Re: [Qemu-block] [Qemu-devel] [PULL 25/26] block: Remove deprecated -drive option serial

[Daniel P . Berrangé]

On Fri, Jun 22, 2018 at 07:54:00PM +0200, Kevin Wolf wrote:
> Am 22.06.2018 um 17:40 hat Daniel P. Berrangé geschrieben:
> > On Fri, Jun 22, 2018 at 04:25:13PM +0200, Kevin Wolf wrote:
> > > This was in fact one release longer than our deprecation policy says.
> > > Are we serious about the deprecation policy or aren't we?
> > > 
> > > I might consider reverting a change if it turned out that this requires
> > > some massive work in libvirt. But I think this one should be rather easy
> > > to fix in libvirt until 3.0 is released.
> > 
> > I've got a patch mostly ready that converts libvirt to setting these things
> > on the frontend device, however, I've got some queries...
> > 
> >  - usb-storage  - doesn't appear to support geometry or werror/rerror
> > 
> >    Will we loose functionality by stopping use of -drive for werror
> > 
> >    Loosing geometry feels relevant too, unless it was already ignored
> >    when set opf -drive ?
> 
> You're right, usb-storage doesn't allow using -device to specify these,
> and it does use the values from -drive.
> 
> For werror/rerror, we should clearly implement the option forwarding to
> scsi-disk so that you can make use of it.

This missing werror item looks like a blocker for libvirt to be
able to switch to using -blockdev without a regression.

> I'm not sure how sane specifying a non-standard CHS geometry for a USB
> stick actually is. As an additional difficulty, usb-storage internally
> creates a scsi-disk device (not scsi-hd), which is also considered
> legacy and doesn't support the geometry options either, so it's not just
> simple forwarding. We removed an actual feature there, but that feature
> was probably never intended nor used.
> 
> If someone comes up with a compelling reason why they really need to
> configure the CHS geometry of their USB sticks, I guess we can do it. My
> real USB sticks I tested don't even support MODE_PAGE_HD_GEOMETRY
> (though they have MODE_PAGE_FLEXIBLE_DISK_GEOMETRY).

I don't think libvirt has a compelling reason. The ability to set CHS
on usb-storage is just something we got for free because it used the
same -drive syntax as other disk device frontends. It would be nice to
avoid the regression but I doubt people will actually notice in practice
as usb-storage users are few & far between, and even fewer of those will
care about CHS.

Regards,
Daniel
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