Re: [PATCH 1/6] virtio-scsi.h: Add virtio_scsi_cmd_req_pi + VIRTIO_SCSI_F_T10_PI bits

[Paolo Bonzini <pbonzini@redhat.com>]

Il 07/04/2014 05:55, Michael S. Tsirkin ha scritto:
>> > +	u16 do_pi_niov;		/* DataOUT PI Number of iovecs */
>> > +	u16 di_pi_niov;		/* DataIN PI Number of iovecs */
> So this looks like a somewhat problematic interface to me in that
> it talks in terms of iovecs not bytes.
> So this perpetuates the assumption that header is in a separate
> iov from data (and protection is separate from data).
> Arguably virtio doesn't work in terms of iovecs on the guest side so
> this naming looks strange.
> Further host side, get_vq_descs can in theory split a buffer to multiple
> iovecs if it crosses the boundary of a memory region.
>
> One solution is to use byte lengths here, but this does require
> that vhost scsi gets rid of layout assumptions generally.
> Not sure that's practical for -rc1.

Why does that require that vhost scsi gets rid of layout assumptions?

The interface uses bytes instead of iovecs as the unit, and vhost-scsi 
can add the (temporary...) requirement that do_pi_nbytes and 
di_pi_nbytes comprise an integer number of iovecs.

Paolo