Re: [PATCH v9 1/1] net/af_xdp: introduce AF XDP PMD driver

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

On 4/3/2019 3:22 PM, Ye Xiaolong wrote:
> On 04/03, Ferruh Yigit wrote:
> [snip]
>>
>> It seems, 'tools/include/asm/barrier.h' is required for 'smp_wmb()' &
>> 'smp_rmb()' in 'xsk.h'.
>> We have equivalents of these in DPDK [1], and perhaps it can be possible to use
>> them and not include this header at all.
>>
>> in 'rte_eth_af_xdp.c', before including 'xsk.h', we can include an local
>> compatibility header which does following should work:
>> #define smp_rmb() rte_rmb()
>> #define smp_wmb() rte_wmb()
>>
>> @Xiaolong, what do you think?
> 
> It sounds perfect to me, I'll take it in my next version.
> Something to confirm, So we can now assume af_xdp pmd user would use kernel (say v5.1-rc4) 
> that contains fixes regarding to xsk.h and libelf, I still need to do following
> changes.
> 
> 1. I shall use <bpf/xsk.h> as xsk.h should be installed in system folders.
> 2. `-lelf` is not needed in rte.app.mk
> 3. I need to document the libbpf build and install steps in af_xdp.rst
> 4. add the above two defines before including xsk.h

Looks good to me,
only for item 4) instead of putting those defines into .c file directly, can
create a private header in driver folder, put those lines and I assume will need
a few includes for rte_rmb as well, and include that header before xsk.h.

> 
> Thanks,
> Xiaolong
> 
> 
>>
>> [1]
>> https://git.dpdk.org/dpdk/tree/lib/librte_eal/common/include/arch/x86/rte_atomic.h?h=v19.02#n30
>>
>>>
>>> The one in tools/include also is GPL-2.0 only so it cannot be included
>>> from the PMD, which is BSD-3-clause only (and it recursively includes
>>> the other arch-specific kernel headers)
>>>
>>>> Anyway, as Xiaolong mentioned, following is working, can it work from
>>>> a distro
>>>> point of view:
>>>> - get kernel source code (>= v5.1-rc1)
>>>> - build libbfp and install
>>>> - set 'RTE_KERNELDIR' to point kernel source path
>>>> - build dpdk with af_xdp enabled
>>>
>>> As long as the full kernel tree is required, we cannot enable it in
>>> Debian and Ubuntu - we can't have it at build time on the build
>>> workers, and also there's the licensing problem.
>>
>> Got it.
>>
>> In above steps, 'libbpf' also build from kernel source tree, will it be problem
>> in you builds to not have it build from source?
>>
>> If not, taking into account that xsk.h also will be fixed, only
>> 'tools/include/asm/barrier.h' remains the problem, and it looks like it can be
>> solved, please check above.
>>
>>
>>>
>>>>> Also, the license in asm/barrier.h is GPL-2.0 only. It is not a
>>>>> userspace header so it is not covered by the userspace exception,
>>>>> which
>>>>> means at the very least the af_xdp PMD shared object is also
>>>>> licensed
>>>>> under GPL-2.0 only, isn't it?
>>>>>
>>>>
>>>>
>>