Re: [PATCH 06/24] ip: move duplicate IPv4 checksum function to ip.h

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Feb 07, 2024 at 11:40:40AM +0100, Stefano Brivio wrote:
> On Fri,  2 Feb 2024 15:11:33 +0100
> Laurent Vivier <lvivier@redhat.com> wrote:
> 
> > We can find the same function to compute the IPv4 header
> > checksum in tcp.c and udp.c
> > 
> > Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> > ---
> >  ip.h  | 14 ++++++++++++++
> >  tcp.c | 23 ++---------------------
> >  udp.c | 19 +------------------
> >  3 files changed, 17 insertions(+), 39 deletions(-)
> > 
> > diff --git a/ip.h b/ip.h
> > index b2e08bc049f3..ff7902c45a95 100644
> > --- a/ip.h
> > +++ b/ip.h
> > @@ -9,6 +9,8 @@
> >  #include <netinet/ip.h>
> >  #include <netinet/ip6.h>
> >  
> > +#include "checksum.h"
> > +
> >  #define IN4_IS_ADDR_UNSPECIFIED(a) \
> >  	((a)->s_addr == htonl_constant(INADDR_ANY))
> >  #define IN4_IS_ADDR_BROADCAST(a) \
> > @@ -83,4 +85,16 @@ struct ipv6_opt_hdr {
> >  
> >  char *ipv6_l4hdr(const struct pool *p, int idx, size_t offset, uint8_t *proto,
> >  		 size_t *dlen);
> > +static inline uint16_t ipv4_hdr_checksum(struct iphdr *iph, int proto)
> 
> A function comment would be nice. A couple of doubts:
> 
> - why is this an inline in ip.h, instead of a function in checksum.c?
>   That would be more natural, I think
> 
> - this would be the first Layer-4 protocol number passed as int: we use
>   uint8_t elsewhere. Now, socket(2) and similar all take an int, but
>   using uint8_t internally keeps large arrays such as tap4_l4 a bit
>   smaller.
> 
>   The only value defined in Linux UAPI exceeding eight bits is
>   IPPROTO_MPTCP, 262, because that's never on the wire (the TCP
>   protocol number is used instead). And we won't meet that either.

Right.  This is pretty much explicitly the IP protocol number, which
is an 8-bit field in the IPv4 header.

>   In practice, it doesn't matter what we use here, but still uint8_t
>   would be consistent.
> 
> > +{
> > +	uint32_t sum = L2_BUF_IP4_PSUM(proto);
> > +
> > +	sum += iph->tot_len;
> > +	sum += (iph->saddr >> 16) & 0xffff;
> > +	sum += iph->saddr & 0xffff;
> > +	sum += (iph->daddr >> 16) & 0xffff;
> > +	sum += iph->daddr & 0xffff;
> > +
> > +	return ~csum_fold(sum);
> > +}
> >  #endif /* IP_H */
> > diff --git a/tcp.c b/tcp.c
> > index 4c9c5fb51c60..293ab12d8c21 100644
> > --- a/tcp.c
> > +++ b/tcp.c
> > @@ -934,23 +934,6 @@ static void tcp_sock_set_bufsize(const struct ctx *c, int s)
> >  		trace("TCP: failed to set SO_SNDBUF to %i", v);
> >  }
> >  
> > -/**
> > - * tcp_update_check_ip4() - Update IPv4 with variable parts from stored one
> > - * @buf:	L2 packet buffer with final IPv4 header
> > - */
> > -static void tcp_update_check_ip4(struct tcp4_l2_buf_t *buf)
> > -{
> > -	uint32_t sum = L2_BUF_IP4_PSUM(IPPROTO_TCP);
> > -
> > -	sum += buf->iph.tot_len;
> > -	sum += (buf->iph.saddr >> 16) & 0xffff;
> > -	sum += buf->iph.saddr & 0xffff;
> > -	sum += (buf->iph.daddr >> 16) & 0xffff;
> > -	sum += buf->iph.daddr & 0xffff;
> > -
> > -	buf->iph.check = (uint16_t)~csum_fold(sum);
> > -}
> > -
> >  /**
> >   * tcp_update_check_tcp4() - Update TCP checksum from stored one
> >   * @buf:	L2 packet buffer with final IPv4 header
> > @@ -1393,10 +1376,8 @@ do {									\
> >  		b->iph.saddr = a4->s_addr;
> >  		b->iph.daddr = c->ip4.addr_seen.s_addr;
> >  
> > -		if (check)
> > -			b->iph.check = *check;
> > -		else
> > -			tcp_update_check_ip4(b);
> > +		b->iph.check = check ? *check :
> > +				       ipv4_hdr_checksum(&b->iph, IPPROTO_TCP);
> >  
> >  		SET_TCP_HEADER_COMMON_V4_V6(b, conn, seq);
> >  
> > diff --git a/udp.c b/udp.c
> > index d514c864ab5b..6f867df81c05 100644
> > --- a/udp.c
> > +++ b/udp.c
> > @@ -270,23 +270,6 @@ static void udp_invert_portmap(struct udp_port_fwd *fwd)
> >  	}
> >  }
> >  
> > -/**
> > - * udp_update_check4() - Update checksum with variable parts from stored one
> > - * @buf:	L2 packet buffer with final IPv4 header
> > - */
> > -static void udp_update_check4(struct udp4_l2_buf_t *buf)
> > -{
> > -	uint32_t sum = L2_BUF_IP4_PSUM(IPPROTO_UDP);
> > -
> > -	sum += buf->iph.tot_len;
> > -	sum += (buf->iph.saddr >> 16) & 0xffff;
> > -	sum += buf->iph.saddr & 0xffff;
> > -	sum += (buf->iph.daddr >> 16) & 0xffff;
> > -	sum += buf->iph.daddr & 0xffff;
> > -
> > -	buf->iph.check = (uint16_t)~csum_fold(sum);
> > -}
> > -
> >  /**
> >   * udp_update_l2_buf() - Update L2 buffers with Ethernet and IPv4 addresses
> >   * @eth_d:	Ethernet destination address, NULL if unchanged
> > @@ -614,7 +597,7 @@ static size_t udp_update_hdr4(const struct ctx *c, int n, in_port_t dstport,
> >  		b->iph.saddr = b->s_in.sin_addr.s_addr;
> >  	}
> >  
> > -	udp_update_check4(b);
> > +	b->iph.check = ipv4_hdr_checksum(&b->iph, IPPROTO_UDP);
> >  	b->uh.source = b->s_in.sin_port;
> >  	b->uh.dest = htons(dstport);
> >  	b->uh.len = htons(udp4_l2_mh_sock[n].msg_len + sizeof(b->uh));
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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