Re: [Xen-devel] [PATCH 02/11] xen/arm: vpl011: Add new hvm params in Xen for ring buffer/event setup

[Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx>]

Hi Stefano,

On 12 April 2017 at 03:37, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
> On Tue, 11 Apr 2017, Bhupinder Thakur wrote:
>> Hi,
>>
>> Kindly let me know if my understanding is correct.
>>
>> Using a domctl API will allow us to keep the vUART configuration
>> flexible. Currently, we can operate on one ring-buf PFN and an event
>> channel port only for a single vUART but if we use DOMCTL interface,
>> then we can effectively get/set multiple event channel ports/multiple
>> PFNs from/to Xen in a single domctl call.
>>
>> I am not clear who will be the caller of this domctl API. Is it
>> xenconsoled or the toolstack? Currently, xenconsoled reads the
>> ring-buf PFN and event channel from the xenstore, which is populated
>> by the toolstack.
>
> The caller could be either, but I think it would make sense for it to be
> xenconsoled to cut the middle-man (xl).
>
I see the issue with Xenconsoled getting the PFN using a DOMCTL API.

PFN is allocated in alloc_magic_pages() which is part of
libxenguest.so and the DOMCTL API is part of libxenctrl.so. As per my
understanding, libxenguest.so has dependency on libxenctrl.so but not
the other way round.So I am not sure how libxenctrl can call into
libxenguest to get the PFN.

If the DOMCTL API is called from libxenguest then I can get the PFN easily.

Regards,
Bhupinder

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