Re: [Qemu-devel] [PATCH V2 2/2] [SLIRP] Delayed IP packets

[Jan Kiszka]

On 2011-07-29 18:25, Fabien Chouteau wrote:
> In the current implementation, if Slirp tries to send an IP packet to a client
> with an unknown hardware address, the packet is simply dropped and an ARP
> request is sent (if_encap in slirp/slirp.c).
> 
> With this patch, Slirp will send the ARP request, re-queue the packet and try
> to send it later. The packet is dropped after one second if the ARP reply is
> not received.
> 
> Signed-off-by: Fabien Chouteau <address@hidden>
> ---
>  slirp/if.c    |   28 ++++++++++++++++++++---
>  slirp/main.h  |    2 +-
>  slirp/mbuf.c  |    2 +
>  slirp/mbuf.h  |    2 +
>  slirp/slirp.c |   67 ++++++++++++++++++++++++++++++--------------------------
>  slirp/slirp.h |   15 ++++++++++++
>  6 files changed, 80 insertions(+), 36 deletions(-)
> 
> diff --git a/slirp/if.c b/slirp/if.c
> index 0f04e13..80a5c4e 100644
> --- a/slirp/if.c
> +++ b/slirp/if.c
> @@ -6,6 +6,7 @@
>   */
>  
>  #include <slirp.h>
> +#include "qemu-timer.h"
>  
>  #define ifs_init(ifm) ((ifm)->ifs_next = (ifm)->ifs_prev = (ifm))
>  
> @@ -105,6 +106,9 @@ if_output(struct socket *so, struct mbuf *ifm)
>       ifs_init(ifm);
>       insque(ifm, ifq);
>  
> +        /* Expiration date = Now + 1 second */
> +        ifm->expiration_date = qemu_get_clock_ns(vm_clock) + 1000000000ULL;

Slirp uses rt_clock for expiry, let's stick with that clock.

> +
>  diddit:
>       slirp->if_queued++;
>  
> @@ -153,6 +157,9 @@ diddit:
>  void
>  if_start(Slirp *slirp)
>  {
> +    int requeued = 0;
> +    uint64_t now;
> +
>       struct mbuf *ifm, *ifqt;
>  
>       DEBUG_CALL("if_start");
> @@ -165,6 +172,8 @@ if_start(Slirp *slirp)
>          if (!slirp_can_output(slirp->opaque))
>              return;
>  
> +        now = qemu_get_clock_ns(vm_clock);
> +
>       /*
>        * See which queue to get next packet from
>        * If there's something in the fastq, select it immediately
> @@ -199,11 +208,22 @@ if_start(Slirp *slirp)
>                  ifm->ifq_so->so_nqueued = 0;
>       }
>  
> -     /* Encapsulate the packet for sending */
> -        if_encap(slirp, (uint8_t *)ifm->m_data, ifm->m_len);
> -
> -        m_free(ifm);
> +        if (ifm->expiration_date < now) {
> +            /* Expired */
> +            m_free(ifm);
> +        } else {
> +            /* Encapsulate the packet for sending */
> +            if (if_encap(slirp, ifm)) {
> +                m_free(ifm);
> +            } else {
> +                /* re-queue */
> +                insque(ifm, ifqt);
> +                requeued++;
> +            }
> +        }
>  
>       if (slirp->if_queued)
>          goto again;
> +
> +        slirp->if_queued = requeued;
>  }
> diff --git a/slirp/main.h b/slirp/main.h
> index 0dd8d81..028df4b 100644
> --- a/slirp/main.h
> +++ b/slirp/main.h
> @@ -42,5 +42,5 @@ extern int tcp_keepintvl;
>  #define PROTO_PPP 0x2
>  #endif
>  
> -void if_encap(Slirp *slirp, const uint8_t *ip_data, int ip_data_len);
> +int if_encap(Slirp *slirp, struct mbuf *ifm);
>  ssize_t slirp_send(struct socket *so, const void *buf, size_t len, int 
> flags);
> diff --git a/slirp/mbuf.c b/slirp/mbuf.c
> index ce2eb84..c699c75 100644
> --- a/slirp/mbuf.c
> +++ b/slirp/mbuf.c
> @@ -70,6 +70,8 @@ m_get(Slirp *slirp)
>       m->m_len = 0;
>          m->m_nextpkt = NULL;
>          m->m_prevpkt = NULL;
> +        m->arp_requested = false;
> +        m->expiration_date = (uint64_t)-1;
>  end_error:
>       DEBUG_ARG("m = %lx", (long )m);
>       return m;
> diff --git a/slirp/mbuf.h b/slirp/mbuf.h
> index b74544b..55170e5 100644
> --- a/slirp/mbuf.h
> +++ b/slirp/mbuf.h
> @@ -86,6 +86,8 @@ struct mbuf {
>               char    m_dat_[1]; /* ANSI don't like 0 sized arrays */
>               char    *m_ext_;
>       } M_dat;
> +    bool     arp_requested;
> +    uint64_t expiration_date;
>  };
>  
>  #define m_next               m_hdr.mh_next
> diff --git a/slirp/slirp.c b/slirp/slirp.c
> index ba76757..b006620 100644
> --- a/slirp/slirp.c
> +++ b/slirp/slirp.c
> @@ -237,6 +237,8 @@ Slirp *slirp_init(int restricted, struct in_addr vnetwork,
>  
>      QTAILQ_INSERT_TAIL(&slirp_instances, slirp, entry);
>  
> +    slirp->delayed = NULL;
> +
>      return slirp;
>  }
>  
> @@ -693,54 +695,57 @@ void slirp_input(Slirp *slirp, const uint8_t *pkt, int 
> pkt_len)
>  }
>  
>  /* output the IP packet to the ethernet device */
> -void if_encap(Slirp *slirp, const uint8_t *ip_data, int ip_data_len)
> +int if_encap(Slirp *slirp, struct mbuf *ifm)
>  {
>      uint8_t buf[1600];
>      struct ethhdr *eh = (struct ethhdr *)buf;
>      uint8_t ethaddr[ETH_ALEN];
> -    const struct ip *iph = (const struct ip *)ip_data;
> +    const struct ip *iph = (const struct ip *)ifm->m_data;
>  
> -    if (ip_data_len + ETH_HLEN > sizeof(buf))
> -        return;
> +    if (ifm->m_len + ETH_HLEN > sizeof(buf))
> +        return 1;

Even if the old cold lacked them as well: { }

>  
>      if (!arp_table_search(&slirp->arp_table, iph->ip_dst.s_addr, ethaddr)) {
>          uint8_t arp_req[ETH_HLEN + sizeof(struct arphdr)];
>          struct ethhdr *reh = (struct ethhdr *)arp_req;
>          struct arphdr *rah = (struct arphdr *)(arp_req + ETH_HLEN);
>  
> -        /* If the client addr is not known, there is no point in
> -           sending the packet to it. Normally the sender should have
> -           done an ARP request to get its MAC address. Here we do it
> -           in place of sending the packet and we hope that the sender
> -           will retry sending its packet. */
> -        memset(reh->h_dest, 0xff, ETH_ALEN);
> -        memcpy(reh->h_source, special_ethaddr, ETH_ALEN - 4);
> -        memcpy(&reh->h_source[2], &slirp->vhost_addr, 4);
> -        reh->h_proto = htons(ETH_P_ARP);
> -        rah->ar_hrd = htons(1);
> -        rah->ar_pro = htons(ETH_P_IP);
> -        rah->ar_hln = ETH_ALEN;
> -        rah->ar_pln = 4;
> -        rah->ar_op = htons(ARPOP_REQUEST);
> -        /* source hw addr */
> -        memcpy(rah->ar_sha, special_ethaddr, ETH_ALEN - 4);
> -        memcpy(&rah->ar_sha[2], &slirp->vhost_addr, 4);
> -        /* source IP */
> -        rah->ar_sip = slirp->vhost_addr.s_addr;
> -        /* target hw addr (none) */
> -        memset(rah->ar_tha, 0, ETH_ALEN);
> -        /* target IP */
> -        rah->ar_tip = iph->ip_dst.s_addr;
> -        slirp->client_ipaddr = iph->ip_dst;
> -        slirp_output(slirp->opaque, arp_req, sizeof(arp_req));
> +        if (!ifm->arp_requested) {
> +

This newline is superfluous...

> +            /* If the client addr is not known, send an ARP request */
> +            memset(reh->h_dest, 0xff, ETH_ALEN);
> +            memcpy(reh->h_source, special_ethaddr, ETH_ALEN - 4);
> +            memcpy(&reh->h_source[2], &slirp->vhost_addr, 4);
> +            reh->h_proto = htons(ETH_P_ARP);
> +            rah->ar_hrd = htons(1);
> +            rah->ar_pro = htons(ETH_P_IP);
> +            rah->ar_hln = ETH_ALEN;
> +            rah->ar_pln = 4;
> +            rah->ar_op = htons(ARPOP_REQUEST);

...while it would improve readability here (and below).

> +            /* source hw addr */
> +            memcpy(rah->ar_sha, special_ethaddr, ETH_ALEN - 4);
> +            memcpy(&rah->ar_sha[2], &slirp->vhost_addr, 4);
> +            /* source IP */
> +            rah->ar_sip = slirp->vhost_addr.s_addr;
> +            /* target hw addr (none) */
> +            memset(rah->ar_tha, 0, ETH_ALEN);
> +            /* target IP */
> +            rah->ar_tip = iph->ip_dst.s_addr;
> +            slirp->client_ipaddr = iph->ip_dst;
> +            slirp_output(slirp->opaque, arp_req, sizeof(arp_req));
> +            ifm->arp_requested = true;
> +        }
> +        return 0;
>      } else {
> +        ifm->arp_requested = false;

Why? If that is required, you would have to make expiry checks depend on
arp_requested as well - or reset the expiry date here.

Jan

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