On Sun, 2022-10-16 at 22:51 +0800, Sam Li wrote: > Add the documentation about the zoned device support to virtio-blk > emulation. > > Signed-off-by: Sam Li <faithilike...@gmail.com> > Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com> > Reviewed-by: Damien Le Moal <damien.lem...@opensource.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 > > diff --git a/docs/devel/zoned-storage.rst b/docs/devel/zoned-storage.rst > new file mode 100644 > index 0000000000..cf169d029b > --- /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 has three zoned storage model:
replace it with +QEMU block layer supports three zoned storage models: ? with this nit, Reviewed-by: Dmitry Fomichev <dmitry.fomic...@wdc.com> > +- 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 > ^^^^^^^ >
