Re: [PATCH v18 0/8] Add support for zoned device

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Sam,

On 24/3/23 10:05, Sam Li wrote:
> Zoned Block Devices (ZBDs) devide the LBA space to block regions called zones
> that are larger than the LBA size. It can only allow sequential writes, which
> reduces write amplification in SSD, leading to higher throughput and increased
> capacity. More details about ZBDs can be found at:
> 
> https://zonedstorage.io/docs/introduction/zoned-storage
> 
> The zoned device support aims to let guests (virtual machines) access zoned
> storage devices on the host (hypervisor) through a virtio-blk device. This
> involves extending QEMU's block layer and virtio-blk emulation code.  In its
> current status, the virtio-blk device is not aware of ZBDs but the guest sees
> host-managed drives as regular drive that will runs correctly under the most
> common write workloads.
> 
> This patch series extend the block layer APIs with the minimum set of zoned
> commands that are necessary to support zoned devices. The commands are - Report
> Zones, four zone operations and Zone Append.
> 
> There has been a debate on whethre introducing new zoned_host_device BlockDriver
> specifically for zoned devices. In the end, it's been decided to stick to
> existing host_device BlockDriver interface by only adding new zoned operations
> inside it. The benefit of that is to avoid further changes - one example is
> command line syntax - to the applications like Libvirt using QEMU zoned
> emulation.
> 
> It can be tested on a null_blk device using qemu-io or qemu-iotests. For
> example, to test zone report using qemu-io:
> $ path/to/qemu-io --image-opts -n driver=host_device,filename=/dev/nullb0
> -c "zrp offset nr_zones"

Sorry to jump late, but the patch subject prefixes are a bit confusing.
Some suggestions:

> Sam Li (8):
>    include: add zoned device structs

block/block-common: ...

>    file-posix: introduce helper functions for sysfs attributes

block/file-posix: ...

>    block: add block layer APIs resembling Linux ZonedBlockDevice ioctls

block/block-backend: ...

>    raw-format: add zone operations to pass through requests

block/raw-format: ...

>    config: add check to block layer

block: ...

>    qemu-iotests: test new zone operations

iotests: ...

>    block: add some trace events for new block layer APIs

I'd squash that with patch #4 "block/raw-format: add zone operations to 
pass through requests".

Regards,

Phil.

>    docs/zoned-storage: add zoned device documentation
> 
>   block.c                                |  19 ++
>   block/block-backend.c                  | 133 ++++++++
>   block/file-posix.c                     | 444 +++++++++++++++++++++++--
>   block/io.c                             |  41 +++
>   block/raw-format.c                     |  18 +
>   block/trace-events                     |   2 +
>   docs/devel/zoned-storage.rst           |  43 +++
>   docs/system/qemu-block-drivers.rst.inc |   6 +
>   include/block/block-common.h           |  43 +++
>   include/block/block-io.h               |   9 +
>   include/block/block_int-common.h       |  29 ++
>   include/block/raw-aio.h                |   6 +-
>   include/sysemu/block-backend-io.h      |  18 +
>   meson.build                            |   4 +
>   qemu-io-cmds.c                         | 149 +++++++++
>   tests/qemu-iotests/tests/zoned         |  89 +++++
>   tests/qemu-iotests/tests/zoned.out     |  53 +++
>   17 files changed, 1069 insertions(+), 37 deletions(-)
>   create mode 100644 docs/devel/zoned-storage.rst
>   create mode 100755 tests/qemu-iotests/tests/zoned
>   create mode 100644 tests/qemu-iotests/tests/zoned.out
>