Re: [Xen-devel] blktap, qdisk, xl cd-eject, and xencommons

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 04/30/2013 11:21 AM, Ian Campbell wrote:
> On Tue, 2013-04-30 at 11:02 +0100, George Dunlap wrote:
> > The second is problems with xl cd-insert and eject, initially reported
> > by Fabio Fantoni, and then (accidentally) reproduced by me.  The
> > problem turns out to be libxl using blktap for cdroms.  Basically,
> > AFAICT, the whole cd-insert cd-eject thing completely doen't work if
> > blktap is used to provide it; and it's not a simple fix.
> cd-insert/eject are suppose to operate on emulated CDROM, which blktap
> simply isn't in a position to provide, even if it was capable of doing
> so. So this is certainly wrong IMHO at some level.
>
> All emulated disks have a PV counterpart. Many (all?) PVHVM drivers
> choose not to unplug the emulated CDROM and use it in preference to the
> PV version (since this way they get proper media change events etc) but
> I don't think they are required to behave like this.
>
> In principal it's not wrong to provide the PV face of a device from a
> different backend to the emulated one (e.g. we do blkback+qdisk all the
> time for disks), but in the interests of simplicity it seems like the
> obvious thing to do is to unconditionally use qdisk for both faces of an
> HVM guest's CDROM.
Right -- so I guess from a release perspective the best thing to do 
would just be to have tools/libxl/libxl_device.c:disk_try_backend() fail 
for TAP if disk->is_cdrom is true?
 -George

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