Re: [Xen-devel] [PATCH v5] modify the IO_TLB_SEGSIZE and IO_TLB_DEFAULT_SIZE configurable as flexible requirement about SW-IOMMU.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.03.15 at 09:52, <xiaoming.wang@xxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Thursday, March 5, 2015 4:40 PM
>> >>> On 05.03.15 at 04:53, <xiaoming.wang@xxxxxxxxx> wrote:
>> >> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
>> >> Sent: Thursday, March 5, 2015 3:43 AM On Tue, Mar 03, 2015 at
>> >> 04:11:09PM +0800, Wang Xiaoming wrote:
>> >> > @@ -101,13 +119,32 @@ setup_io_tlb_npages(char *str)  {
>> >> >         if (isdigit(*str)) {
>> >> >                 io_tlb_nslabs = simple_strtoul(str, &str, 0);
>> >> > -               /* avoid tail segment of size < IO_TLB_SEGSIZE */
>> >> > -               io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
>> >> >         }
>> >> >         if (*str == ',')
>> >> >                 ++str;
>> >> > -       if (!strcmp(str, "force"))
>> >> > +       if (!strncmp(str, "force", 5)) {
>> >> >                 swiotlb_force = 1;
>> >> > +               str += 5;
>> >> > +       }
>> >>
>> >> So the format is now:
>> >>
>> >>   Format: { <int> | force | <int> | <int>}
>> >>
>> >> which means I can do
>> >>   32,22323,force
>> >>
>> >> Or
>> >>   force,32
>> >>
>> >> Or
>> >>   32,force
>> >>
>> > If I use Format: { <int>,force,<int>,<int>} 32,22323,force can't
>> > acceptable.
>> > There are three  <int>  here, if there are out of order, that will
>> > cause confuse.
>> > Only       32,force,32323
>> > Or 32,,32323,2322
>> > Or ,,323222,3232
>> > Are available.
>> 
>> You need to make sure that all previously valid variants are still usable, 
> i.e.
>> force alone, a number alone, force,<number> and <number>,force. How
>> many variants you want to support with your additions is mostly up to you;
>> I'd recommend permitting force in any position.
>> 
> I don't think it's suitable to accept that "force" in any position.
> If we defined Format: { <int>,force,<int>,<int>}
> "force" must be located in second position. 
> And we add comment for each <int> also.
> Every position may be defined specifically.

As said, with the old format allowing force in either first or second
position, you have to at least accept that in the new version too.
Accepting force in any position would be a (desirable) courtesy to
the user.

Jan


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