[Qemu-devel] [PATCH 0/4] virtio: handle zoned backing devices

[Dmitry Fomichev]

Currently, attaching zoned block devices (i.e. storage devices
compliant to ZAC/ZBC standards) using several virtio methods doesn't
work - the zoned devices appear as regular block devices at the guest.
This may cause unexpected i/o errors and, potentially, some data
corruption.

To be more precise, attaching a zoned device via virtio-pci-blk,
virtio-scsi-pci/scsi-disk or virtio-scsi-pci/scsi-hd demonstrates the
above behavior. A simple fix is needed to make
virtio-scsi-pci/scsi-block work and this is covered by a different
patch. The virtio-scsi-pci/scsi-generic method appears to handle zoned
devices without problems.

This patchset adds code to check if the backing device that is being
opened is zoned. If this is the case, the new code prohibits
virtualization of the device for all use cases lacking proper zoned
support.

Considering that there is still a couple of different working ways
to virtualize a ZBD, this patchset provides a reasonable short-term
solution for this problem. What about long term?

It appears to be beneficial to add proper ZBD support to virtio-blk.
In order to support this use case properly, some virtio-blk protocol
changes will be necessary. They are needed to allow the host code to
propagate some ZBD properties that are required for virtio guest
driver to configure the guest block device as ZBD, such as zoned
device model, zone size and the total number of zones. Further, some
support needs to be added for REPORT ZONES command as well as for zone
operations, such as OPEN ZONE, CLOSE ZONE, FINISH ZONE and RESET ZONE.

These additions to the protocol are relatively straightforward, but
they need to be approved by the virtio TC and the whole process may
take some time.

ZBD support for virtio-scsi-pci/scsi-disk and virtio-scsi-pci/scsi-hd
does not seem as necessary. Users will be expected to attach zoned
block devices via virtio-scsi-pci/scsi-block instead.

This patchset contains some Linux-specific code. This code is
necessary to obtain Zoned Block Device model value from Linux sysfs.
Dmitry Fomichev (3):
  block: Add zoned device model property
  raw: Recognize zoned backing devices
  virtio-blk: Don't realize zoned block devices

Shin'ichiro Kawasaki (1):
  hw/scsi: Don't realize zoned block devices for virtio-scsi legacy
    drivers

 block.c                        | 14 +++++++
 block/block-backend.c          | 20 ++++++++++
 block/file-posix.c             | 69 ++++++++++++++++++++++++++++------
 block/raw-format.c             |  8 ++++
 hw/block/virtio-blk.c          |  5 +++
 hw/scsi/scsi-disk.c            |  5 +++
 include/block/block.h          |  9 +++++
 include/block/block_int.h      |  4 ++
 include/sysemu/block-backend.h |  2 +
 9 files changed, 125 insertions(+), 11 deletions(-)

-- 
2.21.0