Re: [PATCH 06/10 v2] xen/arm: vpl011: Add vuart ring-buf and evtchn to xenstore

From: Bhupinder Thakur <bhupinder.thakur@linaro.org>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: Wei Liu <wei.liu2@citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	Julien Grall <julien.grall@arm.com>,
	Jan Beulich <jbeulich@suse.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH 06/10 v2] xen/arm: vpl011: Add vuart ring-buf and evtchn to xenstore
Date: Wed, 3 May 2017 16:30:50 +0530	[thread overview]
Message-ID: <CACtJ1JRATrFE9es0myAYnMSOw6Ke7ug24NM3mJ3x=GBABDXiqA@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1705011046100.8859@sstabellini-ThinkPad-X260>

Hi,

>> > It looks like you are reusing the libxl__device_console_add call for the
>> > main PV console for the domain, to also add the vuart nodes to xenstore.
>> >
>> > I don't think it is a good idea to mix the two. I suggest to introduce a
>> > new libxl__device call to introduce the vuart nodes to xenstore, given
>> > that they have no relantionship with the principal PV console of the
>> > domain.
>> >
>> I have a doubt here. Do I have to create a new console device
>> (libxl__device) to register the vuart console or can I use the
>> existing console device (which is used for registering the primary
>> console) to register the vuart nodes to xenstore?
>>
>> I suspect that if I try to register with the same console device then
>> libxl__device_generic_add() may fail as it is already added.
>
> The vuart we are introducing with this patch series is a new and
> different console from the existing PV console. So yes, I think we need
> to create a new device for it.
>
> We either need to introduce a brand new function to add the vuart to
> xenstore, something like libxl__device_vuart_add, or, if we are going
> to reuse libxl__device_console_add, then we we need to create both a new
> console device (libxl__device_console), and a new libxl__device for it.
> For clarity, libxl__device_console is the input parameter of
> libxl__device_console_add, while libxl__device is the output parameter.
>
I am trying to add a new vuart device by defining a new device type
LIBXL__DEVICE_KIND_VUART  and a new function
libxl__device_vuart_add().

This function basically adds the vuart ring-ref ("0/ring-ref") and
port ("0/port") to ro_front array and then it registers the device
using the libxl__device_generic_add(). I pass NULL to "back" and
"front" array arguments to  libxl__device_generic_add() as I am adding
parameters only to "ro_front" array.

I am adding the device at /local/domain/<domid>/vuart.

However, xenconsoled fails to read the vuart ring-ref and port saying
"no such directory or file".I verified that
libxl__device_generic_add() is returning successfully.

In xenconsoled, I verified that I am reading
/local/domain/<domid>/vuart/0/ring-ref and
/local/domain/<domid>/vuart/0/port.

It is not clear why xenconsoled fails to read the values.

Regards,
Bhupinder

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