linux-kernel - Re: [PATCH v9 1/4] perf,kvm/{x86,s390}: Remove dependency on uapi/kvm

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Date:	Thu, 29 Oct 2015 12:37:18 +0530
From:	Hemant Kumar <hemant@...ux.vnet.ibm.com>
To:	Alexander Yarygin <yarygin@...ux.vnet.ibm.com>
CC:	David Ahern <dsahern@...il.com>, linux-kernel@...r.kernel.org,
	srikar@...ux.vnet.ibm.com, acme@...nel.org, borntraeger@...ibm.com,
	mingo@...hat.com, paulus@...ba.org, scottwood@...escale.com,
	naveen.n.rao@...ux.vnet.ibm.com, sukadev@...ux.vnet.ibm.com,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v9 1/4] perf,kvm/{x86,s390}: Remove dependency on uapi/kvm_perf.h



On 10/29/2015 02:17 AM, Alexander Yarygin wrote:
> Hemant Kumar writes:
>
>> Hi David,
>>
>>
>> On 10/07/2015 09:41 PM, David Ahern wrote:
>>> On 10/6/15 8:25 PM, Hemant Kumar wrote:
>>>> @@ -358,7 +357,12 @@ static bool handle_end_event(struct
>>>> perf_kvm_stat *kvm,
>>>>        time_diff = sample->time - time_begin;
>>>>
>>>>        if (kvm->duration && time_diff > kvm->duration) {
>>>> -        char decode[DECODE_STR_LEN];
>>>> +        char *decode = zalloc(decode_str_len);
>>> decode can still be a stack variable even with variable length.
>>>
>> Yeah, we can do that. But, I am not sure whether its a standard way.
>>
> Well, I also vote for making them variable length arrays. I guess that
> wouldn't be a problem because the "variable" here is actually a constant
> compile time value, even if it's extern.
>
> But if people are strongly against it, as an alternative I can suggest
> to move the 'char *decode' variable to the perf_kvm_stat structure,
> allocate it once e.g. in kvm_events_report() and just write to it via
> decode_key(). If I'm not mistaken, we always write \0 trimmed strings,
> so garbage after \0 shouldn't be a problem.

I agree. We can do that. But, since this is a small change (making
the variable a constant compile time value rather than the array being
a run time value), we can do that subsequently. For now, we can go
with the current patchset.

> It's not a real problem anyway :)

Yeah.

> For s390 parts:
> Acked-by: Alexander Yarygin <yarygin@...ux.vnet.ibm.com>

Thanks a lot for testing and acking it. :)

>>> -----8<-----
>>>
>>>> @@ -575,7 +581,7 @@ static void show_timeofday(void)
>>>>
>>>>    static void print_result(struct perf_kvm_stat *kvm)
>>>>    {
>>>> -    char decode[DECODE_STR_LEN];
>>>> +    char *decode;
>>> and a stack variable here too.
>>>
>> Same here.
>>
>>> David
>>> _______________________________________________
>>> Linuxppc-dev mailing list
>>> Linuxppc-dev@...ts.ozlabs.org
>>> https://lists.ozlabs.org/listinfo/linuxppc-dev

-- 
Thanks,
Hemant Kumar

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