Re: [PATCH v4] add support for libvirt-like channels

[David Vrabel <david.vrabel@citrix.com>]

On 07/08/14 14:37, Dave Scott wrote:
> 
> On 28 Jul 2014, at 15:22, David Vrabel <david.vrabel@citrix.com> wrote:
> 
>> On 22/07/14 16:05, David Scott wrote:
>>>
>>> Note: I've seen a problem with some Linux console frontends which attempt
>>> to overwrite the read-only key 'type' (= xenconsoled|ioemu) in the frontend
>>> directory. [ this key is already present, it's not added by these patches ]
>>> Since 'type' refers to the toolstack's choice of implementation service
>>> (which is none of the guest's business) I think the read/only permissions
>>> are right. The location of the key is not ideal (it should be in the
>>> backend directory IMHO) but this is the case with several other keys located
>>> in the frontend such as 'limit' and 'tty'. I think this is a Linux frontend
>>> bug which should be fixed there. These patches work with Mirage VMs and
>>> with Linux if I workaround the permissions by giving the guest read/write
>>> to the 'type' key. 
>>
>> Which Linux front ends?
> 
> I just tested a Debian jessie with
> 
>   # uname -a
>   Linux jessie 3.13-6-686-pae #1 SMP Debian 3.13.5-1 (2014-03-04) i686 GNU/Linux
> 
> In my xenstored access log I see:
> 
>   Aug  7 14:28:30 localhost xenstored:  D40.6        write     device/console/1/ring-ref 8
>   Aug  7 14:28:30 localhost xenstored:  D40.6        write     device/console/1/port 10
>   Aug  7 14:28:30 localhost xenstored:  D40.6        write     device/console/1/type ioemu
> 
> — I think the last line is suspicious.

This was introduced by Stefano in 3.4 with 02e19f9c7cac (hvc_xen:
implement multiconsole support).

Stefano, can you advise on whether it it safe to remove the write of the
"type" key or whether we need to make it conditional on it being absent.

David