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[PATCH v11 7/7] docs/zoned-storage: add zoned device documentation
From: |
Sam Li |
Subject: |
[PATCH v11 7/7] docs/zoned-storage: add zoned device documentation |
Date: |
Mon, 10 Oct 2022 10:21:16 +0800 |
Add the documentation about the zoned device support to virtio-blk
emulation.
Signed-off-by: Sam Li <faithilikerun@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
docs/devel/zoned-storage.rst | 40 ++++++++++++++++++++++++++
docs/system/qemu-block-drivers.rst.inc | 6 ++++
2 files changed, 46 insertions(+)
create mode 100644 docs/devel/zoned-storage.rst
diff --git a/docs/devel/zoned-storage.rst b/docs/devel/zoned-storage.rst
new file mode 100644
index 0000000000..deaa4ce99b
--- /dev/null
+++ b/docs/devel/zoned-storage.rst
@@ -0,0 +1,40 @@
+=============
+zoned-storage
+=============
+
+Zoned Block Devices (ZBDs) devide the LBA space into block regions called zones
+that are larger than the LBA size. They can only allow sequential writes, which
+can reduce write amplification in SSDs, and potentially lead to higher
+throughput and increased capacity. More details about ZBDs can be found at:
+
+https://zonedstorage.io/docs/introduction/zoned-storage
+
+1. Block layer APIs for zoned storage
+-------------------------------------
+QEMU block layer has three zoned storage model:
+- BLK_Z_HM: This model only allows sequential writes access. It supports a set
+of ZBD-specific I/O request that used by the host to manage device zones.
+- BLK_Z_HA: It deals with both sequential writes and random writes access.
+- BLK_Z_NONE: Regular block devices and drive-managed ZBDs are treated as
+non-zoned devices.
+
+The block device information resides inside BlockDriverState. QEMU uses
+BlockLimits struct(BlockDriverState::bl) that is continuously accessed by the
+block layer while processing I/O requests. A BlockBackend has a root pointer to
+a BlockDriverState graph(for example, raw format on top of file-posix). The
+zoned storage information can be propagated from the leaf BlockDriverState all
+the way up to the BlockBackend. If the zoned storage model in file-posix is
+set to BLK_Z_HM, then block drivers will declare support for zoned host device.
+
+The block layer APIs support commands needed for zoned storage devices,
+including report zones, four zone operations, and zone append.
+
+2. Emulating zoned storage controllers
+--------------------------------------
+When the BlockBackend's BlockLimits model reports a zoned storage device, users
+like the virtio-blk emulation or the qemu-io-cmds.c utility can use block layer
+APIs for zoned storage emulation or testing.
+
+For example, to test zone_report on a null_blk device using qemu-io is:
+$ path/to/qemu-io --image-opts -n driver=zoned_host_device,filename=/dev/nullb0
+-c "zrp offset nr_zones"
diff --git a/docs/system/qemu-block-drivers.rst.inc
b/docs/system/qemu-block-drivers.rst.inc
index dfe5d2293d..0b97227fd9 100644
--- a/docs/system/qemu-block-drivers.rst.inc
+++ b/docs/system/qemu-block-drivers.rst.inc
@@ -430,6 +430,12 @@ Hard disks
you may corrupt your host data (use the ``-snapshot`` command
line option or modify the device permissions accordingly).
+Zoned block devices
+ Zoned block devices can be passed through to the guest if the emulated
storage
+ controller supports zoned storage. Use ``--blockdev zoned_host_device,
+ node-name=drive0,filename=/dev/nullb0`` to pass through ``/dev/nullb0``
+ as ``drive0``.
+
Windows
^^^^^^^
--
2.37.3
- [PATCH v11 3/7] block: add block layer APIs resembling Linux ZonedBlockDevice ioctls, (continued)
[PATCH v11 4/7] raw-format: add zone operations to pass through requests, Sam Li, 2022/10/09
[PATCH v11 5/7] config: add check to block layer, Sam Li, 2022/10/09
[PATCH v11 6/7] qemu-iotests: test new zone operations, Sam Li, 2022/10/09
[PATCH v11 7/7] docs/zoned-storage: add zoned device documentation,
Sam Li <=