Re: [Xen-devel] [PATCH 1/3] libxl: In domain death search, start search at first domid we want

[Jim Fehlig <jfehlig@xxxxxxxx>]

Ian Campbell wrote:
> On Tue, 2015-03-17 at 09:30 -0600, Jim Fehlig wrote:
>   
>> From: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
>>
>> From: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
>>
>> When domain_death_xswatch_callback needed a further call to
>> xc_domain_getinfolist it would restart it with the last domain it
>> found rather than the first one it wants.
>>
>> If it only wants one it will also only ask for one domain.  The result
>> would then be that it gets the previous domain again (ie, the previous
>> one to the one it wants), which still doesn't reveal the answer to the
>> question, and it would therefore loop again.
>>
>> It's completely unclear to me why I thought it was a good idea to
>> start the xc_domain_getinfolist with the last domain previously found
>> rather than the first one left un-confirmed.  The code has been that
>> way since it was introduced.
>>     
>
> Is it because the xc_domain_getinfolist will fetch at most:
>         int nentries = LIBXL_TAILQ_NEXT(evg, entry) ? 200 : 1;
> entries?
>
> After your change then if the domid we are looking for is the 201st
> domain then won't we just keep going round looking at the first 200
> (undying) domains?
>   

Yes, that theoretically looks to be the case. When all 200 domains have
been examined the inner loop is terminated

if (got == gotend) {
LIBXL__LOG(CTX, LIBXL__LOG_DEBUG, " got==gotend");
break;
}

which will repeat the outer loop with same conditions. But
xc_domain_getinfolist() is called with first_domain set to the domain ID
we are looking for. Is it possible for xc_domain_getinfolist() to return
200 domains with IDs less than the ID we asked for?

Regards,
Jim

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