netdev - Re: [PATCH net-next v4 2/4] net: tap: track dropped skb via kfree_skb

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Date:   Wed, 2 Mar 2022 09:43:29 -0800
From:   Dongli Zhang <dongli.zhang@...cle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, davem@...emloft.net,
        rostedt@...dmis.org, mingo@...hat.com, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, imagedong@...cent.com,
        joao.m.martins@...cle.com, joe.jin@...cle.com, dsahern@...il.com,
        edumazet@...gle.com
Subject: Re: [PATCH net-next v4 2/4] net: tap: track dropped skb via
 kfree_skb_reason()

Hi Jakub,

On 3/1/22 6:42 PM, Jakub Kicinski wrote:
> On Sat, 26 Feb 2022 00:49:27 -0800 Dongli Zhang wrote:
>> +	SKB_DROP_REASON_SKB_CSUM,	/* sk_buff checksum error */
> 
> Can we spell it out a little more? It sounds like the checksum was
> incorrect. Will it be clear that computing the checksum failed, rather
> than checksum validation failed?

I am just trying to make the reasons as generic as possible so that:

1. We may minimize the number of reasons.

2. People may re-use the same reason for all CSUM related issue.

> 
>> +	SKB_DROP_REASON_SKB_COPY_DATA,	/* failed to copy data from or to
>> +					 * sk_buff
>> +					 */
> 
> Here should we specify that it's copying from user space?

Same as above. I am minimizing the number of reasons so that any memory copy for
sk_buff may re-use this reason.

Please let me know if you think it is very significant to specialize the usage
of reason. I will then add "sk_buff csum computation failed" and "userspace".

> 
>> +	SKB_DROP_REASON_SKB_GSO_SEG,	/* gso segmentation error */
>> +	SKB_DROP_REASON_DEV_HDR,	/* there is something wrong with
>> +					 * device driver specific header
>> +					 */
> 
> How about:
> device driver specific header / metadata was invalid
> 
> to broaden the scope also to devices which don't transfer the metadata
> in form of a header?

I will add 'metadata'.

Thank you very much!

Dongli Zhang

> 
>> +	SKB_DROP_REASON_FULL_RING,	/* ring buffer is full */