.com>
-Description:
-		For zoned block devices (zoned attribute indicating
-		"host-managed" or "host-aware"), the sum of zones belonging to
-		any of the zone states: EXPLICIT OPEN, IMPLICIT OPEN or CLOSED,
-		is limited by this value. If this value is 0, there is no limit.
-
-What:		/sys/block/<disk>/queue/max_open_zones
-Date:		July 2020
-Contact:	Niklas Cassel <niklas.cassel@wdc.com>
+What:		/sys/block/<disk>/stat
+Date:		February 2008
+Contact:	Jerome Marchand <jmarchan@redhat.com>
 Description:
-		For zoned block devices (zoned attribute indicating
-		"host-managed" or "host-aware"), the sum of zones belonging to
-		any of the zone states: EXPLICIT OPEN or IMPLICIT OPEN,
-		is limited by this value. If this value is 0, there is no limit.
+		The /sys/block/<disk>/stat files displays the I/O
+		statistics of disk <disk>. They contain 11 fields:
 
-What:		/sys/block/<disk>/queue/chunk_sectors
-Date:		September 2016
-Contact:	Hannes Reinecke <hare@suse.com>
-Description:
-		chunk_sectors has different meaning depending on the type
-		of the disk. For a RAID device (dm-raid), chunk_sectors
-		indicates the size in 512B sectors of the RAID volume
-		stripe segment. For a zoned block device, either
-		host-aware or host-managed, chunk_sectors indicates the
-		size in 512B sectors of the zones of the device, with
-		the eventual exception of the last zone of the device
-		which may be smaller.
+		==  ==============================================
+		 1  reads completed successfully
+		 2  reads merged
+		 3  sectors read
+		 4  time spent reading (ms)
+		 5  writes completed
+		 6  writes merged
+		 7  sectors written
+		 8  time spent writing (ms)
+		 9  I/Os currently in progress
+		10  time spent doing I/Os (ms)
+		11  weighted time spent doing I/Os (ms)
+		12  discards completed
+		13  discards merged
+		14  sectors discarded
+		15  time spent discarding (ms)
+		16  flush requests completed
+		17  time spent flushing (ms)
+		==  ==============================================
 
-What:		/sys/block/<disk>/queue/io_timeout
-Date:		November 2018
-Contact:	Weiping Zhang <zhangweiping@didiglobal.com>
-Description:
-		io_timeout is the request timeout in milliseconds. If a request
-		does not complete in this time then the block driver timeout
-		handler is invoked. That timeout handler can decide to retry
-		the request, to fail it or to start a device recovery strategy.
+		For more details refer Documentation/admin-guide/iostats.rst
-- 
2.34.1

[PATCH v2 3/8] docs: sysfs-block: add contact for nomerges

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

The nomerges file was missing a "Contact" entry.  Use linux-block.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 Documentation/ABI/stable/sysfs-block | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index 9febd53a5ebe8..c70fce6b76c17 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -242,7 +242,7 @@ Description:
 
 What:		/sys/block/<disk>/queue/nomerges
 Date:		January 2010
-Contact:
+Contact:	linux-block@vger.kernel.org
 Description:
 		Standard I/O elevator operations include attempts to
 		merge contiguous I/Os. For known random I/O loads these
-- 
2.34.1

[PATCH v2 4/8] docs: sysfs-block: fill in missing documentation from queue-sysfs.rst

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

sysfs documentation is supposed to go in Documentation/ABI/.
However, /sys/block/<disk>/queue/* are documented in
Documentation/block/queue-sysfs.rst, and sometimes redundantly in
Documentation/ABI/stable/sysfs-block too.

Let's consolidate this documentation into Documentation/ABI/.

Therefore, copy the relevant docs from queue-sysfs.rst into sysfs-block.

This primarily means adding the 25 missing files that were documented in
queue-sysfs.rst only, as well as mentioning the RO/RW status of files.

Documentation/ABI/ requires "Date" and "Contact" fields.  For the Date
fields, I used the date of the commit which added support for each file.
For the "Contact" fields, I used linux-block.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 Documentation/ABI/stable/sysfs-block | 482 +++++++++++++++++++++------
 1 file changed, 381 insertions(+), 101 deletions(-)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index c70fce6b76c17..de3b86a3dfa55 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -46,7 +46,7 @@ Description:
 		The value type is unsigned int.
 		Cf. Documentation/block/stat.rst which contains a single value for
 		requests in flight.
-		This is related to nr_requests in Documentation/block/queue-sysfs.rst
+		This is related to /sys/block/<disk>/queue/nr_requests
 		and for SCSI device also its queue_depth.
 
 
@@ -134,207 +134,487 @@ Description:
 		same as the format of /sys/block/<disk>/stat.
 
 
+What:		/sys/block/<disk>/queue/add_random
+Date:		June 2010
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] This file allows to turn off the disk entropy contribution.
+		Default value of this file is '1'(on).
+
+
 What:		/sys/block/<disk>/queue/chunk_sectors
 Date:		September 2016
 Contact:	Hannes Reinecke <hare@suse.com>
 Description:
-		chunk_sectors has different meaning depending on the type
+		[RO] chunk_sectors has different meaning depending on the type
 		of the disk. For a RAID device (dm-raid), chunk_sectors
-		indicates the size in 512B sectors of the RAID volume
-		stripe segment. For a zoned block device, either
-		host-aware or host-managed, chunk_sectors indicates the
-		size in 512B sectors of the zones of the device, with
-		the eventual exception of the last zone of the device
-		which may be smaller.
+		indicates the size in 512B sectors of the RAID volume stripe
+		segment. For a zoned block device, either host-aware or
+		host-managed, chunk_sectors indicates the size in 512B sectors
+		of the zones of the device, with the eventual exception of the
+		last zone of the device which may be smaller.
+
+
+What:		/sys/block/<disk>/queue/dax
+Date:		June 2016
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] This file indicates whether the device supports Direct
+		Access (DAX), used by CPU-addressable storage to bypass the
+		pagecache.  It shows '1' if true, '0' if not.
 
 
 What:		/sys/block/<disk>/queue/discard_granularity
 Date:		May 2011
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
 Description:
-		Devices that support discard functionality may
-		internally allocate space using units that are bigger
-		than the logical block size. The discard_granularity
-		parameter indicates the size of the internal allocation
-		unit in bytes if reported by the device. Otherwise the
-		discard_granularity will be set to match the device's
-		physical block size. A discard_granularity of 0 means
-		that the device does not support discard functionality.
+		[RO] Devices that support discard functionality may internally
+		allocate space using units that are bigger than the logical
+		block size. The discard_granularity parameter indicates the size
+		of the internal allocation unit in bytes if reported by the
+		device. Otherwise the discard_granularity will be set to match
+		the device's physical block size. A discard_granularity of 0
+		means that the device does not support discard functionality.
 
 
 What:		/sys/block/<disk>/queue/discard_max_bytes
 Date:		May 2011
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
 Description:
-		Devices that support discard functionality may have
-		internal limits on the number of bytes that can be
-		trimmed or unmapped in a single operation. Some storage
-		protocols also have inherent limits on the number of
-		blocks that can be described in a single command. The
-		discard_max_bytes parameter is set by the device driver
-		to the maximum number of bytes that can be discarded in
-		a single operation. Discard requests issued to the
-		device must not exceed this limit. A discard_max_bytes
-		value of 0 means that the device does not support
-		discard functionality.
+		[RW] While discard_max_hw_bytes is the hardware limit for the
+		device, this setting is the software limit. Some devices exhibit
+		large latencies when large discards are issued, setting this
+		value lower will make Linux issue smaller discards and
+		potentially help reduce latencies induced by large discard
+		operations.
+
+
+What:		/sys/block/<disk>/queue/discard_max_hw_bytes
+Date:		July 2015
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] Devices that support discard functionality may have
+		internal limits on the number of bytes that can be trimmed or
+		unmapped in a single operation.  The `discard_max_hw_bytes`
+		parameter is set by the device driver to the maximum number of
+		bytes that can be discarded in a single operation.  Discard
+		requests issued to the device must not exceed this limit.  A
+		`discard_max_hw_bytes` value of 0 means that the device does not
+		support discard functionality.
 
 
 What:		/sys/block/<disk>/queue/discard_zeroes_data
 Date:		May 2011
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
 Description:
-		Will always return 0.  Don't rely on any specific behavior
+		[RO] Will always return 0.  Don't rely on any specific behavior
 		for discards, and don't read this file.
 
 
+What:		/sys/block/<disk>/queue/fua
+Date:		May 2018
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] Whether or not the block driver supports the FUA flag for
+		write requests.  FUA stands for Force Unit Access. If the FUA
+		flag is set that means that write requests must bypass the
+		volatile cache of the storage device.
+
+
+What:		/sys/block/<disk>/queue/hw_sector_size
+Date:		January 2008
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] This is the hardware sector size of the device, in bytes.
+
+
+What:		/sys/block/<disk>/queue/independent_access_ranges/
+Date:		October 2021
+Contact:	linux-block@vger.kernel.org
+Description:
+		[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/<disk>/queue/independent_access_ranges/
+			/sys/block/<disk>/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.
+
+
+What:		/sys/block/<disk>/queue/io_poll
+Date:		November 2015
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] When read, this file shows whether polling is enabled (1)
+		or disabled (0).  Writing '0' to this file will disable polling
+		for this device.  Writing any non-zero value will enable this
+		feature.
+
+
+What:		/sys/block/<disk>/queue/io_poll_delay
+Date:		November 2016
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] If polling is enabled, this controls what kind of polling
+		will be performed. It defaults to -1, which is classic polling.
+		In this mode, the CPU will repeatedly ask for completions
+		without giving up any time.  If set to 0, a hybrid polling mode
+		is used, where the kernel will attempt to make an educated guess
+		at when the IO will complete. Based on this guess, the kernel
+		will put the process issuing IO to sleep for an amount of time,
+		before entering a classic poll loop. This mode might be a little
+		slower than pure classic polling, but it will be more efficient.
+		If set to a value larger than 0, the kernel will put the process
+		issuing IO to sleep for this amount of microseconds before
+		entering classic polling.
+
+
 What:		/sys/block/<disk>/queue/io_timeout
 Date:		November 2018
 Contact:	Weiping Zhang <zhangweiping@didiglobal.com>
 Description:
-		io_timeout is the request timeout in milliseconds. If a request
-		does not complete in this time then the block driver timeout
-		handler is invoked. That timeout handler can decide to retry
-		the request, to fail it or to start a device recovery strategy.
+		[RW] io_timeout is the request timeout in milliseconds. If a
+		request does not complete in this time then the block driver
+		timeout handler is invoked. That timeout handler can decide to
+		retry the request, to fail it or to start a device recovery
+		strategy.
+
+
+What:		/sys/block/<disk>/queue/iostats
+Date:		January 2009
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] This file is used to control (on/off) the iostats
+		accounting of the disk.
 
 
 What:		/sys/block/<disk>/queue/logical_block_size
 Date:		May 2009
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
 Description:
-		This is the smallest unit the storage device can
-		address.  It is typically 512 bytes.
+		[RO] This is the smallest unit the storage device can address.
+		It is typically 512 bytes.
 
 
 What:		/sys/block/<disk>/queue/max_active_zones
 Date:		July 2020
 Contact:	Niklas Cassel <niklas.cassel@wdc.com>
 Description:
-		For zoned block devices (zoned attribute indicating
+		[RO] For zoned block devices (zoned attribute indicating
 		"host-managed" or "host-aware"), the sum of zones belonging to
 		any of the zone states: EXPLICIT OPEN, IMPLICIT OPEN or CLOSED,
 		is limited by this value. If this value is 0, there is no limit.
 
+		If the host attempts to exceed this limit, the driver should
+		report this error with BLK_STS_ZONE_ACTIVE_RESOURCE, which user
+		space may see as the EOVERFLOW errno.
+
+
+What:		/sys/block/<disk>/queue/max_discard_segments
+Date:		February 2017
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] The maximum number of DMA scatter/gather entries in a
+		discard request.
+
+
+What:		/sys/block/<disk>/queue/max_hw_sectors_kb
+Date:		September 2004
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] This is the maximum number of kilobytes supported in a
+		single data transfer.
+
+
+What:		/sys/block/<disk>/queue/max_integrity_segments
+Date:		September 2010
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] Maximum number of elements in a DMA scatter/gather list
+		with integrity data that will be submitted by the block layer
+		core to the associated block driver.
+
 
 What:		/sys/block/<disk>/queue/max_open_zones
 Date:		July 2020
 Contact:	Niklas Cassel <niklas.cassel@wdc.com>
 Description:
-		For zoned block devices (zoned attribute indicating
+		[RO] For zoned block devices (zoned attribute indicating
 		"host-managed" or "host-aware"), the sum of zones belonging to
-		any of the zone states: EXPLICIT OPEN or IMPLICIT OPEN,
-		is limited by this value. If this value is 0, there is no limit.
+		any of the zone states: EXPLICIT OPEN or IMPLICIT OPEN, is
+		limited by this value. If this value is 0, there is no limit.
+
+
+What:		/sys/block/<disk>/queue/max_sectors_kb
+Date:		September 2004
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] This is the maximum number of kilobytes that the block
+		layer will allow for a filesystem request. Must be smaller than
+		or equal to the maximum size allowed by the hardware.
+
+
+What:		/sys/block/<disk>/queue/max_segment_size
+Date:		March 2010
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] Maximum size in bytes of a single element in a DMA
+		scatter/gather list.
+
+
+What:		/sys/block/<disk>/queue/max_segments
+Date:		March 2010
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] Maximum number of elements in a DMA scatter/gather list
+		that is submitted to the associated block driver.
 
 
 What:		/sys/block/<disk>/queue/minimum_io_size
 Date:		April 2009
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
 Description:
-		Storage devices may report a granularity or preferred
-		minimum I/O size which is the smallest request the
-		device can perform without incurring a performance
-		penalty.  For disk drives this is often the physical
-		block size.  For RAID arrays it is often the stripe
-		chunk size.  A properly aligned multiple of
-		minimum_io_size is the preferred request size for
-		workloads where a high number of I/O operations is
-		desired.
+		[RO] Storage devices may report a granularity or preferred
+		minimum I/O size which is the smallest request the device can
+		perform without incurring a performance penalty.  For disk
+		drives this is often the physical block size.  For RAID arrays
+		it is often the stripe chunk size.  A properly aligned multiple
+		of minimum_io_size is the preferred request size for workloads
+		where a high number of I/O operations is desired.
 
 
 What:		/sys/block/<disk>/queue/nomerges
 Date:		January 2010
 Contact:	linux-block@vger.kernel.org
 Description:
-		Standard I/O elevator operations include attempts to
-		merge contiguous I/Os. For known random I/O loads these
-		attempts will always fail and result in extra cycles
-		being spent in the kernel. This allows one to turn off
-		this behavior on one of two ways: When set to 1, complex
-		merge checks are disabled, but the simple one-shot merges
-		with the previous I/O request are enabled. When set to 2,
-		all merge tries are disabled. The default value is 0 -
-		which enables all types of merge tries.
+		[RW] Standard I/O elevator operations include attempts to merge
+		contiguous I/Os. For known random I/O loads these attempts will
+		always fail and result in extra cycles being spent in the
+		kernel. This allows one to turn off this behavior on one of two
+		ways: When set to 1, complex merge checks are disabled, but the
+		simple one-shot merges with the previous I/O request are
+		enabled. When set to 2, all merge tries are disabled. The
+		default value is 0 - which enables all types of merge tries.
+
+
+What:		/sys/block/<disk>/queue/nr_requests
+Date:		July 2003
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] This controls how many requests may be allocated in the
+		block layer for read or write requests. Note that the total
+		allocated number may be twice this amount, since it applies only
+		to reads or writes (not the accumulated sum).
+
+		To avoid priority inversion through request starvation, a
+		request queue maintains a separate request pool per each cgroup
+		when CONFIG_BLK_CGROUP is enabled, and this parameter applies to
+		each such per-block-cgroup request pool.  IOW, if there are N
+		block cgroups, each request queue may have up to N request
+		pools, each independently regulated by nr_requests.
 
 
 What:		/sys/block/<disk>/queue/nr_zones
 Date:		November 2018
 Contact:	Damien Le Moal <damien.lemoal@wdc.com>
 Description:
-		nr_zones indicates the total number of zones of a zoned block
-		device ("host-aware" or "host-managed" zone model). For regular
-		block devices, the value is always 0.
+		[RO] nr_zones indicates the total number of zones of a zoned
+		block device ("host-aware" or "host-managed" zone model). For
+		regular block devices, the value is always 0.
 
 
 What:		/sys/block/<disk>/queue/optimal_io_size
 Date:		April 2009
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
 Description:
-		Storage devices may report an optimal I/O size, which is
-		the device's preferred unit for sustained I/O.  This is
-		rarely reported for disk drives.  For RAID arrays it is
-		usually the stripe width or the internal track size.  A
-		properly aligned multiple of optimal_io_size is the
-		preferred request size for workloads where sustained
-		throughput is desired.  If no optimal I/O size is
-		reported this file contains 0.
+		[RO] Storage devices may report an optimal I/O size, which is
+		the device's preferred unit for sustained I/O.  This is rarely
+		reported for disk drives.  For RAID arrays it is usually the
+		stripe width or the internal track size.  A properly aligned
+		multiple of optimal_io_size is the preferred request size for
+		workloads where sustained throughput is desired.  If no optimal
+		I/O size is reported this file contains 0.
 
 
 What:		/sys/block/<disk>/queue/physical_block_size
 Date:		May 2009
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
 Description:
-		This is the smallest unit a physical storage device can
-		write atomically.  It is usually the same as the logical
-		block size but may be bigger.  One example is SATA
-		drives with 4KB sectors that expose a 512-byte logical
-		block size to the operating system.  For stacked block
-		devices the physical_block_size variable contains the
-		maximum physical_block_size of the component devices.
+		[RO] This is the smallest unit a physical storage device can
+		write atomically.  It is usually the same as the logical block
+		size but may be bigger.  One example is SATA drives with 4KB
+		sectors that expose a 512-byte logical block size to the
+		operating system.  For stacked block devices the
+		physical_block_size variable contains the maximum
+		physical_block_size of the component devices.
+
+
+What:		/sys/block/<disk>/queue/read_ahead_kb
+Date:		May 2004
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] Maximum number of kilobytes to read-ahead for filesystems
+		on this block device.
+
+
+What:		/sys/block/<disk>/queue/rotational
+Date:		January 2009
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] This file is used to stat if the device is of rotational
+		type or non-rotational type.
+
+
+What:		/sys/block/<disk>/queue/rq_affinity
+Date:		September 2008
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] If this option is '1', the block layer will migrate request
+		completions to the cpu "group" that originally submitted the
+		request. For some workloads this provides a significant
+		reduction in CPU cycles due to caching effects.
+
+		For storage configurations that need to maximize distribution of
+		completion processing setting this option to '2' forces the
+		completion to run on the requesting cpu (bypassing the "group"
+		aggregation logic).
+
+
+What:		/sys/block/<disk>/queue/scheduler
+Date:		October 2004
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] When read, this file will display the current and available
+		IO schedulers for this block device. The currently active IO
+		scheduler will be enclosed in [] brackets. Writing an IO
+		scheduler name to this file will switch control of this block
+		device to that new IO scheduler. Note that writing an IO
+		scheduler name to this file will attempt to load that IO
+		scheduler module, if it isn't already present in the system.
+
+
+What:		/sys/block/<disk>/queue/throttle_sample_time
+Date:		March 2017
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] This is the time window that blk-throttle samples data, in
+		millisecond.  blk-throttle makes decision based on the
+		samplings. Lower time means cgroups have more smooth throughput,
+		but higher CPU overhead. This exists only when
+		CONFIG_BLK_DEV_THROTTLING_LOW is enabled.
+
+
+What:		/sys/block/<disk>/queue/wbt_lat_usec
+Date:		November 2016
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] If the device is registered for writeback throttling, then
+		this file shows the target minimum read latency. If this latency
+		is exceeded in a given window of time (see wb_window_usec), then
+		the writeback throttling will start scaling back writes. Writing
+		a value of '0' to this file disables the feature. Writing a
+		value of '-1' to this file resets the value to the default
+		setting.
+
+
+What:		/sys/block/<disk>/queue/write_cache
+Date:		April 2016
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] When read, this file will display whether the device has
+		write back caching enabled or not. It will return "write back"
+		for the former case, and "write through" for the latter. Writing
+		to this file can change the kernels view of the device, but it
+		doesn't alter the device state. This means that it might not be
+		safe to toggle the setting from "write back" to "write through",
+		since that will also eliminate cache flushes issued by the
+		kernel.
 
 
 What:		/sys/block/<disk>/queue/write_same_max_bytes
 Date:		January 2012
 Contact:	Martin K. Petersen <martin.petersen@oracle.com>
 Description:
-		Some devices support a write same operation in which a
+		[RO] Some devices support a write same operation in which a
 		single data block can be written to a range of several
-		contiguous blocks on storage. This can be used to wipe
-		areas on disk or to initialize drives in a RAID
-		configuration. write_same_max_bytes indicates how many
-		bytes can be written in a single write same command. If
-		write_same_max_bytes is 0, write same is not supported
-		by the device.
+		contiguous blocks on storage. This can be used to wipe areas on
+		disk or to initialize drives in a RAID configuration.
+		write_same_max_bytes indicates how many bytes can be written in
+		a single write same command. If write_same_max_bytes is 0, write
+		same is not supported by the device.
 
 
 What:		/sys/block/<disk>/queue/write_zeroes_max_bytes
 Date:		November 2016
 Contact:	Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
 Description:
-		Devices that support write zeroes operation in which a
-		single request can be issued to zero out the range of
-		contiguous blocks on storage without having any payload
-		in the request. This can be used to optimize writing zeroes
-		to the devices. write_zeroes_max_bytes indicates how many
-		bytes can be written in a single write zeroes command. If
-		write_zeroes_max_bytes is 0, write zeroes is not supported
-		by the device.
+		[RO] Devices that support write zeroes operation in which a
+		single request can be issued to zero out the range of contiguous
+		blocks on storage without having any payload in the request.
+		This can be used to optimize writing zeroes to the devices.
+		write_zeroes_max_bytes indicates how many bytes can be written
+		in a single write zeroes command. If write_zeroes_max_bytes is
+		0, write zeroes is not supported by the device.
+
+
+What:		/sys/block/<disk>/queue/zone_append_max_bytes
+Date:		May 2020
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] This is the maximum number of bytes that can be written to
+		a sequential zone of a zoned block device using a zone append
+		write operation (REQ_OP_ZONE_APPEND). This value is always 0 for
+		regular block devices.
+
+
+What:		/sys/block/<disk>/queue/zone_write_granularity
+Date:		January 2021
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] This indicates the alignment constraint, in bytes, for
+		write operations in 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.
 
 
 What:		/sys/block/<disk>/queue/zoned
 Date:		September 2016
 Contact:	Damien Le Moal <damien.lemoal@wdc.com>
 Description:
-		zoned indicates if the device is a zoned block device
-		and the zone model of the device if it is indeed zoned.
-		The possible values indicated by zoned are "none" for
-		regular block devices and "host-aware" or "host-managed"
-		for zoned block devices. The characteristics of
-		host-aware and host-managed zoned block devices are
-		described in the ZBC (Zoned Block Commands) and ZAC
-		(Zoned Device ATA Command Set) standards. These standards
-		also define the "drive-managed" zone model. However,
-		since drive-managed zoned block devices do not support
-		zone commands, they will be treated as regular block
-		devices and zoned will report "none".
+		[RO] zoned indicates if the device is a zoned block device and
+		the zone model of the device if it is indeed zoned.  The
+		possible values indicated by zoned are "none" for regular block
+		devices and "host-aware" or "host-managed" for zoned block
+		devices. The characteristics of host-aware and host-managed
+		zoned block devices are described in the ZBC (Zoned Block
+		Commands) and ZAC (Zoned Device ATA Command Set) standards.
+		These standards also define the "drive-managed" zone model.
+		However, since drive-managed zoned block devices do not support
+		zone commands, they will be treated as regular block devices and
+		zoned will report "none".
 
 
 What:		/sys/block/<disk>/stat
-- 
2.34.1

[PATCH v2 5/8] docs: sysfs-block: document stable_writes

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

/sys/block/<disk>/queue/stable_writes is completely undocumented.
Document it.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 Documentation/ABI/stable/sysfs-block | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index de3b86a3dfa55..30ce8dc587bb2 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -516,6 +516,16 @@ Description:
 		scheduler module, if it isn't already present in the system.
 
 
+What:		/sys/block/<disk>/queue/stable_writes
+Date:		September 2020
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] If the device requires that memory must not be modified
+		while it is being written out to disk, this file will contain
+		'1'.  Otherwise it will contain '0'.  This file is writable for
+		testing purposes.
+
+
 What:		/sys/block/<disk>/queue/throttle_sample_time
 Date:		March 2017
 Contact:	linux-block@vger.kernel.org
-- 
2.34.1

Re: [PATCH v2 5/8] docs: sysfs-block: document stable_writes

[Bart Van Assche]

On 12/7/21 4:56 PM, Eric Biggers wrote:
> +What:		/sys/block/<disk>/queue/stable_writes
> +Date:		September 2020
> +Contact:	linux-block@vger.kernel.org
> +Description:
> +		[RW] If the device requires that memory must not be modified
> +		while it is being written out to disk, this file will contain
> +		'1'.  Otherwise it will contain '0'.  This file is writable for
> +		testing purposes.

Hmm ... doesn't this attribute apply to the process of transferring data from
host memory to the device instead of to writing to the disk? Whether data goes
to the storage device cache or to the storage medium itself depends on attributes
like FUA.

Thanks,

Bart.

Re: [PATCH v2 5/8] docs: sysfs-block: document stable_writes

[Eric Biggers]

On Wed, Dec 08, 2021 at 10:01:10AM -0800, Bart Van Assche wrote:
> On 12/7/21 4:56 PM, Eric Biggers wrote:
> > +What:		/sys/block/<disk>/queue/stable_writes
> > +Date:		September 2020
> > +Contact:	linux-block@vger.kernel.org
> > +Description:
> > +		[RW] If the device requires that memory must not be modified
> > +		while it is being written out to disk, this file will contain
> > +		'1'.  Otherwise it will contain '0'.  This file is writable for
> > +		testing purposes.
> 
> Hmm ... doesn't this attribute apply to the process of transferring data from
> host memory to the device instead of to writing to the disk? Whether data goes
> to the storage device cache or to the storage medium itself depends on attributes
> like FUA.
> 

Yes, I meant "written out to disk" in the general sense of writeback, not in the
sense of when the data reaches its final destination.  I'm not sure what the
best way to explain it is.  I think it's more than just "the process of
transferring data from host memory to the device", as that is just part of a
write request, whereas stable_writes applies to whole requests.  How about:

		[RW] This file will contain '1' if memory must not be modified
		while it is being used in a write request to this device.  When
		this is the case and the kernel is performing writeback of a
		page, the kernel will wait for writeback to complete before
		allowing the page to be modified again, rather than allowing
		immediate modification as is normally the case.  This
		restriction arises when the device accesses the memory multiple
		times where the same data must be seen every time -- for
		example, once to calculate a checksum and once to actually write
		the data.  If no such restriction exists, this file will contain
		'0'.  This file is writable for testing purposes.

- Eric

Re: [PATCH v2 5/8] docs: sysfs-block: document stable_writes

[Bart Van Assche]

On 12/8/21 2:34 PM, Eric Biggers wrote:
> Yes, I meant "written out to disk" in the general sense of writeback, not in the
> sense of when the data reaches its final destination.  I'm not sure what the
> best way to explain it is.  I think it's more than just "the process of
> transferring data from host memory to the device", as that is just part of a
> write request, whereas stable_writes applies to whole requests.  How about:
> 
> 		[RW] This file will contain '1' if memory must not be modified
> 		while it is being used in a write request to this device.  When
> 		this is the case and the kernel is performing writeback of a
> 		page, the kernel will wait for writeback to complete before
> 		allowing the page to be modified again, rather than allowing
> 		immediate modification as is normally the case.  This
> 		restriction arises when the device accesses the memory multiple
> 		times where the same data must be seen every time -- for
> 		example, once to calculate a checksum and once to actually write
> 		the data.  If no such restriction exists, this file will contain
> 		'0'.  This file is writable for testing purposes.

The above sounds good to me.

Thanks,

Bart.

[PATCH v2 6/8] docs: sysfs-block: document virt_boundary_mask

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

/sys/block/<disk>/queue/virt_boundary_mask is completely undocumented.
Document it.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 Documentation/ABI/stable/sysfs-block | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index 30ce8dc587bb2..e988742a54a4c 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -537,6 +537,17 @@ Description:
 		CONFIG_BLK_DEV_THROTTLING_LOW is enabled.
 
 
+What:		/sys/block/<disk>/queue/virt_boundary_mask
+Date:		April 2021
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] This file shows the I/O segment alignment mask for the
+		block device.  I/O requests to this device will be split between
+		segments wherever either the end of the previous segment or the
+		beginning of the current segment is not aligned to
+		virt_boundary_mask + 1 bytes.
+
+
 What:		/sys/block/<disk>/queue/wbt_lat_usec
 Date:		November 2016
 Contact:	linux-block@vger.kernel.org
-- 
2.34.1

Re: [PATCH v2 6/8] docs: sysfs-block: document virt_boundary_mask

[Bart Van Assche]

On 12/7/21 4:56 PM, Eric Biggers wrote:
> +What:		/sys/block/<disk>/queue/virt_boundary_mask
> +Date:		April 2021
> +Contact:	linux-block@vger.kernel.org
> +Description:
> +		[RO] This file shows the I/O segment alignment mask for the
> +		block device.  I/O requests to this device will be split between
> +		segments wherever either the end of the previous segment or the
> +		beginning of the current segment is not aligned to
> +		virt_boundary_mask + 1 bytes.

"I/O segment alignment" looks confusing to me. My understanding is that this
attribute refers to the alignment of the internal data buffer boundaries and not
to the alignment of the offset on the storage medium. The name "virt_boundary"
refers to the property that if all internal boundaries are a multiple of
(virt_boundary_mask + 1) then an MMU with page size (virt_boundary_mask + 1) can
map the entire data buffer onto a contiguous range of virtual addresses. E.g.
RDMA adapters have an MMU that can do this. Several drivers that set this
attribute support a storage controller that does not have an internal MMU. As an
example, the NVMe core sets this mask since the NVMe specification requires that
only the first element in a PRP list has a non-zero offset. From the NVMe
specification: "PRP entries contained within a PRP List shall have a memory page
offset of 0h. If a second PRP entry is present within a command, it shall have a
memory page offset of 0h. In both cases, the entries are memory".

Bart.

Re: [PATCH v2 6/8] docs: sysfs-block: document virt_boundary_mask

[Eric Biggers]

On Wed, Dec 08, 2021 at 10:33:19AM -0800, Bart Van Assche wrote:
> On 12/7/21 4:56 PM, Eric Biggers wrote:
> > +What:		/sys/block/<disk>/queue/virt_boundary_mask
> > +Date:		April 2021
> > +Contact:	linux-block@vger.kernel.org
> > +Description:
> > +		[RO] This file shows the I/O segment alignment mask for the
> > +		block device.  I/O requests to this device will be split between
> > +		segments wherever either the end of the previous segment or the
> > +		beginning of the current segment is not aligned to
> > +		virt_boundary_mask + 1 bytes.
> 
> "I/O segment alignment" looks confusing to me. My understanding is that this
> attribute refers to the alignment of the internal data buffer boundaries and not
> to the alignment of the offset on the storage medium. The name "virt_boundary"
> refers to the property that if all internal boundaries are a multiple of
> (virt_boundary_mask + 1) then an MMU with page size (virt_boundary_mask + 1) can
> map the entire data buffer onto a contiguous range of virtual addresses. E.g.
> RDMA adapters have an MMU that can do this. Several drivers that set this
> attribute support a storage controller that does not have an internal MMU. As an
> example, the NVMe core sets this mask since the NVMe specification requires that
> only the first element in a PRP list has a non-zero offset. From the NVMe
> specification: "PRP entries contained within a PRP List shall have a memory page
> offset of 0h. If a second PRP entry is present within a command, it shall have a
> memory page offset of 0h. In both cases, the entries are memory".

Sure, I meant for it to be talking about the memory addresses.  How about this:

		[RO] This file shows the I/O segment memory alignment mask for
		the block device.  I/O requests to this device will be split
		between segments wherever either the memory address of the end
		of the previous segment or the memory address of the beginning
		of the current segment is not aligned to virt_boundary_mask + 1
		bytes.

- Eric

Re: [PATCH v2 6/8] docs: sysfs-block: document virt_boundary_mask

[Bart Van Assche]

On 12/8/21 2:38 PM, Eric Biggers wrote:
> Sure, I meant for it to be talking about the memory addresses.  How about this:
> 
> 		[RO] This file shows the I/O segment memory alignment mask for
> 		the block device.  I/O requests to this device will be split
> 		between segments wherever either the memory address of the end
> 		of the previous segment or the memory address of the beginning
> 		of the current segment is not aligned to virt_boundary_mask + 1
> 		bytes.

That also sounds good to me.

Thanks,

Bart.

[PATCH v2 7/8] docs: block: remove queue-sysfs.rst

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

This has been replaced by Documentation/ABI/stable/sysfs-block, which is
the correct place for sysfs documentation.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 Documentation/block/index.rst       |   1 -
 Documentation/block/queue-sysfs.rst | 321 ----------------------------
 2 files changed, 322 deletions(-)
 delete mode 100644 Documentation/block/queue-sysfs.rst

diff --git a/Documentation/block/index.rst b/Documentation/block/index.rst
index 86dcf7159f990..3a41495dd77b5 100644
--- a/Documentation/block/index.rst
+++ b/Documentation/block/index.rst
@@ -20,7 +20,6 @@ Block
    kyber-iosched
    null_blk
    pr
-   queue-sysfs
    request
    stat
    switching-sched
diff --git a/Documentation/block/queue-sysfs.rst b/Documentation/block/queue-sysfs.rst
deleted file mode 100644
index 3f569d5324857..0000000000000
--- a/Documentation/block/queue-sysfs.rst
+++ /dev/null
@@ -1,321 +0,0 @@
-=================
-Queue sysfs files
-=================
-
-This text file will detail the queue files that are located in the sysfs tree
-for each block device. Note that stacked devices typically do not export
-any settings, since their queue merely functions as a remapping target.
-These files are the ones found in the /sys/block/xxx/queue/ directory.
-
-Files denoted with a RO postfix are readonly and the RW postfix means
-read-write.
-
-add_random (RW)
----------------
-This file allows to turn off the disk entropy contribution. Default
-value of this file is '1'(on).
-
-chunk_sectors (RO)
-------------------
-This has different meaning depending on the type of the block device.
-For a RAID device (dm-raid), chunk_sectors indicates the size in 512B sectors
-of the RAID volume stripe segment. For a zoned block device, either host-aware
-or host-managed, chunk_sectors indicates the size in 512B sectors of the zones
-of the device, with the eventual exception of the last zone of the device which
-may be smaller.
-
-dax (RO)
---------
-This file indicates whether the device supports Direct Access (DAX),
-used by CPU-addressable storage to bypass the pagecache.  It shows '1'
-if true, '0' if not.
-
-discard_granularity (RO)
-------------------------
-This shows the size of internal allocation of the device in bytes, if
-reported by the device. A value of '0' means device does not support
-the discard functionality.
-
-discard_max_hw_bytes (RO)
--------------------------
-Devices that support discard functionality may have internal limits on
-the number of bytes that can be trimmed or unmapped in a single operation.
-The `discard_max_hw_bytes` parameter is set by the device driver to the
-maximum number of bytes that can be discarded in a single operation.
-Discard requests issued to the device must not exceed this limit.
-A `discard_max_hw_bytes` value of 0 means that the device does not support
-discard functionality.
-
-discard_max_bytes (RW)
-----------------------
-While discard_max_hw_bytes is the hardware limit for the device, this
-setting is the software limit. Some devices exhibit large latencies when
-large discards are issued, setting this value lower will make Linux issue
-smaller discards and potentially help reduce latencies induced by large
-discard operations.
-
-discard_zeroes_data (RO)
-------------------------
-Obsolete. Always zero.
-
-fua (RO)
---------
-Whether or not the block driver supports the FUA flag for write requests.
-FUA stands for Force Unit Access. If the FUA flag is set that means that
-write requests must bypass the volatile cache of the storage device.
-
-hw_sector_size (RO)
--------------------
-This is the hardware sector size of the device, in bytes.
-
-io_poll (RW)
-------------
-When read, this file shows whether polling is enabled (1) or disabled
-(0).  Writing '0' to this file will disable polling for this device.
-Writing any non-zero value will enable this feature.
-
-io_poll_delay (RW)
-------------------
-If polling is enabled, this controls what kind of polling will be
-performed. It defaults to -1, which is classic polling. In this mode,
-the CPU will repeatedly ask for completions without giving up any time.
-If set to 0, a hybrid polling mode is used, where the kernel will attempt
-to make an educated guess at when the IO will complete. Based on this
-guess, the kernel will put the process issuing IO to sleep for an amount
-of time, before entering a classic poll loop. This mode might be a
-little slower than pure classic polling, but it will be more efficient.
-If set to a value larger than 0, the kernel will put the process issuing
-IO to sleep for this amount of microseconds before entering classic
-polling.
-
-io_timeout (RW)
----------------
-io_timeout is the request timeout in milliseconds. If a request does not
-complete in this time then the block driver timeout handler is invoked.
-That timeout handler can decide to retry the request, to fail it or to start
-a device recovery strategy.
-
-iostats (RW)
--------------
-This file is used to control (on/off) the iostats accounting of the
-disk.
-
-logical_block_size (RO)
------------------------
-This is the logical block size of the device, in bytes.
-
-max_discard_segments (RO)
--------------------------
-The maximum number of DMA scatter/gather entries in a discard request.
-
-max_hw_sectors_kb (RO)
-----------------------
-This is the maximum number of kilobytes supported in a single data transfer.
-
-max_integrity_segments (RO)
----------------------------
-Maximum number of elements in a DMA scatter/gather list with integrity
-data that will be submitted by the block layer core to the associated
-block driver.
-
-max_active_zones (RO)
----------------------
-For zoned block devices (zoned attribute indicating "host-managed" or
-"host-aware"), the sum of zones belonging to any of the zone states:
-EXPLICIT OPEN, IMPLICIT OPEN or CLOSED, is limited by this value.
-If this value is 0, there is no limit.
-
-If the host attempts to exceed this limit, the driver should report this error
-with BLK_STS_ZONE_ACTIVE_RESOURCE, which user space may see as the EOVERFLOW
-errno.
-
-max_open_zones (RO)
--------------------
-For zoned block devices (zoned attribute indicating "host-managed" or
-"host-aware"), the sum of zones belonging to any of the zone states:
-EXPLICIT OPEN or IMPLICIT OPEN, is limited by this value.
-If this value is 0, there is no limit.
-
-If the host attempts to exceed this limit, the driver should report this error
-with BLK_STS_ZONE_OPEN_RESOURCE, which user space may see as the ETOOMANYREFS
-errno.
-
-max_sectors_kb (RW)
--------------------
-This is the maximum number of kilobytes that the block layer will allow
-for a filesystem request. Must be smaller than or equal to the maximum
-size allowed by the hardware.
-
-max_segments (RO)
------------------
-Maximum number of elements in a DMA scatter/gather list that is submitted
-to the associated block driver.
-
-max_segment_size (RO)
----------------------
-Maximum size in bytes of a single element in a DMA scatter/gather list.
-
-minimum_io_size (RO)
---------------------
-This is the smallest preferred IO size reported by the device.
-
-nomerges (RW)
--------------
-This enables the user to disable the lookup logic involved with IO
-merging requests in the block layer. By default (0) all merges are
-enabled. When set to 1 only simple one-hit merges will be tried. When
-set to 2 no merge algorithms will be tried (including one-hit or more
-complex tree/hash lookups).
-
-nr_requests (RW)
-----------------
-This controls how many requests may be allocated in the block layer for
-read or write requests. Note that the total allocated number may be twice
-this amount, since it applies only to reads or writes (not the accumulated
-sum).
-
-To avoid priority inversion through request starvation, a request
-queue maintains a separate request pool per each cgroup when
-CONFIG_BLK_CGROUP is enabled, and this parameter applies to each such
-per-block-cgroup request pool.  IOW, if there are N block cgroups,
-each request queue may have up to N request pools, each independently
-regulated by nr_requests.
-
-nr_zones (RO)
--------------
-For zoned block devices (zoned attribute indicating "host-managed" or
-"host-aware"), this indicates the total number of zones of the device.
-This is always 0 for regular block devices.
-
-optimal_io_size (RO)
---------------------
-This is the optimal IO size reported by the device.
-
-physical_block_size (RO)
-------------------------
-This is the physical block size of device, in bytes.
-
-read_ahead_kb (RW)
-------------------
-Maximum number of kilobytes to read-ahead for filesystems on this block
-device.
-
-rotational (RW)
----------------
-This file is used to stat if the device is of rotational type or
-non-rotational type.
-
-rq_affinity (RW)
-----------------
-If this option is '1', the block layer will migrate request completions to the
-cpu "group" that originally submitted the request. For some workloads this
-provides a significant reduction in CPU cycles due to caching effects.
-
-For storage configurations that need to maximize distribution of completion
-processing setting this option to '2' forces the completion to run on the
-requesting cpu (bypassing the "group" aggregation logic).
-
-scheduler (RW)
---------------
-When read, this file will display the current and available IO schedulers
-for this block device. The currently active IO scheduler will be enclosed
-in [] brackets. Writing an IO scheduler name to this file will switch
-control of this block device to that new IO scheduler. Note that writing
-an IO scheduler name to this file will attempt to load that IO scheduler
-module, if it isn't already present in the system.
-
-write_cache (RW)
-----------------
-When read, this file will display whether the device has write back
-caching enabled or not. It will return "write back" for the former
-case, and "write through" for the latter. Writing to this file can
-change the kernels view of the device, but it doesn't alter the
-device state. This means that it might not be safe to toggle the
-setting from "write back" to "write through", since that will also
-eliminate cache flushes issued by the kernel.
-
-write_same_max_bytes (RO)
--------------------------
-This is the number of bytes the device can write in a single write-same
-command.  A value of '0' means write-same is not supported by this
-device.
-
-wbt_lat_usec (RW)
------------------
-If the device is registered for writeback throttling, then this file shows
-the target minimum read latency. If this latency is exceeded in a given
-window of time (see wb_window_usec), then the writeback throttling will start
-scaling back writes. Writing a value of '0' to this file disables the
-feature. Writing a value of '-1' to this file resets the value to the
-default setting.
-
-throttle_sample_time (RW)
--------------------------
-This is the time window that blk-throttle samples data, in millisecond.
-blk-throttle makes decision based on the samplings. Lower time means cgroups
-have more smooth throughput, but higher CPU overhead. This exists only when
-CONFIG_BLK_DEV_THROTTLING_LOW is enabled.
-
-write_zeroes_max_bytes (RO)
----------------------------
-For block drivers that support REQ_OP_WRITE_ZEROES, the maximum number of
-bytes that can be zeroed at once. The value 0 means that REQ_OP_WRITE_ZEROES
-is not supported.
-
-zone_append_max_bytes (RO)
---------------------------
-This is the maximum number of bytes that can be written to a sequential
-zone of a zoned block device using a zone append write operation
-(REQ_OP_ZONE_APPEND). This value is always 0 for regular block devices.
-
-zoned (RO)
-----------
-This indicates if the device is a zoned block device and the zone model of the
-device if it is indeed zoned. The possible values indicated by zoned are
-"none" for regular block devices and "host-aware" or "host-managed" for zoned
-block devices. The characteristics of host-aware and host-managed zoned block
-devices are described in the ZBC (Zoned Block Commands) and ZAC
-(Zoned Device ATA Command Set) standards. These standards also define the
-"drive-managed" zone model. However, since drive-managed zoned block devices
-do not support zone commands, they will be treated as regular block devices
-and zoned will report "none".
-
-zone_write_granularity (RO)
----------------------------
-This indicates the alignment constraint, in bytes, for write operations in
-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
-- 
2.34.1

[PATCH v2 8/8] MAINTAINERS: add entries for block layer documentation

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Include Documentation/block/ and Documentation/ABI/stable/sysfs-block in
the "BLOCK LAYER" maintainers file entry.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 MAINTAINERS | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 360e9aa0205d6..19db69dda15af 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3380,6 +3380,8 @@ M:	Jens Axboe <axboe@kernel.dk>
 L:	linux-block@vger.kernel.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git
+F:	Documentation/ABI/stable/sysfs-block
+F:	Documentation/block/
 F:	block/
 F:	drivers/block/
 F:	include/linux/blk*
-- 
2.34.1

Re: [PATCH v2 0/8] docs: consolidate sysfs-block into Documentation/ABI/

[Martin K. Petersen]

Eric,

> This series consolidates the documentation for /sys/block/<disk>/queue/
> into Documentation/ABI/, where it is supposed to go (as per Greg KH:
> https://lore.kernel.org/r/YaXXpEAwVGTLjp1e@kroah.com).
>
> This series also updates MAINTAINERS to associate the block
> documentation with the block layer.

Looks good to me. Glad to see these entries moved out of "testing".

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: [PATCH v2 0/8] docs: consolidate sysfs-block into Documentation/ABI/

[Bart Van Assche]

On 12/7/21 4:56 PM, Eric Biggers wrote:
> This series consolidates the documentation for /sys/block/<disk>/queue/
> into Documentation/ABI/, where it is supposed to go (as per Greg KH:
> https://lore.kernel.org/r/YaXXpEAwVGTLjp1e@kroah.com).
> 
> This series also updates MAINTAINERS to associate the block
> documentation with the block layer.

Thank you for having done this work! Once my two comments are addressed,
feel free to add the following to all patches in this series:

Reviewed-by: Bart Van Assche <bvanassche@acm.org>