netdev - Re: [RFC net-next v2 3/5] net: psample: add user cookie

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Date: Mon, 8 Apr 2024 22:28:40 +0200
From: Ilya Maximets <i.maximets@....org>
To: Adrian Moreno <amorenoz@...hat.com>, netdev@...r.kernel.org
Cc: i.maximets@....org, jiri@...nulli.us, xiyou.wangcong@...il.com,
 cmi@...dia.com, yotam.gi@...il.com, aconole@...hat.com, echaudro@...hat.com,
 horms@...nel.org
Subject: Re: [RFC net-next v2 3/5] net: psample: add user cookie

On 4/8/24 21:28, Adrian Moreno wrote:
> 
> 
> On 4/8/24 15:19, Ilya Maximets wrote:
>> [copying my previous reply since this version actually has netdev@ in Cc]
>>
>> On 4/8/24 14:57, Adrian Moreno wrote:
>>> Add a user cookie to the sample metadata so that sample emitters can
>>> provide more contextual information to samples.
>>>
>>> If present, send the user cookie in a new attribute:
>>> PSAMPLE_ATTR_USER_COOKIE.
>>>
>>> Signed-off-by: Adrian Moreno <amorenoz@...hat.com>
>>> ---
>>>   include/net/psample.h        |  2 ++
>>>   include/uapi/linux/psample.h |  1 +
>>>   net/psample/psample.c        | 12 +++++++++++-
>>>   3 files changed, 14 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/include/net/psample.h b/include/net/psample.h
>>> index 0509d2d6be67..2503ab3c92a5 100644
>>> --- a/include/net/psample.h
>>> +++ b/include/net/psample.h
>>> @@ -25,6 +25,8 @@ struct psample_metadata {
>>>   	   out_tc_occ_valid:1,
>>>   	   latency_valid:1,
>>>   	   unused:5;
>>> +	u8 *user_cookie;
>>
>> The code doesn't take ownership of this data.  It should probably
>> be a const pointer in this case.
>>
>> This should also allow us to avoid a double copy first to the
>> psample_metadata and then to netlink skb, as users will know that
>> it is a const pointer and so they can hand the data directly.
>>
> 
> Yep. You're right.
> 
> 
>>> +	u32 user_cookie_len;

BTW, u32 looks a little strange here and by extension in tc and OVS
as well.  We can't push move than 64K through netlink, AFAIK, so
u16 should be plenty here.  In practice, I hope, we'll not go over
u8 though.

Best regards, Ilya Maximets.