patches for DPDK stable branches
 help / color / mirror / Atom feed
From: Morten Brørup <mb@smartsharesystems.com>
To: "Olivier Matz" <olivier.matz@6wind.com>
Cc: "Hongzhi Guo" <guohongzhi1@huawei.com>, <dev@dpdk.org>,
	<stable@dpdk.org>, <stephen@networkplumber.org>,
	<thomas@monjalon.net>, <konstantin.ananyev@intel.com>,
	<ferruh.yigit@intel.com>, <nicolas.chautru@intel.com>,
	<zhoujingbin@huawei.com>, <chenchanghu@huawei.com>,
	<jerry.lilijun@huawei.com>, <haifeng.lin@huawei.com>
Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH] net: fix unneeded replacement of 0 by ffff for TCP checksum
Date: Fri, 10 Jul 2020 15:56:11 +0200
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35C6111B@smartserver.smartshare.dk> (raw)
In-Reply-To: <20200710134102.GC5869@platinum>

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Olivier Matz
> Sent: Friday, July 10, 2020 3:41 PM
> 
> On Fri, Jul 10, 2020 at 03:29:36PM +0200, Morten Brørup wrote:
> > > From: Olivier Matz [mailto:olivier.matz@6wind.com]
> > > Sent: Friday, July 10, 2020 3:16 PM
> > >
> > > On Fri, Jul 10, 2020 at 03:10:34PM +0200, Morten Brørup wrote:
> > > > > From: Olivier Matz [mailto:olivier.matz@6wind.com]
> > > > > Sent: Friday, July 10, 2020 2:41 PM
> > > > >
> > > > > On Fri, Jul 10, 2020 at 02:55:51PM +0800, Hongzhi Guo wrote:
> > > > > > Per RFC768:
> > > > > > If the computed checksum is zero, it is transmitted as all
> ones.
> > > > > > An all zero transmitted checksum value means that the
> transmitter
> > > > > > generated no checksum.
> > > > > >
> > > > > > RFC793 for TCP has no such special treatment for the checksum
> of
> > > > > zero.
> > > > > >
> > > > > > Fixes: 6006818cfb26 ("net: new checksum functions")
> > > > > > Cc: stable@dpdk.org
> > > > > >
> > > > > > Signed-off-by: Hongzhi Guo <guohongzhi1@huawei.com>
> > > > > > ---
> > > > > > v2:
> > > > > > * Fixed commit tile
> > > > > > * Fixed the API comment
> > > > > > ---
> > > > > > ---
> > > > > >  lib/librte_net/rte_ip.h | 18 +++++++++++++++---
> > > > > >  1 file changed, 15 insertions(+), 3 deletions(-)
> > > > > >
> > > > > > diff --git a/lib/librte_net/rte_ip.h
> b/lib/librte_net/rte_ip.h
> > > > > > index 292f63fd7..d03c77120 100644
> > > > > > --- a/lib/librte_net/rte_ip.h
> > > > > > +++ b/lib/librte_net/rte_ip.h
> > > > > > @@ -325,7 +325,7 @@ rte_ipv4_phdr_cksum(const struct
> rte_ipv4_hdr
> > > > > *ipv4_hdr, uint64_t ol_flags)
> > > > > >   *   The pointer to the beginning of the L4 header.
> > > > > >   * @return
> > > > > >   *   The complemented checksum to set in the IP packet
> > > > > > - *   or 0 on error
> > > > > > + *   or 0 if the IP length is invalid in the header.
> > > > > >   */
> > > > > >  static inline uint16_t
> > > > > >  rte_ipv4_udptcp_cksum(const struct rte_ipv4_hdr *ipv4_hdr,
> const
> > > > > void *l4_hdr)
> > > >
> > > > 0 is a valid return value, so I suggest omitting it from the
> return
> > > value description:
> > > >
> > > >   * @return
> > > > - *   The complemented checksum to set in the IP packet
> > > > - *   or 0 on error
> > > > + *   The complemented checksum to set in the IP packet.
> > > >
> > > > The comparison "if (l3_len < sizeof(struct rte_ipv4_hdr))" is
> only
> > > there to protect against invalid input; it prevents l4_len from
> > > becoming negative.
> > >
> > > I don't get why "0 if the IP length is invalid in the header"
> should
> > > be removed from the comment: 0 is both a valid return value and
> > > the value returned on invalid packet.
> >
> > To avoid confusion. We do not want people to add error handling for a
> return value of 0.
> >
> > 0 is not a special value or an error, so it does not deserve explicit
> mentioning.
> >
> > If we want to mention the return value for garbage input, we should
> not use the wording "or 0", because this suggests that 0 is not a
> normal return value.
> 
> Ok, got it.
> 
> So maybe this?
> 
>  The complemented checksum to set in the IP packet. If
>  the IP length is invalid in the header, it returns 0.
> 
It still mentions 0 as a special value, increasing the risk of the defensive user adding "error handling" for a return value of 0.

How about this?

 The complemented checksum to set in the IP packet. If
 the IP length is invalid in the header, the return value
 is undefined.

> 
> >
> > >
> > > > For the same reason, unlikely() should be added to this
> comparison.
> > >
> > > Maybe yes, but that's another story I think.
> >
> > Agree. I was just mentioning it so it can be done when modifying the
> function anyway.
> >
> > >
> > > > Otherwise,
> > > >
> > > > Acked-by: Morten Brørup <mb@smartsharesystems.com>
> > > >
> >


  reply	other threads:[~2020-07-10 13:56 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-10  6:55 [dpdk-stable] " Hongzhi Guo
2020-07-10 12:41 ` Olivier Matz
2020-07-10 13:10   ` Morten Brørup
2020-07-10 13:16     ` Olivier Matz
2020-07-10 13:29       ` Morten Brørup
2020-07-10 13:41         ` Olivier Matz
2020-07-10 13:56           ` Morten Brørup [this message]
2020-07-10 14:40             ` [dpdk-stable] [dpdk-dev] " Olivier Matz
2020-07-10 14:52               ` Olivier Matz
2020-07-10 21:03               ` Thomas Monjalon

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=98CBD80474FA8B44BF855DF32C47DC35C6111B@smartserver.smartshare.dk \
    --to=mb@smartsharesystems.com \
    --cc=chenchanghu@huawei.com \
    --cc=dev@dpdk.org \
    --cc=ferruh.yigit@intel.com \
    --cc=guohongzhi1@huawei.com \
    --cc=haifeng.lin@huawei.com \
    --cc=jerry.lilijun@huawei.com \
    --cc=konstantin.ananyev@intel.com \
    --cc=nicolas.chautru@intel.com \
    --cc=olivier.matz@6wind.com \
    --cc=stable@dpdk.org \
    --cc=stephen@networkplumber.org \
    --cc=thomas@monjalon.net \
    --cc=zhoujingbin@huawei.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

patches for DPDK stable branches

This inbox may be cloned and mirrored by anyone:

	git clone --mirror https://inbox.dpdk.org/stable/0 stable/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 stable stable/ https://inbox.dpdk.org/stable \
		stable@dpdk.org
	public-inbox-index stable

Example config snippet for mirrors.
Newsgroup available over NNTP:
	nntp://inbox.dpdk.org/inbox.dpdk.stable


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git