Re: [Xen-devel] libvchan-error

[Shakeel Butt <shakeel.butt@xxxxxxxxx>]

On Wed, May 8, 2013 at 9:34 AM, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
> On 05/07/2013 11:43 PM, Shakeel Butt wrote:
>>
>> On Fri, May 3, 2013 at 7:23 AM, Khandelwal, Shubham
>> <Shubham.Khandelwal@xxxxxxxxxx> wrote:
>>>
>>> Hi,
>>>
>>>
>>>
>>> I am trying to use the libvchan tool for Inter domain communication for
>>> XEN-ARM on Fast Model for VExpress platform. I have successfully compiled
>>> it
>>> and ported the following in the rootfs :
>>>
>>> libxenvchan.so, libxenvchan.so.1.0, libxenvchan.so.1.0.0, libxenvchan.a,
>>> vchan-node1, vchan-node2.
>>>
>>>
>>>
>>> But when I am using it shows the following error in both dom0 and domU.
>>>
>>> …
>>>
>>> # vchan-node1 server read 1 1536
>>>
>>> libxenvchan_*_init: No such file or directory
>>>
>>> …
>>>
>>>
>>>
>>> Am I missing some files here ?
>>>
>> Are you running the server in Dom0? If yes then check “xenstore-read
>> /local/domain/0/domid”, if nothing is there, write 0 to it.
>>
>> The server side of libvchan reads its id from xenstore and use it to
>> remove its permission over the nodepath. Not sure why? (CCed to
>> Daniel, any particular reason)
>
>
> It does not remove its own permission; instead, it sets itself as the
> owner for the nodes when changing permissions. Element 0 in a xenstore
> permission list describes owner for the domid and "other" for the r/w
> bits, a common source of confusion.

So is "XS_PERM_NONE" for ownership? and not for no access?

> Reading the "domid" node was the simplest way for a domain to determine
> its own domid, which is required to do this.  If dom0 commonly does not
> have this node, it may be preferable to switch to making a get-permission
> call on the node you just created instead, and assume that you are the
> owner of that node.

The server is using domid to set its permission on the nodepath (+ring-ref &
+event-channel) to XS_PERM_NONE. Does this really needed?

>
>>>
>>>
>>>
>>>
>>> Regards
>>>
>>>
>>>
>>> Shubham Khandelwal
>
>
>
> --
> Daniel De Graaf
> National Security Agency

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