Re: [Xen-devel] [RFC] PVFB: Add refresh period to XenStore parameters?

[Markus Armbruster <armbru@xxxxxxxxxx>]

Samuel Thibault <samuel.thibault@xxxxxxxxxxxxx> writes:

> Markus Armbruster, le Tue 06 May 2008 15:50:08 +0200, a Ãcrit :
>> > +    for (i = 0, cons = page->in_cons; cons != prod; i++, cons++) {
>> 
>> Purpose of i ?
>
> It was needed in the case of kbd, but not here indeed.
>
>> > +        int notified_active;   /* Did we request update */
>> 
>> Tab, please, if it's not too much trouble.  Mixing tabs and spaces for
>> indentation makes diffs unnecessarily hard to read.
>
> I agree and fixed it, the problem is just that xen has various
> indentation/tab practices, so no default configuration can work :)

I know...

>> > +/*
>> > + * Backend idleness report
>> > + * Backend sends it when the output window is somehow non visible
>> > + * (minimized, no client, etc.)
>> > + */
>> > +#define XENFB_TYPE_BACKEND_STATUS 1
>> > +
>> > +#define XENFB_BACKEND_STATUS_IDLE 0
>> > +#define XENFB_BACKEND_STATUS_ACTIVE 1
>> > +
>> > +struct xenfb_backend_status
>> > +{
>> > +    uint8_t type;    /* XENFB_TYPE_BACKEND_STATUS */
>> > +    uint8_t status;  /* XENFB_BACKEND_STATUS_* */
>> > +};
>> 
>> I'm not entirely happy with the protocol defined here.
>
> Right, I'm not sure of what we would ideally want to express. I can see
> three use cases:
>
> - The output is fully active, we want frequent update notification
>   (that is the assumed permanent state up to now)
> - The output is not visible, update notification is useless.
> - The output is visible in reduced conditions, for instance a thumbnail
>   in a VMs management tool, update notification don't really need to be
>   sent often.  We could have the backend explicitely request updates
>   from the frontend when it wants a new thumbnail (this is needed e.g.
>   in HVM text mode, in which the guest output is not directly mapped
>   through PVFB, so an explicit refresh is needed).
>
> Instead of expressing idleness or "status", maybe we could rather
> express whether periodic update notifications are wanted or not, and let
> the backend request an explicit update notification when it feels the
> need for one (low-frequency thumbnail update). It has the advantage of
> only talking about the PVFB protocol itself and not something around it
> (idleness of the actual output).  That is also backward compatible in
> that a frontend which doesn't know these two events will just continue
> sending periodic update notifications, which is fine for the backend.
>
> Samuel

I think that's a better way to define this feature.

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