Oleksandr Grytsov writes ("Re: [PATCH v1 1/2] libxl: introduce new backend type
VINPUT"):
> 1. Move QEMU_BACKEND macro to libxl__device_type structure as function
> and let the device to decide it has QEMU backend:
>
> struct libxl__device_type {
> ...
> device_qemu_backend_fn_t qemu_backend
> }
>
> In this case, introducing new device type for VKBD is not needed. The VKBD
> device will check backend type XS entry to define which backend is running.
Sorry for the delay replying. In your earlier mails I had trouble
figuring out what you meant but this little vignette makes it clear to
me.
I think the problem you are trying to solve is this: in your case
QEMU_BACKEND needs to depend on the visible vkb_backend field, but the
device->backend_kind is set unconditionally to just VKB ?
Could you solve this problem by inventing a new backend_kind, and
writing your own function libxl__device_from_vkb, and putting
*different* values into backend_kind ? I think that is what
backend_kind is for. See for example various console functions and
also libxl__device_from_disk.
> 2. Use string type for VKBD backend_type field instead of enum. It will be
> empty for QEMU and generic for "user space" backends.
This seems worse.
> On Mon, Oct 28, 2019 at 4:06 PM Oleksandr Grytsov <al1...@gmail.com> wrote:
> > On Wed, Oct 16, 2019 at 4:26 PM Oleksandr Grytsov <al1...@gmail.com> wrote:
> > > [Ian:]
> > > > [Oleksandr:]
> > > > > [Ian:]
> > > > > > I also don't understand why the "user space" kbd backend seems to be
> > > > > > "linux" in the enum.
> > > > >
> > > > > I agree this is not so good name. But I don't know how to call
> > > > > backends which are not running
> > > > > inside QEMU in general.
> > > >
> > > > I think this would be useable on freebsd ? "linux" definitely seems
> > > > wrong. I see it hasn't been in a release so it is not too late to
> > > > rename it, subject to discussion with Juergen as RM.
...
> > > > Maybe "linux" should be "troops"...
> > >
> > > It doesn't look as generic solution. If some user implements own backend
> > > it should add new entry into backend type enum.
Would you be prepared to change it to *something* else ?
AFAICT from the code it just uses what would the `usual' xenstore pv
control plane path for a device called "vkb" ?
So maybe we could call it "pv" ? Is there a protocol doc I should be
looking at that defines this vkb interface ?
Sorry still to be so confused.
Regards,
Ian.
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