Re: [win-pv-devel] Detecting event channel disconnect

[RafaÅ WojdyÅa <omeg@xxxxxxxxxxxxxxxxxxxxxx>]

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On 2015-05-18 16:26, Paul Durrant wrote:
>> -----Original Message----- From: 
>> win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx [mailto:win-pv-devel- 
>> bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of Rafal Wojdyla Sent:
>> 18 May 2015 15:14 To: win-pv-devel@xxxxxxxxxxxxxxxxxxxx Subject: 
>> [win-pv-devel] Detecting event channel disconnect
>> 
> Hello,
> 
> Am I correct in the assumption that currently a Windows event 
> channel peer can't easily detect if the other peer has closed the 
> remote end?
> 
>> Yes, that's correct. There's no interface exposed for that.
> 
> I'm not 100% sure on how the low-level evtchn hypervisor API works 
> in that case but it seems that there's no notification.
> 
> If the above is correct I think adding a EVTCHNOP_status call to 
> xenbus API would allow for easy status querying.
> 
> 
>> Yes, wiring that through the EVTCHN interface - with suitable 
>> abstraction - sounds ok. However, it does beg the question of
>> why the guest needs to know?
> 
>> Paul

That's a good question - in our old vchan implementation the server
used such call to check if the remote domain dies before connecting.
It relied on a quirk in EVTCHNOP_status which may or may not be a bug
(call returns a different error code depending whether the remote
domain doesn't exist or just the port is invalid). Honestly such check
should probably be replaced by a timeout period on our end...

- -- 
RafaÅ WojdyÅa
Qubes Tools for Windows developer
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