Re: [Xen-devel] [PATCH v3 1/2] gnttab: don't use possibly unbounded tail calls

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.08.17 at 17:04, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 15/08/17 14:49, Jan Beulich wrote:
>> @@ -2608,7 +2610,7 @@ static long gnttab_copy(
>>      {
>>          if ( i && hypercall_preempt_check() )
>>          {
>> -            rc = i;
>> +            rc = count - i;
> 
> Somewhere, probably as a comment for gnttab_copy(), we should have a
> comment explaining why the return value is different from all other ops,
> which will also go somewhat to explaining the "rc = count - rc;" logic.

Sure.

> I think it would also be wise to have an early exit in
> do_grant_table_op() for passing a count of 0.  As far as I can tell, we
> will get all the way into the subop handler before discovering a count of 0.

Well, that would collide with {get,set}_version which don't currently
honor count (and hence existing callers may be passing zero here).
Otherwise I would agree with what you propose.

Jan


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