Documentation: Document the new zoned loop block device driver (9e4f11c1) · Commits · git / linux-net

Documentation/admin-guide/blockdev/index.rst

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		@@ -11,6 +11,7 @@ Block Devices
		nbd
		paride
		ramdisk
		zoned_loop
		zram

		drbd/index

Documentation/admin-guide/blockdev/zoned_loop.rst

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		.. SPDX-License-Identifier: GPL-2.0

		=======================
		Zoned Loop Block Device
		=======================

		.. Contents:

		1) Overview
		2) Creating a Zoned Device
		3) Deleting a Zoned Device
		4) Example


		1) Overview
		-----------

		The zoned loop block device driver (zloop) allows a user to create a zoned block
		device using one regular file per zone as backing storage. This driver does not
		directly control any hardware and uses read, write and truncate operations to
		regular files of a file system to emulate a zoned block device.

		Using zloop, zoned block devices with a configurable capacity, zone size and
		number of conventional zones can be created. The storage for each zone of the
		device is implemented using a regular file with a maximum size equal to the zone
		size. The size of a file backing a conventional zone is always equal to the zone
		size. The size of a file backing a sequential zone indicates the amount of data
		sequentially written to the file, that is, the size of the file directly
		indicates the position of the write pointer of the zone.

		When resetting a sequential zone, its backing file size is truncated to zero.
		Conversely, for a zone finish operation, the backing file is truncated to the
		zone size. With this, the maximum capacity of a zloop zoned block device created
		can be larger configured to be larger than the storage space available on the
		backing file system. Of course, for such configuration, writing more data than
		the storage space available on the backing file system will result in write
		errors.

		The zoned loop block device driver implements a complete zone transition state
		machine. That is, zones can be empty, implicitly opened, explicitly opened,
		closed or full. The current implementation does not support any limits on the
		maximum number of open and active zones.

		No user tools are necessary to create and delete zloop devices.

		2) Creating a Zoned Device
		--------------------------

		Once the zloop module is loaded (or if zloop is compiled in the kernel), the
		character device file /dev/zloop-control can be used to add a zloop device.
		This is done by writing an "add" command directly to the /dev/zloop-control
		device::

		$ modprobe zloop
		$ ls -l /dev/zloop*
		crw-------. 1 root root 10, 123 Jan 6 19:18 /dev/zloop-control

		$ mkdir -p <base directory/<device ID>
		$ echo "add [options]" > /dev/zloop-control

		The options available for the add command can be listed by reading the
		/dev/zloop-control device::

		$ cat /dev/zloop-control
		add id=%d,capacity_mb=%u,zone_size_mb=%u,zone_capacity_mb=%u,conv_zones=%u,base_dir=%s,nr_queues=%u,queue_depth=%u,buffered_io
		remove id=%d

		In more details, the options that can be used with the "add" command are as
		follows.

		================ ===========================================================
		id Device number (the X in /dev/zloopX).
		Default: automatically assigned.
		capacity_mb Device total capacity in MiB. This is always rounded up to
		the nearest higher multiple of the zone size.
		Default: 16384 MiB (16 GiB).
		zone_size_mb Device zone size in MiB. Default: 256 MiB.
		zone_capacity_mb Device zone capacity (must always be equal to or lower than
		the zone size. Default: zone size.
		conv_zones Total number of conventioanl zones starting from sector 0.
		Default: 8.
		base_dir Path to the base directoy where to create the directory
		containing the zone files of the device.
		Default=/var/local/zloop.
		The device directory containing the zone files is always
		named with the device ID. E.g. the default zone file
		directory for /dev/zloop0 is /var/local/zloop/0.
		nr_queues Number of I/O queues of the zoned block device. This value is
		always capped by the number of online CPUs
		Default: 1
		queue_depth Maximum I/O queue depth per I/O queue.
		Default: 64
		buffered_io Do buffered IOs instead of direct IOs (default: false)
		================ ===========================================================

		3) Deleting a Zoned Device
		--------------------------

		Deleting an unused zoned loop block device is done by issuing the "remove"
		command to /dev/zloop-control, specifying the ID of the device to remove::

		$ echo "remove id=X" > /dev/zloop-control

		The remove command does not have any option.

		A zoned device that was removed can be re-added again without any change to the
		state of the device zones: the device zones are restored to their last state
		before the device was removed. Adding again a zoned device after it was removed
		must always be done using the same configuration as when the device was first
		added. If a zone configuration change is detected, an error will be returned and
		the zoned device will not be created.

		To fully delete a zoned device, after executing the remove operation, the device
		base directory containing the backing files of the device zones must be deleted.

		4) Example
		----------

		The following sequence of commands creates a 2GB zoned device with zones of 64
		MB and a zone capacity of 63 MB::

		$ modprobe zloop
		$ mkdir -p /var/local/zloop/0
		$ echo "add capacity_mb=2048,zone_size_mb=64,zone_capacity=63MB" > /dev/zloop-control

		For the device created (/dev/zloop0), the zone backing files are all created
		under the default base directory (/var/local/zloop)::

		$ ls -l /var/local/zloop/0
		total 0
		-rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000000
		-rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000001
		-rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000002
		-rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000003
		-rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000004
		-rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000005
		-rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000006
		-rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000007
		-rw-------. 1 root root 0 Jan 6 22:23 seq-000008
		-rw-------. 1 root root 0 Jan 6 22:23 seq-000009
		...

		The zoned device created (/dev/zloop0) can then be used normally::

		$ lsblk -z
		NAME ZONED ZONE-SZ ZONE-NR ZONE-AMAX ZONE-OMAX ZONE-APP ZONE-WGRAN
		zloop0 host-managed 64M 32 0 0 1M 4K
		$ blkzone report /dev/zloop0
		start: 0x000000000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)]
		start: 0x000020000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)]
		start: 0x000040000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)]
		start: 0x000060000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)]
		start: 0x000080000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)]
		start: 0x0000a0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)]
		start: 0x0000c0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)]
		start: 0x0000e0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)]
		start: 0x000100000, len 0x020000, cap 0x01f800, wptr 0x000000 reset:0 non-seq:0, zcond: 1(em) [type: 2(SEQ_WRITE_REQUIRED)]
		start: 0x000120000, len 0x020000, cap 0x01f800, wptr 0x000000 reset:0 non-seq:0, zcond: 1(em) [type: 2(SEQ_WRITE_REQUIRED)]
		...

		Deleting this device is done using the command::

		$ echo "remove id=0" > /dev/zloop-control

		The removed device can be re-added again using the same "add" command as when
		the device was first created. To fully delete a zoned device, its backing files
		should also be deleted after executing the remove command::

		$ rm -r /var/local/zloop/0

MAINTAINERS

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		@@ -26728,6 +26728,7 @@ M: Damien Le Moal <dlemoal@kernel.org>
		R: Christoph Hellwig <hch@lst.de>
		L: linux-block@vger.kernel.org
		S: Maintained
		F: Documentation/admin-guide/blockdev/zoned_loop.rst
		F: drivers/block/zloop.c

		ZONEFS FILESYSTEM

drivers/block/Kconfig

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		@@ -421,6 +421,9 @@ config BLK_DEV_ZONED_LOOP
		echo "add id=0,zone_size_mb=256,capacity_mb=16384,conv_zones=11" > \
		/dev/zloop-control

		See Documentation/admin-guide/blockdev/zoned_loop.rst for usage
		details.

		If unsure, say N.

		endif # BLK_DEV