Re: Interesting qemu/virt-manager bug about the "rotational" attribute on virtio-blk disks

[Stefano Garzarella]

+Cc Michael, Stefan, virtualization@lists.linux-foundation.org

On Thu, Jul 16, 2020 at 09:06:14AM +0100, Richard W.M. Jones wrote:
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1857515
> 
> A virtio-blk disk which is backed by a raw file on an SSD,
> inside the guest shows rotational = 1.
> 
> I assumed that qemu must have a "rotational" property for disks and
> this would be communicated by virtio to the guest, but qemu and virtio
> don't seem to have this.  Pretty surprising!  Is it called something
> other than "rotational"?
> 

I'm not sure if we need to add this property in QEMU, but in Linux
I found these flags (include/linux/blkdev.h) for the block queues:

    #define QUEUE_FLAG_NONROT   6       /* non-rotational device (SSD) */
    #define QUEUE_FLAG_VIRT             QUEUE_FLAG_NONROT /* paravirt device */

xen-blkfront driver is the only one that sets the QUEUE_FLAG_VIRT,
should we do the same in the virtio-blk driver regardless of the backend?

Thanks,
Stefano