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

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Date:   Sun, 5 Apr 2020 16:33:17 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     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>,
        "rdunlap@...radead.org" <rdunlap@...radead.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

> 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.

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.

Thanks,
-- Dexuan