From: Sam Li <faithilikerun@xxxxxxxxx>
Add the documentation about the zoned device support to virtio-blk
emulation.
Signed-off-by: Sam Li <faithilikerun@xxxxxxxxx>
Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
Reviewed-by: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Dmitry Fomichev <dmitry.fomichev@xxxxxxx>
Acked-by: Kevin Wolf <kwolf@xxxxxxxxxx>
Message-id: 20230324090605.28361-9-faithilikerun@xxxxxxxxx
[Add index-api.rst to fix "zoned-storage.rst:document isn't included in
any toctree" error.
--Stefan]
Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
---
docs/devel/index-api.rst | 1 +
docs/devel/zoned-storage.rst | 43 ++++++++++++++++++++++++++
docs/system/qemu-block-drivers.rst.inc | 6 ++++
3 files changed, 50 insertions(+)
create mode 100644 docs/devel/zoned-storage.rst
diff --git a/docs/devel/index-api.rst b/docs/devel/index-api.rst
index 60c0d7459d..7108821746 100644
--- a/docs/devel/index-api.rst
+++ b/docs/devel/index-api.rst
@@ -12,3 +12,4 @@ generated from in-code annotations to function prototypes.
memory
modules
ui
+ zoned-storage
diff --git a/docs/devel/zoned-storage.rst b/docs/devel/zoned-storage.rst
new file mode 100644
index 0000000000..6a36133e51
--- /dev/null
+++ b/docs/devel/zoned-storage.rst
@@ -0,0 +1,43 @@
+=============
+zoned-storage
+=============
+
+Zoned Block Devices (ZBDs) divide 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 supports three zoned storage models:
+- BLK_Z_HM: The host-managed zoned model only allows sequential writes access
+to zones. It supports ZBD-specific I/O commands that can be used by a host to
+manage the zones of a device.
+- BLK_Z_HA: The host-aware zoned model allows random write operations in
+zones, making it backward compatible with regular block devices.
+- BLK_Z_NONE: The non-zoned model has no zones support. It includes both
+regular and drive-managed ZBD devices. ZBD-specific I/O commands are not
+supported.
+
+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=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..105cb9679c 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 host_device,
+ node-name=drive0,filename=/dev/nullb0,cache.direct=on`` to pass through
+ ``/dev/nullb0`` as ``drive0``.
+
Windows
^^^^^^^
--
2.39.2
