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Re: [Xen-devel] [PATCH v3 39/52] xen: check parameter validity when parsing command line

On 23/08/17 15:18, Jan Beulich wrote:
>>>> On 23.08.17 at 14:42, <jgross@xxxxxxxx> wrote:
>> On 23/08/17 11:38, Jan Beulich wrote:
>>>>>> On 23.08.17 at 11:30, <jgross@xxxxxxxx> wrote:
>>>> On 22/08/17 13:24, Jan Beulich wrote:
>>>>>>>> On 16.08.17 at 14:52, <jgross@xxxxxxxx> wrote:
>>>>>> @@ -176,7 +210,8 @@ int __init parse_bool(const char *s)
>>>>>>           !strcmp("on", s) ||
>>>>>>           !strcmp("true", s) ||
>>>>>>           !strcmp("enable", s) ||
>>>>>> -         !strcmp("1", s) )
>>>>>> +         !strcmp("1", s) ||
>>>>>> +         !*s )
>>>>>>          return 1;
>>>>> Careful with this: Taking the "iommu=" example that I've commented
>>>>> on in the other patch already, much depends on what you mean to
>>>>> do about the problem there: "iommu=,..." should not end up
>>>>> meaning "iommu=on,...".
>>>> It won't. *s will be ',' in this case.
>>> Right, but as said - much depends on what you mean to do about
>>> the problem in the earlier patch.
>> So I just hit this. And looking more thoroughly into it: today it in
>> fact has exactly this meaning. iommu_enable is "1" per default. So
>> specifying "iommu=,..." won't change this and has the same semantics
>> as "iommu=on,...".
> But that's not the interesting case. Are you saying that
> "iommu=off iommu=,..." enables the IOMMU today? It doesn't
> look to me as if it would.

I guess this is a weird case after all: trying to be compatible to
"iommu=off iommu=,..." while "iommu=off iommu=on,..." doesn't work
correctly today is questionable.

OTOH the easiest way to avoid all discussions might be to drop the
parse_bool() modification to return "true" in case of an empty string
and handle this case by not calling parse_bool() at all from
_cmdline_parse() if no argument was given.


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