Re: [PATCH v15 8/8] docs/zoned-storage: add zoned device documentation

[Sam Li]

Stefan Hajnoczi <stefanha@gmail.com> 于2023年2月6日周一 20:16写道：
>
> On Sun, 29 Jan 2023 at 05:31, Sam Li <faithilikerun@gmail.com> wrote:
> >
> > 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>
> > Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> > Reviewed-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
> > ---
> >  docs/devel/zoned-storage.rst           | 43 ++++++++++++++++++++++++++
> >  docs/system/qemu-block-drivers.rst.inc |  6 ++++
> >  2 files changed, 49 insertions(+)
> >  create mode 100644 docs/devel/zoned-storage.rst
>
> This patch uses the old "zoned_host_device" BlockDriver name. Please
> update it to "host_device".
>
> It's probably a good idea to search the patches for zoned_host_device
> to find any other places that need to be updated. That can be done
> with git log -p master.. | grep zoned_host_device.

Sorry for missing that. Will do.

>
> > diff --git a/docs/devel/zoned-storage.rst b/docs/devel/zoned-storage.rst
> > new file mode 100644
> > index 0000000000..03e52efe2e
> > --- /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=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
> >  ^^^^^^^
> >
> > --
> > 2.38.1
> >
> >