Re: [PATCH v3 03/11] vpci/header: Move register assignments from init_bars

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Oct 27, 2021 at 11:59:47AM +0000, Oleksandr Andrushchenko wrote:
> Hi, Roger!
> 
> On 27.10.21 13:17, Oleksandr Andrushchenko wrote:
> > Hi, Roger!
> >
> > On 13.10.21 16:51, Roger Pau Monné wrote:
> >> On Thu, Sep 30, 2021 at 10:52:15AM +0300, Oleksandr Andrushchenko wrote:
> >>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> >>>
> >>> This is in preparation for dynamic assignment of the vPCI register
> >>> handlers depending on the domain: hwdom or guest.
> >>> The need for this step is that it is easier to have all related 
> >>> functionality
> >>> put at one place. When the subsequent patches add decisions on which
> >>> handlers to install, e.g. hwdom or guest handlers, then this is easily
> >>> achievable.
> >> Won't it be possible to select the handlers to install in init_bars
> >> itself?
> > It is possible
> >> Splitting it like that means you need to iterate over the numbers of
> >> BARs twice (one in add_bar_handlers and one in init_bars), which makes
> >> it more likely to introduce errors or divergences.
> >>
> >> Decoupling the filling of vpci_bar data with setting the handlers
> >> seems slightly confusing.
> > Ok, I won't introduce add_bar_handlers, thus rendering this patch useless.
> > I'll drop it and re-work the upcoming patches with this respect
> On the other hand after thinking a bit more.
> What actually init_bars do?
> 1. Runs once per each pdev (__init?)
> 2. Sizes the BARs and detects their type, sets up pdev->vpci->header BAR 
> values
> 3. Adds register handlers.
> 
> For DomU we only need 3), so we can setup guest handlers.

I think you assume that there will always be a hardware domain with
vPCI enabled that will get the device assigned and thus init_bars will
be executed prior to assigning to a domU.

But what about dom0less, or when using a classic PV dom0? In that case
the device won't get assigned to a hardware domain with vPCI support,
so the vpci structure won't be allocated or filled, and hence
init_bars would have to be executed when assigning to a domU.

Thanks, Roger.