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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 5 May 2017, Bhupinder Thakur wrote:
> 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)

Why is this here instead of under vuart/0?
Also, if these are the frontend nodes, where are the backend vuart nodes?


>     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.

I don't know. I would add more debug printfs to the code until I
understood what was going on.


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