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

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 2/2/2017 10:37 AM, Adrien Mazarguil wrote:
> On Thu, Feb 02, 2017 at 10:15:08AM +0000, Ferruh Yigit wrote:
>> 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@dpdk.org
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Shahaf Shuler <shahafs@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.
> 
> Right, what I'm getting at is this code is supposed to work regardless of
> the running kernel version (uname -r), userland headers version
> (/usr/include/linux) and source tree version (/usr/src/linux/), all of them
> may differ. Basically this PMD can be built on a system and run on another
> since it's not a kernel module. In short the following scenarios should be
> handled:
> 
> - Kernel (uname -r) is 3.2, /usr/include/linux comes from 4.5, and
>   /usr/src/linux comes from 4.10.
> 
> - Kernel (uname -r) is 4.10, /usr/include/linux comes from 3.2 and 
>   /usr/src/linux does not even exist.
> 
> - Kernel (uname -r) is 4.8, /usr/include/linux comes from 4.9.
> 
> - Kernel (uname -r) is 4.9, /usr/include/linux comes from 4.9 (when one gets
>   lucky enough).
> 
>>> - 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?
> 
> You're right, ETHTOOL_GLINKSETTINGS should be consistent with
> LINUX_VERSION_CODE since both includes come from the same
> directory. We normally don't need to manage the case where a system has
> broken includes, however as you're pointing out below distributions
> sometimes make backports and the kernel version means nothing. Relying on
> ETHTOOL_GLINKSETTINGS's presence makes more sense.
> 
>>> 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.
> 
> My thought as well.
> 
>> 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
> 
> Yeah, especially since it's not a kernel module, a PMD must perform a
> runtime version check.
> 
>>> Ferruh, please revert.
>>
>>
>> But original patch looks good, I will convert it to initial patch, and
>> keep it until above two items clarified.
> 
> I've talked to Shahaf/Nelio, they already intend to send an updated version
> due to the above concerns. Do you prefer a fix on top of it?

No, if there will be a new version, I will drop the existing one in the
repo.

> 
>>> stable@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,
>>>>>>>>> <...>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>