[dpdk-dev] [dpdk-stable] [PATCH v2] net/mlx5: fix link status query

[Ferruh Yigit]

On 2/2/2017 8:45 AM, Adrien Mazarguil wrote:
> On Wed, Feb 01, 2017 at 06:11:17PM +0000, Ferruh Yigit wrote:
>> On 2/1/2017 12:57 PM, Adrien Mazarguil wrote:
>>> On Wed, Feb 01, 2017 at 11:13:59AM +0000, Ferruh Yigit wrote:
>>>> On 2/1/2017 9:07 AM, Adrien Mazarguil wrote:
>>>>> On Wed, Feb 01, 2017 at 06:53:55AM +0000, Shahaf Shuler wrote:
>>>>>> : Tuesday, January 31, 2017 6:17 PM, Ferruh Yigit:
>>>>>>> On 1/31/2017 11:45 AM, Shahaf Shuler wrote:
>>>>>>>> Trying to query the link status through new kernel ioctl API
>>>>>>>> ETHTOOL_GLINKSETTINGS was always failing due to kernel bug.
>>>>>>>> The bug was fixed on version 4.9
>>>>>>>> this patch uses the legacy ioctl API for lower kernels.
>>>>>>>>
>>>>>>>> Fixes: 188408719888 ("net/mlx5: fix support for newer link speeds")
>>>>>>>> CC: stable at dpdk.org
>>>>>>>>
>>>>>>>> Signed-off-by: Shahaf Shuler <shahafs at mellanox.com>
>>>>>>>> ---
>>>>>>>
>>>>>>> <...>
>>>>>>>
>>>>>>>> @@ -707,7 +708,7 @@ struct priv *
>>>>>>>>  static int
>>>>>>>>  mlx5_link_update_unlocked_gs(struct rte_eth_dev *dev, int
>>>>>>>> wait_to_complete)  { -#ifdef ETHTOOL_GLINKSETTINGS
>>>>>>>> +#if KERNEL_VERSION(4, 9, 0) <= LINUX_VERSION_CODE
>>>>>>>
>>>>>>> Mostly it is not good idea to do kernel version check in the .c file.
>>>>>>>
>>>>>>> It is possible to move this comparison to the .h file, and set a feature
>>>>>>> macro based on comparison result, like HAVE_ETHTOOL_GLINKSETTINGS,
>>>>>>> and
>>>>>>> use this macro in the .c file.
>>>>>>>
>>>>>>> This makes .c code easier to understand. And the abstraction in the
>>>>>>> header file lets you update the comparison in the future without
>>>>>>> changing the code itself.
>>>>>>>
>>>>>>> But it is your call, do you prefer to continue with this one?
>>>>>>
>>>>>> This is a good suggestion. 
>>>>>> Adrien, Nélio what do you think?
>>>>>
>>>>> Let's include this patch as-is. Doing so in a header file such as mlx5.h
>>>>> would require including linux/version.h from that file and cause the entire
>>>>> PMD to be even more OS-dependent.
>>>>>
>>>>> We'll move this check elsewhere in the future if we need several such
>>>>> workarounds, thanks.
>>>>
>>>> OK.
>>>>
>>>> One more thing, comment log says:
>>>> "The bug was fixed on version 4.9"
>>>>
>>>> And code does:
>>>> "+#if KERNEL_VERSION(4, 9, 0) <= LINUX_VERSION_CODE"
>>>>
>>>> If the bug is fixed in 4.9, should check be "<" instead of "<="
>>>
>>> I'll concede the argument order used in this condition is somewhat unusual
>>> but it actually ends up being the same as:
>>>
>>>  #if LINUX_VERSION_CODE > KERNEL_VERSION(4, 9, 0)
>>
>> I don't think they are same, unless I am missing something obvious.
>>
>> "+#if KERNEL_VERSION(4, 9, 0) <= LINUX_VERSION_CODE"
>> vs
>> "#if LINUX_VERSION_CODE > KERNEL_VERSION(4, 9, 0)"
>>
>> Even if you change the argument order, one covers 4.9 release other not.
> 
> All right, turns out we're both wrong because it should have been >= anyway
> regardless of the order as you pointed out. The block must appear when
> kernel version is higher or equal to 4.9.0.

I see now, my logic was wrong, and I can see what are you trying to
explain by changing argument order, thanks ...

> 
> Now I think there are a couple of additional issues with this patch that
> require a revert and rework:
> 
> - Kernel headers do not necessarily match the running version. What if this
>   code is compiled against a 4.10.0 source tree and the running kernel is
>   4.5? How about the reverse?

It is possible to use proper kernel headers via RTE_KERNELDIR
environment variable.

But without this patch, /usr/include/linux/ethtool.h used directly in
Makefile, which has same problem you mentioned.

> 
> - By removing the check on ETHTOOL_GLINKSETTINGS, this code breaks
>   compilation for Linux kernel version < 4.5, which I think is a problem.

Please help me understand.

ETHTOOL_GLINKSETTINGS defined for kernels > 4.5, and this patch replaces
"#ifdef ETHTOOL_GLINKSETTINGS"
with
"#if KERNEL_VERSION(4, 9, 0) <= LINUX_VERSION_CODE"

So, kernel version <= 4.5 part should be same, why it is giving a
compile error?

> 
> So I believe this patch should be re-worked to maintain a check on
> ETHTOOL_GLINKSETTINGS (or define it then not present) and perform an
> additional version check at runtime to use the most appropriate ioctl API.

Overall, it would be better if you can find a way without dealing kernel
versions, which causes lots of maintenance work.

Also another issue we are experiencing while maintaining KNI is
backported kernels, they tend to break version based checks. So there
are distro based checks combined with version checks, I think this
wouldn't be something you want J

> 
> Ferruh, please revert.


But original patch looks good, I will convert it to initial patch, and
keep it until above two items clarified.

> 
> stable at dpdk.org, please ignore this commit for the the time being, and sorry
> for the noise.
> 
>>> Which is the correct intent. I guess you can update this line for clarity if
>>> you think it's necessary.
>>
>> If the intention is as following, I can fix it while applying:
>> #if KERNEL_VERSION(4, 9, 0) < LINUX_VERSION_CODE
>>
>>>
>>>>>
>>>>>>>>  	struct priv *priv = mlx5_get_priv(dev);
>>>>>>>>  	struct ethtool_link_settings edata = {
>>>>>>>>  		.cmd = ETHTOOL_GLINKSETTINGS,
>>>>>>> <...>
>>>>>
>>>>
>>>
>>
>