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Date: Fri, 10 Jul 2020 15:16:04 +0200
From: Olivier Matz <olivier.matz@6wind.com>
To: Morten =?iso-8859-1?Q?Br=F8rup?= <mb@smartsharesystems.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,
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Subject: Re: [dpdk-stable] [PATCH] net: fix unneeded replacement of 0 by
ffff for TCP checksum
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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.
> For the same reason, unlikely() should be added to this comparison.
Maybe yes, but that's another story I think.
> Otherwise,
>
> Acked-by: Morten Brørup <mb@smartsharesystems.com>
>