netdev - Re: [PATCH net] skbuff.h: Improve the checksum related comments

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Date:   Sun, 5 Apr 2020 09:41:24 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Dexuan Cui <decui@...rosoft.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "willemb@...gle.com" <willemb@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "simon.horman@...ronome.com" <simon.horman@...ronome.com>,
        "sdf@...gle.com" <sdf@...gle.com>,
        "john.hurley@...ronome.com" <john.hurley@...ronome.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "fw@...len.de" <fw@...len.de>,
        "jonathan.lemon@...il.com" <jonathan.lemon@...il.com>,
        "pablo@...filter.org" <pablo@...filter.org>,
        "jeremy@...zel.net" <jeremy@...zel.net>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] skbuff.h: Improve the checksum related comments

On 4/5/20 9:33 AM, Dexuan Cui wrote:
>> From: Matthew Wilcox <willy@...radead.org>
>> Sent: Sunday, April 5, 2020 3:36 AM
>> To: Dexuan Cui <decui@...rosoft.com>
>>
>> On Sun, Apr 05, 2020 at 12:17:43AM -0700, Dexuan Cui wrote:
>>>   * CHECKSUM_COMPLETE:
>>>   *
>>> - *   This is the most generic way. The device supplied checksum of the
>> _whole_
>>> - *   packet as seen by netif_rx() and fills out in skb->csum. Meaning, the
>>> + *   This is the most generic way. The device supplies checksum of the
>> _whole_
>>> + *   packet as seen by netif_rx() and fills out in skb->csum. This means the
>>
>> I think both 'supplies' and 'supplied' are correct in this sentence.  The
>> nuances are slightly different, but the meaning is the same in this instance.
> 
> I see. So let me rever back to "supplied".
>  
>> You missed a mistake in the second line though, it should be either 'fills
>> out' or 'fills in'.  I think we tend to prefer 'fills in'.
> 
> Thanks! Will use "fills in" in v2.
> 
>>>   * CHECKSUM_COMPLETE:
>>>   *   Not used in checksum output. If a driver observes a packet with this
>> value
>>> - *   set in skbuff, if should treat as CHECKSUM_NONE being set.
>>> + *   set in skbuff, the driver should treat it as CHECKSUM_NONE being set.
>>
>> I would go with "it should treat the packet as if CHECKSUM_NONE were set."
> 
> Thanks. Will use this version.
>  
>>> @@ -211,7 +211,7 @@
>>>   * is implied by the SKB_GSO_* flags in gso_type. Most obviously, if the
>>>   * gso_type is SKB_GSO_TCPV4 or SKB_GSO_TCPV6, TCP checksum offload
>> as
>>>   * part of the GSO operation is implied. If a checksum is being offloaded
>>> - * with GSO then ip_summed is CHECKSUM_PARTIAL, csum_start and
>> csum_offset
>>> + * with GSO then ip_summed is CHECKSUM_PARTIAL AND csum_start and
>> csum_offset
>>>   * are set to refer to the outermost checksum being offload (two offloaded
>>>   * checksums are possible with UDP encapsulation).
>>
>> Why the capitalisation of 'AND'?
> 
> The current text without the patch is:
>  * part of the GSO operation is implied. If a checksum is being offloaded
>  * with GSO then ip_summed is CHECKSUM_PARTIAL, csum_start and csum_offset
>  * are set to refer to the outermost checksum being offload (two offloaded
>  * checksums are possible with UDP encapsulation).
> 
> The comma after the "CHECKSUM_PARTIAL" seems suspicious to me. I feel we
> should add an "and" after the comma, or replace the comma with "and", but
> either way we'll have "... and csum_start and csum_offset...", which seems a little
> unnatural to me since we have 2 'and's here... So I tried to make it a little natural
> by replacing the first 'and' with 'AND', which obviously causes confusion to you.

maybe "both csum_start and csum_offset are set to refer to".

> Please suggest the best change here. Thanks!
>  
>> Thanks for the improvements,
>>
>> Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> 
> Thanks for the comments! I'll wait for your suggestion on the 'AND' and post
> a v2.


-- 
~Randy