On Mon, Jan 28, 2019 at 17:55:14 +0100, Markus Armbruster wrote:
> Kevin Wolf <kwolf@redhat.com> writes:
> 
> > Am 28.01.2019 um 09:50 hat Peter Krempa geschrieben:
> [...]
> >> 2) Is actually using 'scsi-cd'/'scsi-hd' the better option than
> >> 'scsi-disk'?
> >
> > Yes, scsi-disk is a legacy device. Maybe we should formally deprecate
> > it.
> 
> There's an internal use in scsi_bus_legacy_add_drive(), which in turn
> powers two legacy features:
> 
> 1. -drive if=scsi
> 
>    Creates scsi-disk frontends.
> 
>    Only works with onboard HBAs since commit 14545097267, v2.12.0.
> 
> 2. -device usb-storage
> 
>    Bad magic: usb-storage pretends to be a block device, but it's really
>    a SCSI bus that can serve only a single device, which it creates
>    automatically.
> 
> If we deprecate scsi-disk, we should deprecate these, too.  Can't say
> whether that's practical right now.

Unfortunately we did not bother replacing usb-storage yet.

scsi-disk was unused for some time (if scsi-hd was supported). I just
deleted any mentions of it from libvirt now.

> 
> >> 3) Since upstream libvirt supports qemu-1.5 and newer and 'scsi-cd' is
> >> already supported there, can we assume that all newer versions support
> >> it? (Basically the question is whether it can be compiled out by
> >> upstream means).
> >
> > I think so.
> 
> Compiling out scsi-hd or scsi-cd, but not scsi-disk would be silly.  All
> three devices are in scsi-disk.c.  You'd have to hack that up to be
> silly.

That would be a downstream modification of qemu thus libvirt will
not want to support that.