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

[Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx>]

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().
>
> I think that is the right way to do it.
>
>
>> 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.
>
> Double check the permissions of those nodes with xenstore-ls -p. Make
> sure there are no races between libxl writing the nodes and xenconsoled
> reading them.

xenstore-ls -p" shows that the vuart node is created successfully. I
have pasted below the relevant part of the command output:

   vuart = ""   (n0,r1)
    backend = "/local/domain/0/backend/vuart/1/0"   (n0,r1)
    0 = ""   (n0,r1)
     port = "1"   (n0,r1)
     ring-ref = "233475"   (n0,r1)
     limit = "1048576"   (n0,r1)
     type = "xenconsoled"   (n0,r1)
   console = ""   (n0,r1)
    backend = "/local/domain/0/backend/console/1/0"   (n0,r1)
    backend-id = "0"   (n1,r0)
    limit = "1048576"   (n0,r1)
    type = "xenconsoled"   (n0,r1)
    output = "pty"   (n0,r1)
    tty = "/dev/pts/0"   (n0,r1)
    port = "3"   (n0,r1)
    ring-ref = "233472"   (n0,r1)

The vuart node exists at /local/domain/1/vuart. I am creating the
vuart node just before the pv console node to make sure that vuart
node becomes visible before the pv console node is created. The values
are populated properly in the vuart node. Still when xenconsoled tries
to read /loca/domain/1/vuart/0/ring-ref or
/loca/domain/1/vuart/0/port, the read fails.

PV console node reads happen properly even though both nodes exist at
the same level and their access permissions are also same.

Regards,
Bhupinder

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