Re: [Qemu-devel] [PATCH] virtio-scsi: fix "written length" field in the used ring

[Paolo Bonzini <pbonzini@redhat.com>]

On 27/04/2015 16:04, Michael S. Tsirkin wrote:
>> > Because virtio-blk uses a response footer and virtio-scsi uses a
>> > response header, fixing virtio-blk is much harder.  You need to add a
>> > new argument to virtqueue_push.  I'd really prefer someone else to do it...
>> > 
>> > Paolo
> OK but what's the desired API?
> Do you know the host length or might any part of iov
> be dirty?

For a 1-sector request and a 2048+1 bytes iov, I know that I've written
bytes 0-511 and byte 2048.

So I have to dirty all 2049 bytes, but the written length should be 512.
 Right now we pass 2049 to virtqueue_push and write 2049 to the written
length, I'd need another argument to pass the 512.

Paolo