Re: [dpdk-dev] [PATCH] net: fix unneeded replacement of 0 by ffff for TCP checksum

["Morten Brørup" <mb@smartsharesystems.com>]

> 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.

For the same reason, unlikely() should be added to this comparison.

Otherwise,

Acked-by: Morten Brørup <mb@smartsharesystems.com>