RE: [PATCH v4 1/2] net: add functions to calculate UDP/TCP cksum in mbuf

["Li, Xiaoyun" <xiaoyun.li@intel.com>]

Hi

> -----Original Message-----
> From: Singh, Aman Deep <aman.deep.singh@intel.com>
> Sent: Wednesday, December 15, 2021 11:34
> To: Li, Xiaoyun <xiaoyun.li@intel.com>; Yigit, Ferruh
> <ferruh.yigit@intel.com>; olivier.matz@6wind.com;
> mb@smartsharesystems.com; Ananyev, Konstantin
> <konstantin.ananyev@intel.com>; stephen@networkplumber.org;
> Medvedkin, Vladimir <vladimir.medvedkin@intel.com>
> Cc: dev@dpdk.org
> Subject: Re: [PATCH v4 1/2] net: add functions to calculate UDP/TCP cksum in
> mbuf
> 
> 
> On 12/3/2021 5:08 PM, Xiaoyun Li wrote:
> > Add functions to call rte_raw_cksum_mbuf() to calculate IPv4/6 UDP/TCP
> > checksum in mbuf which can be over multi-segments.
> >
> > Signed-off-by: Xiaoyun Li <xiaoyun.li@intel.com>
> > ---
> >   doc/guides/rel_notes/release_22_03.rst |  10 ++
> >   lib/net/rte_ip.h                       | 186 +++++++++++++++++++++++++
> >   lib/net/version.map                    |  10 ++
> >   3 files changed, 206 insertions(+)
> >
> > diff --git a/doc/guides/rel_notes/release_22_03.rst
> > b/doc/guides/rel_notes/release_22_03.rst
> > index 6d99d1eaa9..7a082c4427 100644
> > --- a/doc/guides/rel_notes/release_22_03.rst
> > +++ b/doc/guides/rel_notes/release_22_03.rst
> > @@ -55,6 +55,13 @@ New Features
> >        Also, make sure to start the actual text at the margin.
> >        =======================================================
> >
> > +* **Added functions to calculate UDP/TCP checksum in mbuf.**
> > +  * Added the following functions to calculate UDP/TCP checksum of
> packets
> > +    which can be over multi-segments:
> > +    - ``rte_ipv4_udptcp_cksum_mbuf()``
> > +    - ``rte_ipv4_udptcp_cksum_mbuf_verify()``
> > +    - ``rte_ipv6_udptcp_cksum_mbuf()``
> > +    - ``rte_ipv6_udptcp_cksum_mbuf_verify()``
> >
> >   Removed Items
> >   -------------
> > @@ -84,6 +91,9 @@ API Changes
> >      Also, make sure to start the actual text at the margin.
> >      =======================================================
> >
> > +* net: added experimental functions ``rte_ipv4_udptcp_cksum_mbuf()``,
> > +  ``rte_ipv4_udptcp_cksum_mbuf_verify()``,
> > +``rte_ipv6_udptcp_cksum_mbuf()``,
> > +  ``rte_ipv6_udptcp_cksum_mbuf_verify()``
> >
> >   ABI Changes
> >   -----------
> > diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h index
> > c575250852..534f401d26 100644
> > --- a/lib/net/rte_ip.h
> > +++ b/lib/net/rte_ip.h
> > @@ -400,6 +400,65 @@ rte_ipv4_udptcp_cksum(const struct rte_ipv4_hdr
> *ipv4_hdr, const void *l4_hdr)
> >   	return cksum;
> >   }
> >
> > +/**
> > + * @internal Calculate the non-complemented IPv4 L4 checksum of a
> > +packet  */ static inline uint16_t __rte_ipv4_udptcp_cksum_mbuf(const
> > +struct rte_mbuf *m,
> > +			     const struct rte_ipv4_hdr *ipv4_hdr,
> > +			     uint16_t l4_off)
> > +{
> > +	uint16_t raw_cksum;
> > +	uint32_t cksum;
> > +
> > +	if (l4_off > m->pkt_len)
> > +		return 0;
> > +
> > +	if (rte_raw_cksum_mbuf(m, l4_off, m->pkt_len - l4_off,
> &raw_cksum))
> > +		return 0;
> > +
> > +	cksum = raw_cksum + rte_ipv4_phdr_cksum(ipv4_hdr, 0);
> > +
> > +	cksum = ((cksum & 0xffff0000) >> 16) + (cksum & 0xffff);
> At times, even after above operation "cksum" might stay above 16-bits, ex
> "cksum = 0x1FFFF" to start with.
> Can we consider using "return __rte_raw_cksum_reduce(cksum);"

Will use it in next version. Thanks.

Also, not related to this patch. It means that __rte_ipv4_udptcp_cksum and __rte_ipv6_udptcp_cksum have the same issue, right?
Should anyone fix that?

> > +
> > +	return (uint16_t)cksum;
> > +}
> > +
> > +/**
> > + * @warning
> > + * @b EXPERIMENTAL: this API may change without prior notice.
> > + *
> > + * Compute the IPv4 UDP/TCP checksum of a packet.
> > + *
> > + * @param m
> > + *   The pointer to the mbuf.
> > + * @param ipv4_hdr
> > + *   The pointer to the contiguous IPv4 header.
> > + * @param l4_off
> > + *   The offset in bytes to start L4 checksum.
> > + * @return
> > + *   The complemented checksum to set in the L4 header.
> > + */
> > +__rte_experimental
> > +static inline uint16_t
> > +rte_ipv4_udptcp_cksum_mbuf(const struct rte_mbuf *m,
> > +			   const struct rte_ipv4_hdr *ipv4_hdr, uint16_t l4_off)
> {
> > +	uint16_t cksum = __rte_ipv4_udptcp_cksum_mbuf(m, ipv4_hdr,
> l4_off);
> > +
> > +	cksum = ~cksum;
> > +
> > +	/*
> > +	 * Per RFC 768: If the computed checksum is zero for UDP,
> > +	 * it is transmitted as all ones
> > +	 * (the equivalent in one's complement arithmetic).
> > +	 */
> > +	if (cksum == 0 && ipv4_hdr->next_proto_id == IPPROTO_UDP)
> > +		cksum = 0xffff;
> > +
> > +	return cksum;
> > +}
> > +
> >   /**
> >    * Validate the IPv4 UDP or TCP checksum.
> >    *
> > @@ -426,6 +485,38 @@ rte_ipv4_udptcp_cksum_verify(const struct
> rte_ipv4_hdr *ipv4_hdr,
> >   	return 0;
> >   }
> >
> > +/**
> > + * @warning
> > + * @b EXPERIMENTAL: this API may change without prior notice.
> > + *
> > + * Verify the IPv4 UDP/TCP checksum of a packet.
> > + *
> > + * In case of UDP, the caller must first check if
> > +udp_hdr->dgram_cksum is 0
> > + * (i.e. no checksum).
> > + *
> > + * @param m
> > + *   The pointer to the mbuf.
> > + * @param ipv4_hdr
> > + *   The pointer to the contiguous IPv4 header.
> > + * @param l4_off
> > + *   The offset in bytes to start L4 checksum.
> > + * @return
> > + *   Return 0 if the checksum is correct, else -1.
> > + */
> > +__rte_experimental
> > +static inline uint16_t
> > +rte_ipv4_udptcp_cksum_mbuf_verify(const struct rte_mbuf *m,
> > +				  const struct rte_ipv4_hdr *ipv4_hdr,
> > +				  uint16_t l4_off)
> > +{
> > +	uint16_t cksum = __rte_ipv4_udptcp_cksum_mbuf(m, ipv4_hdr,
> l4_off);
> > +
> > +	if (cksum != 0xffff)
> > +		return -1;
> cksum other than 0xffff, should return error. Is that the intent or I am
> missing something obvious.

This is the intent. This function is to verify if the cksum in the packet is correct.

It's different from calling rte_ipv4/6_udptcp_cksum_mbuf(). When calling rte_ipv4/6_udptcp_cksum_mbuf(), you need to set the cksum in udp/tcp header as 0. Then calculate the cksum.

But here, user should directly call this function with the original packet. Then if the udp/tcp cksum is correct, after the calculation (please note that, this is calling __rte_ipv4_udptcp_cksum_mbuf(), so the result needs to be ~), it should be 0xffff, namely, ~cksum = 0 which means cksum is correct. You can see rte_ipv4/6_udptcp_cksum_verify() is doing the same.

> > +
> > +	return 0;
> > +}
> > +
> >   /**
> >    * IPv6 Header
> >    */
> > @@ -538,6 +629,68 @@ rte_ipv6_udptcp_cksum(const struct rte_ipv6_hdr
> *ipv6_hdr, const void *l4_hdr)
> >   	return cksum;
> >   }
> >
> > +/**
> > + * @internal Calculate the non-complemented IPv6 L4 checksum of a
> > +packet  */ static inline uint16_t __rte_ipv6_udptcp_cksum_mbuf(const
> > +struct rte_mbuf *m,
> > +			     const struct rte_ipv6_hdr *ipv6_hdr,
> > +			     uint16_t l4_off)
> > +{
> > +	uint16_t raw_cksum;
> > +	uint32_t cksum;
> > +
> > +	if (l4_off > m->pkt_len)
> > +		return 0;
> > +
> > +	if (rte_raw_cksum_mbuf(m, l4_off, m->pkt_len - l4_off,
> &raw_cksum))
> > +		return 0;
> > +
> > +	cksum = raw_cksum + rte_ipv6_phdr_cksum(ipv6_hdr, 0);
> > +
> > +	cksum = ((cksum & 0xffff0000) >> 16) + (cksum & 0xffff);
> Same, please check if we can opt for __rte_raw_cksum_reduce(cksum)
> > +
> > +	return (uint16_t)cksum;
> > +}
> > +
> > +/**
> > + * @warning
> > + * @b EXPERIMENTAL: this API may change without prior notice.
> > + *
> > + * Process the IPv6 UDP or TCP checksum of a packet.
> > + *
> > + * The IPv6 header must not be followed by extension headers. The
> > +layer 4
> > + * checksum must be set to 0 in the L4 header by the caller.
> > + *
> > + * @param m
> > + *   The pointer to the mbuf.
> > + * @param ipv6_hdr
> > + *   The pointer to the contiguous IPv6 header.
> > + * @param l4_off
> > + *   The offset in bytes to start L4 checksum.
> > + * @return
> > + *   The complemented checksum to set in the L4 header.
> > + */
> > +__rte_experimental
> > +static inline uint16_t
> > +rte_ipv6_udptcp_cksum_mbuf(const struct rte_mbuf *m,
> > +			   const struct rte_ipv6_hdr *ipv6_hdr, uint16_t l4_off)
> {
> > +	uint16_t cksum = __rte_ipv6_udptcp_cksum_mbuf(m, ipv6_hdr,
> l4_off);
> > +
> > +	cksum = ~cksum;
> > +
> > +	/*
> > +	 * Per RFC 768: If the computed checksum is zero for UDP,
> > +	 * it is transmitted as all ones
> > +	 * (the equivalent in one's complement arithmetic).
> > +	 */
> > +	if (cksum == 0 && ipv6_hdr->proto == IPPROTO_UDP)
> > +		cksum = 0xffff;
> > +
> > +	return cksum;
> > +}
> > +
> >   /**
> >    * Validate the IPv6 UDP or TCP checksum.
> >    *
> > @@ -565,6 +718,39 @@ rte_ipv6_udptcp_cksum_verify(const struct
> rte_ipv6_hdr *ipv6_hdr,
> >   	return 0;
> >   }
> >
> > +/**
> > + * @warning
> > + * @b EXPERIMENTAL: this API may change without prior notice.
> > + *
> > + * Validate the IPv6 UDP or TCP checksum of a packet.
> > + *
> > + * In case of UDP, the caller must first check if udp_hdr->dgram_cksum is 0:
> > + * this is either invalid or means no checksum in some situations.
> > +See 8.1
> > + * (Upper-Layer Checksums) in RFC 8200.
> > + *
> > + * @param m
> > + *   The pointer to the mbuf.
> > + * @param ipv6_hdr
> > + *   The pointer to the contiguous IPv6 header.
> > + * @param l4_off
> > + *   The offset in bytes to start L4 checksum.
> > + * @return
> > + *   Return 0 if the checksum is correct, else -1.
> > + */
> > +__rte_experimental
> > +static inline int
> > +rte_ipv6_udptcp_cksum_mbuf_verify(const struct rte_mbuf *m,
> > +				  const struct rte_ipv6_hdr *ipv6_hdr,
> > +				  uint16_t l4_off)
> > +{
> > +	uint16_t cksum = __rte_ipv6_udptcp_cksum_mbuf(m, ipv6_hdr,
> l4_off);
> > +
> > +	if (cksum != 0xffff)
> > +		return -1;
> > +
> > +	return 0;
> > +}
> > +
> >   /** IPv6 fragment extension header. */
> >   #define	RTE_IPV6_EHDR_MF_SHIFT	0
> >   #define	RTE_IPV6_EHDR_MF_MASK	1
> > diff --git a/lib/net/version.map b/lib/net/version.map index
> > 4f4330d1c4..0f2aacdef8 100644
> > --- a/lib/net/version.map
> > +++ b/lib/net/version.map
> > @@ -12,3 +12,13 @@ DPDK_22 {
> >
> >   	local: *;
> >   };
> > +
> > +EXPERIMENTAL {
> > +	global:
> > +
> > +	# added in 22.03
> > +	rte_ipv4_udptcp_cksum_mbuf;
> > +	rte_ipv4_udptcp_cksum_mbuf_verify;
> > +	rte_ipv6_udptcp_cksum_mbuf;
> > +	rte_ipv6_udptcp_cksum_mbuf_verify;
> > +};