On 2022/09/10 14:27, 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> > --- > docs/devel/zoned-storage.rst | 41 ++++++++++++++++++++++++++ > docs/system/qemu-block-drivers.rst.inc | 6 ++++ > 2 files changed, 47 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..ead2d149cc > --- /dev/null > +++ b/docs/devel/zoned-storage.rst > @@ -0,0 +1,41 @@ > +============= > +zoned-storage > +============= > + > +Zoned Block Devices (ZBDs) devide the LBA space into block regions called > zones > +that are larger than the LBA size. It can only allow sequential writes, which
s/It/They > +reduces write amplification in SSDs, leading to higher throughput and > increased > +capacity. More details about ZBDs can be found at: I would rephrase this like this, to be less assertive about the potential benefits (as they depend on the vendor implementation): ..., which can reduce write amplification in SSDs, and potentially lead to higher throughput and increased device capacity. > + > +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. > +- BLK_Z_HA: It deals with both sequential writes and random writes access. > +- BLK_Z_NONE: Regular block devices and drive-managed ZBDs are treated as > +non-zoned devices. > + > +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, the command line for zone report testing a null_blk device of > +qemu-io-cmds.c is: > +$ path/to/qemu-io --image-opts 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 > ^^^^^^^ > -- Damien Le Moal Western Digital Research
