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

From: Paolo Bonzini
Subject: Re: [Qemu-block] [PATCH 0/4] virtio: handle zoned backing devices
Date: Wed, 10 Jul 2019 12:09:07 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2

On 09/07/19 22:38, Dmitry Fomichev wrote:
> 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.

The problem with this approach is that other devices (e.g. ide-hd or sd
card) also break with zoned devices and the only way to fix it would be
to add code denying zoned block devices to all of them.

The question then becomes how to define a whitelist.  One possiblity is
to add a QOM interface (for example TYPE_ZONED_BLOCK_SUPPORT) to
scsi-block and scsi-generic.  In do_parse_drive you can query the
BlockBackend with bdrv_get_zoned_info, and return an error if the
backend is a zoned block device and the device does not implement
TYPE_ZONED_BLOCK_SUPPORT.  (Commit 6b1566c is an example of adding a new
QOM interface; in your case, it would be simpler as the interface would
not have any method).  Kevin, what do you think?

Also, why deny passing Host Aware devices?


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