Re: [Xen-devel] Json config and stubdomain

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Sat, Sep 24, 2016 at 12:42:45PM +0200, Marek Marczykowski-Górecki wrote:
> Hi,
> 
> Debugging stubdomain continuation...
> When stubdomain is started, it has no json config created. This results
> in multiple problems:
>  - impossible to dynamically attach additional devices
>  - starting a domain with more than one PCI device fails
> 
> The second one is especially interesting because it look so much
> inconsistent: libxl__device_pci_add_xenstore when called for the first
> device, it immediately calls libxl__create_pci_backend and do not touch
> json config at all. But when called for the next device, it loads json
> config, adds the device there and save it. So it looks like the first
> PCI device will never be saved into json config (when added
> dynamically).
> In case of stubdomain, libxl__device_pci_add_xenstore is called during
> stubdomain startup, so defining two or more PCI devices means domain
> startup fail.

Please see  libxl_internal.h, around line 2564. The same logic is used
across all devices.

I think there could be bugs in pci device handling code. I didn't get to
test that because my test box was not capable and the code for pci
device was (and still is) rather irregular compared to other devices.

> 
> So, the question is, whether json config should be created and properly
> maintained for stubdomain, or not created at all (assuming all the
> configuration is already handled in the target domain json config)?

Stubdom configuration should be derived. It is considered internal
details.

Wei.

> 
> -- 
> Best Regards,
> Marek Marczykowski-Górecki
> Invisible Things Lab
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?



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