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

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Message-ID: <8737wuk9g6.fsf@linux.vnet.ibm.com>
Date:	Wed, 28 Oct 2015 23:47:19 +0300
From:	Alexander Yarygin <yarygin@...ux.vnet.ibm.com>
To:	Hemant Kumar <hemant@...ux.vnet.ibm.com>
Cc:	David Ahern <dsahern@...il.com>, linux-kernel@...r.kernel.org,
	srikar@...ux.vnet.ibm.com, yarygin@...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


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.

It's not a real problem anyway :)

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

>> -----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

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