Currently, attaching zoned block devices (i.e. storage devices compliant to ZAC/ZBC standards) using several virtio methods doesn't work properly as 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. The virtio-scsi-pci/scsi-block method works with a recent patch. The virtio-scsi-pci/scsi-generic method also appears to handle zoned devices without problems. This patchset adds code to check if the backing device that is being opened is a zoned Host Managed device. If this is the case, the patch prohibits virtualization of the device for all use cases lacking proper zoned support. Host Aware zoned block devices are designed to work as regular block devices at a guest system that does not support ZBD. Therefeore, this patchset doesn't prohibit attachment of Host Aware devices. Host Aware attachments were tested using file_zbc handler of tcmu-runner daemon. Running QEMU against zoned devices provisioned by tcmu-runner emulator exposed another problem - upon startup, QEMU would exit via divide by zero exception in scsi_disk_reset(). The reason for this is that tcmu-runner zoned devices don't support READ CAPACITY(10). This is by design, since only READ CAPACITY(16) support is mandatory for ZBDs and READ CAPACITY(10) is optional. The last commit of this series fixes this problem. 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 (4): block: Add zoned device model property raw: Recognize zoned backing devices block/ide/scsi: Set BLK_PERM_SUPPORT_ZONED raw: Don't open ZBDs if backend can't handle them Shin'ichiro Kawasaki (1): hw/scsi: Check sense key before READ CAPACITY output snoop block.c | 19 +++++++++ block/file-posix.c | 88 +++++++++++++++++++++++++++++++++------ block/raw-format.c | 8 ++++ hw/block/block.c | 8 +++- hw/block/fdc.c | 4 +- hw/block/nvme.c | 2 +- hw/block/virtio-blk.c | 2 +- hw/block/xen-block.c | 2 +- hw/ide/qdev.c | 2 +- hw/scsi/scsi-disk.c | 13 +++--- hw/scsi/scsi-generic.c | 33 +++++++++------ hw/usb/dev-storage.c | 2 +- include/block/block.h | 21 +++++++++- include/block/block_int.h | 4 ++ include/hw/block/block.h | 3 +- 15 files changed, 169 insertions(+), 42 deletions(-) -- 2.21.0
