Re: [Xen-devel] [PATCH] libxl: No emulated disk driver for xvdX disk

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Tue, Oct 27, 2015 at 11:11 AM, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
> On Mon, 26 Oct 2015, Boris Ostrovsky wrote:
>> On 10/16/2015 10:01 AM, Ian Jackson wrote:
>> > Anthony PERARD writes ("[PATCH] libxl: No emulated disk driver for xvdX
>> > disk"):
>> > > When a guest configuration list xvdX for its disks, there is no need to
>> > > provide an emulated driver for the same target.
>> > >
>> > > Such configuration can work with the OVMF firmware, as it supports PV
>> > > disk.
>> > Acked-by: Ian Jackson<ian.jackson@xxxxxxxxxxxxx>
>> >
>> > I have checked this with the docs, and this change makes the libxl
>> > behave as documented and as I intended when I wrote the doc.
>> >
>>
>>
>> This commit prevents a guest from seeing disks that specify xvdX ("disk = [
>> '/root/virt/fedora.img,raw,xvda,rw' ]", for example).
>>
>> TBH, I am not sure I understand how this is supposed to work --- how is the
>> guest expected to discover the disk?
>
> The guest can access xvdX disks via the PV block protocol, or via
> UEFI firmare using EFI BootServices.

But it introduces a sort of regression in some setups -- namely,
before you could use exactly the same disk and config file for either
a PV or HVM guest, simply adding builder=hvm (either to the file or
the command line) to switch between the two.

I'm not sure how many people depend on disk=[...xvda] working on
non-OVMF HVM guests, but my current testing setups certainly do.

 -George

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