Re: [Qemu-devel] [PATCHv7 4/9] slirp: Factorizing tcpiphdr structure with an union

[Samuel Thibault <samuel.thibault@gnu.org>]

Hello,

Just to make sure: we have not received comments on this patch.

(that said, it's the most complex part of the series, so I'm not
surprised if it takes more time :) )

Samuel

Samuel Thibault, on Sun 14 Feb 2016 18:47:38 +0100, wrote:
> From: Guillaume Subiron <maethor@subiron.org>
> 
> This patch factorizes the tcpiphdr structure to put the IPv4 fields in
> an union, for addition of version 6 in further patch.
> Using some macros, retrocompatibility of the existing code is assured.
> 
> This patch also fixes the SLIRP_MSIZE and margin computation in various
> functions, and makes them compatible with the new tcpiphdr structure,
> whose size will be bigger than sizeof(struct tcphdr) + sizeof(struct ip)
> 
> Signed-off-by: Guillaume Subiron <maethor@subiron.org>
> Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
> ---
>  slirp/if.h         |  4 ++--
>  slirp/mbuf.c       |  3 ++-
>  slirp/slirp.c      | 15 ++++++++-------
>  slirp/socket.c     | 13 ++++++++++++-
>  slirp/tcp_input.c  | 31 ++++++++++++++++++++-----------
>  slirp/tcp_output.c | 18 +++++++++++++-----
>  slirp/tcp_subr.c   | 31 ++++++++++++++++++++++---------
>  slirp/tcpip.h      | 31 +++++++++++++++++++++++--------
>  8 files changed, 102 insertions(+), 44 deletions(-)
> 
> diff --git a/slirp/if.h b/slirp/if.h
> index 3327023..c7a5c57 100644
> --- a/slirp/if.h
> +++ b/slirp/if.h
> @@ -17,7 +17,7 @@
>  #define IF_MRU 1500
>  #define	IF_COMP IF_AUTOCOMP	/* Flags for compression */
>  
> -/* 2 for alignment, 14 for ethernet, 40 for TCP/IP */
> -#define IF_MAXLINKHDR (2 + 14 + 40)
> +/* 2 for alignment, 14 for ethernet */
> +#define IF_MAXLINKHDR (2 + ETH_HLEN)
>  
>  #endif
> diff --git a/slirp/mbuf.c b/slirp/mbuf.c
> index c959758..f081c69 100644
> --- a/slirp/mbuf.c
> +++ b/slirp/mbuf.c
> @@ -24,7 +24,8 @@
>   * Find a nice value for msize
>   * XXX if_maxlinkhdr already in mtu
>   */
> -#define SLIRP_MSIZE (IF_MTU + IF_MAXLINKHDR + offsetof(struct mbuf, m_dat) + 6)
> +#define SLIRP_MSIZE\
> +    (offsetof(struct mbuf, m_dat) + IF_MAXLINKHDR + TCPIPHDR_DELTA + IF_MTU)
>  
>  void
>  m_init(Slirp *slirp)
> diff --git a/slirp/slirp.c b/slirp/slirp.c
> index 5f42ada..c2c4597 100644
> --- a/slirp/slirp.c
> +++ b/slirp/slirp.c
> @@ -754,15 +754,16 @@ void slirp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
>          m = m_get(slirp);
>          if (!m)
>              return;
> -        /* Note: we add to align the IP header */
> -        if (M_FREEROOM(m) < pkt_len + 2) {
> -            m_inc(m, pkt_len + 2);
> +        /* Note: we add 2 to align the IP header on 4 bytes,
> +         * and add the margin for the tcpiphdr overhead  */
> +        if (M_FREEROOM(m) < pkt_len + TCPIPHDR_DELTA + 2) {
> +            m_inc(m, pkt_len + TCPIPHDR_DELTA + 2);
>          }
> -        m->m_len = pkt_len + 2;
> -        memcpy(m->m_data + 2, pkt, pkt_len);
> +        m->m_len = pkt_len + TCPIPHDR_DELTA + 2;
> +        memcpy(m->m_data + TCPIPHDR_DELTA + 2, pkt, pkt_len);
>  
> -        m->m_data += 2 + ETH_HLEN;
> -        m->m_len -= 2 + ETH_HLEN;
> +        m->m_data += TCPIPHDR_DELTA + 2 + ETH_HLEN;
> +        m->m_len -= TCPIPHDR_DELTA + 2 + ETH_HLEN;
>  
>          if (proto == ETH_P_IP) {
>              ip_input(m);
> diff --git a/slirp/socket.c b/slirp/socket.c
> index b79ddec..d4b02c8 100644
> --- a/slirp/socket.c
> +++ b/slirp/socket.c
> @@ -483,7 +483,18 @@ sorecvfrom(struct socket *so)
>  	  if (!m) {
>  	      return;
>  	  }
> -	  m->m_data += IF_MAXLINKHDR;
> +	  switch (so->so_ffamily) {
> +	  case AF_INET:
> +	      m->m_data += IF_MAXLINKHDR + sizeof(struct udpiphdr);
> +	      break;
> +	  case AF_INET6:
> +	      m->m_data += IF_MAXLINKHDR + sizeof(struct ip6)
> +	                                 + sizeof(struct udphdr);
> +	      break;
> +	  default:
> +	      g_assert_not_reached();
> +	      break;
> +	  }
>  
>  	  /*
>  	   * XXX Shouldn't FIONREAD packets destined for port 53,
> diff --git a/slirp/tcp_input.c b/slirp/tcp_input.c
> index 5f845da..26b0c8b 100644
> --- a/slirp/tcp_input.c
> +++ b/slirp/tcp_input.c
> @@ -256,11 +256,6 @@ tcp_input(struct mbuf *m, int iphlen, struct socket *inso)
>  	}
>  	slirp = m->slirp;
>  
> -	/*
> -	 * Get IP and TCP header together in first mbuf.
> -	 * Note: IP leaves IP header in first mbuf.
> -	 */
> -	ti = mtod(m, struct tcpiphdr *);
>  	if (iphlen > sizeof(struct ip )) {
>  	  ip_stripoptions(m, (struct mbuf *)0);
>  	  iphlen=sizeof(struct ip );
> @@ -277,14 +272,28 @@ tcp_input(struct mbuf *m, int iphlen, struct socket *inso)
>  	save_ip.ip_len+= iphlen;
>  
>  	/*
> +	 * Get IP and TCP header together in first mbuf.
> +	 * Note: IP leaves IP header in first mbuf.
> +	 */
> +	m->m_data -= sizeof(struct tcpiphdr) - (sizeof(struct ip)
> +	                                     + sizeof(struct tcphdr));
> +	m->m_len += sizeof(struct tcpiphdr) - (sizeof(struct ip)
> +	                                    + sizeof(struct tcphdr));
> +	ti = mtod(m, struct tcpiphdr *);
> +
> +	/*
>  	 * Checksum extended TCP header and data.
>  	 */
> -	tlen = ((struct ip *)ti)->ip_len;
> -        tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL;
> -        memset(&ti->ti_i.ih_mbuf, 0 , sizeof(struct mbuf_ptr));
> -	ti->ti_x1 = 0;
> +	tlen = ip->ip_len;
> +	tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL;
> +	memset(&ti->ih_mbuf, 0 , sizeof(struct mbuf_ptr));
> +	memset(&ti->ti, 0, sizeof(ti->ti));
> +	ti->ti_x0 = 0;
> +	ti->ti_src = save_ip.ip_src;
> +	ti->ti_dst = save_ip.ip_dst;
> +	ti->ti_pr = save_ip.ip_p;
>  	ti->ti_len = htons((uint16_t)tlen);
> -	len = sizeof(struct ip ) + tlen;
> +	len = ((sizeof(struct tcpiphdr) - sizeof(struct tcphdr)) + tlen);
>  	if(cksum(m, len)) {
>  	  goto drop;
>  	}
> @@ -1475,7 +1484,7 @@ tcp_mss(struct tcpcb *tp, u_int offer)
>  	DEBUG_ARG("tp = %p", tp);
>  	DEBUG_ARG("offer = %d", offer);
>  
> -	mss = min(IF_MTU, IF_MRU) - sizeof(struct tcpiphdr);
> +	mss = min(IF_MTU, IF_MRU) - sizeof(struct tcphdr) + sizeof(struct ip);
>  	if (offer)
>  		mss = min(mss, offer);
>  	mss = max(mss, 32);
> diff --git a/slirp/tcp_output.c b/slirp/tcp_output.c
> index 34e4d2e..7fc6a87 100644
> --- a/slirp/tcp_output.c
> +++ b/slirp/tcp_output.c
> @@ -448,15 +448,23 @@ send:
>  	 */
>  	m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */
>  
> -    {
> +	struct tcpiphdr tcpiph_save = *(mtod(m, struct tcpiphdr *));
> +	m->m_data += sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
> +	                                     - sizeof(struct ip);
> +	m->m_len  -= sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
> +	                                     - sizeof(struct ip);
> +	struct ip *ip = mtod(m, struct ip *);
>  
> -	((struct ip *)ti)->ip_len = m->m_len;
> +	ip->ip_len = m->m_len;
> +	ip->ip_dst = tcpiph_save.ti_dst;
> +	ip->ip_src = tcpiph_save.ti_src;
> +	ip->ip_p = tcpiph_save.ti_pr;
>  
> -	((struct ip *)ti)->ip_ttl = IPDEFTTL;
> -	((struct ip *)ti)->ip_tos = so->so_iptos;
> +	ip->ip_ttl = IPDEFTTL;
> +	ip->ip_tos = so->so_iptos;
>  
>  	error = ip_output(so, m);
> -    }
> +
>  	if (error) {
>  out:
>  		return (error);
> diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c
> index b1aa1f2..cd021df 100644
> --- a/slirp/tcp_subr.c
> +++ b/slirp/tcp_subr.c
> @@ -76,9 +76,10 @@ tcp_template(struct tcpcb *tp)
>  	register struct tcpiphdr *n = &tp->t_template;
>  
>  	n->ti_mbuf = NULL;
> -	n->ti_x1 = 0;
> +	memset(&n->ti, 0, sizeof(n->ti));
> +	n->ti_x0 = 0;
>  	n->ti_pr = IPPROTO_TCP;
> -	n->ti_len = htons(sizeof (struct tcpiphdr) - sizeof (struct ip));
> +	n->ti_len = htons(sizeof(struct tcphdr));
>  	n->ti_src = so->so_faddr;
>  	n->ti_dst = so->so_laddr;
>  	n->ti_sport = so->so_fport;
> @@ -131,6 +132,7 @@ tcp_respond(struct tcpcb *tp, struct tcpiphdr *ti, struct mbuf *m,
>  		m->m_data += IF_MAXLINKHDR;
>  		*mtod(m, struct tcpiphdr *) = *ti;
>  		ti = mtod(m, struct tcpiphdr *);
> +		memset(&ti->ti, 0, sizeof(ti->ti));
>  		flags = TH_ACK;
>  	} else {
>  		/*
> @@ -150,8 +152,8 @@ tcp_respond(struct tcpcb *tp, struct tcpiphdr *ti, struct mbuf *m,
>  	tlen += sizeof (struct tcpiphdr);
>  	m->m_len = tlen;
>  
> -        ti->ti_mbuf = NULL;
> -	ti->ti_x1 = 0;
> +	ti->ti_mbuf = NULL;
> +	ti->ti_x0 = 0;
>  	ti->ti_seq = htonl(seq);
>  	ti->ti_ack = htonl(ack);
>  	ti->ti_x2 = 0;
> @@ -164,12 +166,23 @@ tcp_respond(struct tcpcb *tp, struct tcpiphdr *ti, struct mbuf *m,
>  	ti->ti_urp = 0;
>  	ti->ti_sum = 0;
>  	ti->ti_sum = cksum(m, tlen);
> -	((struct ip *)ti)->ip_len = tlen;
>  
> -	if(flags & TH_RST)
> -	  ((struct ip *)ti)->ip_ttl = MAXTTL;
> -	else
> -	  ((struct ip *)ti)->ip_ttl = IPDEFTTL;
> +	struct tcpiphdr tcpiph_save = *(mtod(m, struct tcpiphdr *));
> +	m->m_data += sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
> +	                                     - sizeof(struct ip);
> +	m->m_len  -= sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
> +	                                     - sizeof(struct ip);
> +	struct ip *ip = mtod(m, struct ip *);
> +	ip->ip_len = tlen;
> +	ip->ip_dst = tcpiph_save.ti_dst;
> +	ip->ip_src = tcpiph_save.ti_src;
> +	ip->ip_p = tcpiph_save.ti_pr;
> +
> +	if (flags & TH_RST) {
> +		ip->ip_ttl = MAXTTL;
> +	} else {
> +		ip->ip_ttl = IPDEFTTL;
> +	}
>  
>  	(void) ip_output((struct socket *)0, m);
>  }
> diff --git a/slirp/tcpip.h b/slirp/tcpip.h
> index 7974ce3..3c5d127 100644
> --- a/slirp/tcpip.h
> +++ b/slirp/tcpip.h
> @@ -37,15 +37,23 @@
>   * Tcp+ip header, after ip options removed.
>   */
>  struct tcpiphdr {
> -	struct 	ipovly ti_i;		/* overlaid ip structure */
> -	struct	tcphdr ti_t;		/* tcp header */
> +    struct mbuf_ptr ih_mbuf;	/* backpointer to mbuf */
> +    union {
> +        struct {
> +            struct  in_addr ih_src; /* source internet address */
> +            struct  in_addr ih_dst; /* destination internet address */
> +            uint8_t ih_x1;          /* (unused) */
> +            uint8_t ih_pr;          /* protocol */
> +        } ti_i4;
> +    } ti;
> +    uint16_t    ti_x0;
> +    uint16_t    ti_len;             /* protocol length */
> +    struct      tcphdr ti_t;        /* tcp header */
>  };
> -#define	ti_mbuf		ti_i.ih_mbuf.mptr
> -#define	ti_x1		ti_i.ih_x1
> -#define	ti_pr		ti_i.ih_pr
> -#define	ti_len		ti_i.ih_len
> -#define	ti_src		ti_i.ih_src
> -#define	ti_dst		ti_i.ih_dst
> +#define	ti_mbuf		ih_mbuf.mptr
> +#define	ti_pr		ti.ti_i4.ih_pr
> +#define	ti_src		ti.ti_i4.ih_src
> +#define	ti_dst		ti.ti_i4.ih_dst
>  #define	ti_sport	ti_t.th_sport
>  #define	ti_dport	ti_t.th_dport
>  #define	ti_seq		ti_t.th_seq
> @@ -65,6 +73,13 @@ struct tcpiphdr {
>  #define tcpfrag_list_end(F, T) (tcpiphdr2qlink(F) == (struct qlink*)(T))
>  #define tcpfrag_list_empty(T) ((T)->seg_next == (struct tcpiphdr*)(T))
>  
> +/* This is the difference between the size of a tcpiphdr structure, and the
> + * size of actual ip+tcp headers, rounded up since we need to align data.  */
> +#define TCPIPHDR_DELTA\
> +    (max(0,\
> +         (sizeof(struct tcpiphdr)\
> +          - sizeof(struct ip) - sizeof(struct tcphdr) + 3) & ~3))
> +
>  /*
>   * Just a clean way to get to the first byte
>   * of the packet
> -- 
> 2.7.0
> 
> 

-- 
Samuel
> X..., c'est un millefeuille avec une couche de crème patissière, une
> de sauce tomate et une de crème d'anchois... Mais c'est vrai que
> c'est un système ouvert: tu peux y rajouter des pépites de chocolat...
-+- Ol in Guide du linuxien pervers - "Remettez m'en une couche !" -+-