[Xen-devel] Re: [PATCH v3] libvchan: interdomain communications library

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 09/01/2011 12:56 PM, Ian Jackson wrote:
> Daniel De Graaf writes ("Re: [PATCH v3] libvchan: interdomain communications 
> library"):
>> Making this change has exposed an interesting ordering dependency in the
>> notify API under Linux: the file descriptor for gntdev or gntalloc must be
>> less than the file descriptor for evtchn in order for the event channel to
>> still be active when the unmap occurs on a crash. The init functions of
>> libvchan do open the files in the proper order for this to happen.
> 
> Wow, that's pretty crazy.  Surely the gnt* fd should have an internal
> reference to the evtchn fd ?
> 
> Ian.
> 

The gnt* drivers will need to be changed to both find and take such a
reference; currently, they only refer to the port. This will probably
add a dependency from the gnt* module on evtchn; I'll look at what is
actually required to hold the event channel open when I make the patch.


-- 
Daniel De Graaf
National Security Agency

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