Re: [PATCH net] bpf: xdp: fallback to SKB mode if DRV flag is absent.

[Nikolay Aleksandrov <razor@blackwall.org>]

On 15/10/2024 13:46, Nikolay Aleksandrov wrote:
> On 15/10/2024 13:38, Hangbin Liu wrote:
>> On Tue, Oct 15, 2024 at 12:53:08PM +0300, Nikolay Aleksandrov wrote:
>>> On 15/10/2024 11:17, Daniel Borkmann wrote:
>>>> On 10/15/24 5:36 AM, Hangbin Liu wrote:
>>>>> After commit c8a36f1945b2 ("bpf: xdp: Fix XDP mode when no mode flags
>>>>> specified"), the mode is automatically set to XDP_MODE_DRV if the driver
>>>>> implements the .ndo_bpf function. However, for drivers like bonding, which
>>>>> only support native XDP for specific modes, this may result in an
>>>>> "unsupported" response.
>>>>>
>>>>> In such cases, let's fall back to SKB mode if the user did not explicitly
>>>>> request DRV mode.
>>>>>
>>>
>>> So behaviour changed once, now it's changing again.. 
>>
>> This should not be a behaviour change, it just follow the fallback rules.
>>
> 
> hm, what fallback rules? I see dev_xdp_attach() exits on many errors
> with proper codes and extack messages, am I missing something, where's the
> fallback?
> 

Oh did you mean dev_xdp_mode()'s ndo_bpf check to decide which mode to use ?

So you'd like to do that for the unsupported bond modes as well, then I'd go
with Daniel's suggestion in that case and keep it in the bonding until
something else needs it.