Re: [PATCH v11 7/7] docs/zoned-storage: add zoned device documentation

[Sam Li]

Hannes Reinecke <hare@suse.de> 于2022年10月10日周一 14:19写道：
>
> On 10/10/22 04:21, Sam Li 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>
> > ---
> >   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
>
> divide
>
> > +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.
>
> Maybe:
> This model only allow for sequential write access to zones. It supports
> ZBD-specific I/O requests to manage device zones.
>
> > +- BLK_Z_HA: It deals with both sequential writes and random writes access.
>
> Maybe better:
> This model allows sequential and random writes to zones. It supports
> ZBD-specific I/O requests to manage device zones.
>
> > +- BLK_Z_NONE: Regular block devices and drive-managed ZBDs are treated as
> > +non-zoned devices.
>
> Maybe:
> This is the default model with no zones support; it includes both
> regular and drive-managed ZBD devices. ZBD-specific I/O requests are not
> supported.

Thanks!

>
> > +
> > +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
> >   ^^^^^^^
> >
>
> Cheers,
>
> Hannes
> --
> Dr. Hannes Reinecke                Kernel Storage Architect
> hare@suse.de                              +49 911 74053 688
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