Re: [Qemu-devel] [PATCH 1/2] [SLIRP] Simple ARP table

[Jan Kiszka]

On 2011-07-26 18:21, Fabien Chouteau wrote:
> This patch adds a simple ARP table in Slirp and also adds handling of
> gratuitous ARP requests.
> 
> Signed-off-by: Fabien Chouteau <address@hidden>
> ---
>  Makefile.objs     |    2 +-
>  slirp/arp_table.c |   61 +++++++++++++++++++++++++++++++++++++++++++++++
>  slirp/bootp.c     |   15 ++++++-----
>  slirp/slirp.c     |   68 ++++++++++++++++------------------------------------
>  slirp/slirp.h     |   51 +++++++++++++++++++++++++++++++++++++--
>  5 files changed, 139 insertions(+), 58 deletions(-)
>  create mode 100644 slirp/arp_table.c
> 
> diff --git a/Makefile.objs b/Makefile.objs
> index 6991a9f..0c10557 100644
> --- a/Makefile.objs
> +++ b/Makefile.objs
> @@ -151,7 +151,7 @@ common-obj-y += qemu-timer.o qemu-timer-common.o
> 
>  slirp-obj-y = cksum.o if.o ip_icmp.o ip_input.o ip_output.o
>  slirp-obj-y += slirp.o mbuf.o misc.o sbuf.o socket.o tcp_input.o tcp_output.o
> -slirp-obj-y += tcp_subr.o tcp_timer.o udp.o bootp.o tftp.o
> +slirp-obj-y += tcp_subr.o tcp_timer.o udp.o bootp.o tftp.o arp_table.o
>  common-obj-$(CONFIG_SLIRP) += $(addprefix slirp/, $(slirp-obj-y))
> 
>  # xen backend driver support
> diff --git a/slirp/arp_table.c b/slirp/arp_table.c
> new file mode 100644
> index 0000000..e3251ed
> --- /dev/null
> +++ b/slirp/arp_table.c
> @@ -0,0 +1,61 @@
> +#include "slirp.h"
> +
> +void arp_table_flush(ArpTable *arptbl)
> +{
> +    int i;
> +
> +    assert(arptbl != NULL);
> +
> +    for (i = 0; i < ARP_TABLE_SIZE; i++) {
> +        arptbl->table[i].ar_sip = 0;
> +    }
> +    arptbl->next_victim = 0;
> +}

arp_table_flush is only used for initialization, but the memory it
touches is already zero-initialized (on alloc in slirp_init). So you can
save this service.

> +
> +void arp_table_add(ArpTable      *arptbl,
> +                   struct arphdr *ahdr)

Let's stick with

void arp_table_add(ArpTable *arptbl, struct arphdr *ahdr)

formatting. That's more consistent with other parts of QEMU.

> +{
> +    int i;
> +
> +    DEBUG_CALL("arp_table_add");
> +    DEBUG_ARG("ip = 0x%x", ahdr->ar_sip);
> +    DEBUG_ARGS((dfd, " hw addr = %02x:%02x:%02x:%02x:%02x:%02x\n",
> +                ahdr->ar_sha[0], ahdr->ar_sha[1], ahdr->ar_sha[2],
> +                ahdr->ar_sha[3], ahdr->ar_sha[4], ahdr->ar_sha[5]));
> +
> +    /* Search for an entry */
> +    for (i = 0; i < ARP_TABLE_SIZE && arptbl->table[i].ar_sip != 0; i++) {
> +        if (arptbl->table[i].ar_sip == ahdr->ar_sip) {
> +            /* Update the entry */
> +            memcpy(arptbl->table[i].ar_sha,  ahdr->ar_sha, ETH_ALEN);
> +            return;
> +        }
> +    }
> +
> +    /* No entry found, create a new one */
> +    arptbl->table[arptbl->next_victim].ar_sip = ahdr->ar_sip;
> +    memcpy(arptbl->table[arptbl->next_victim].ar_sha,  ahdr->ar_sha, 
> ETH_ALEN);
> +    arptbl->next_victim = (arptbl->next_victim + 1) % ARP_TABLE_SIZE;

Pragmatic aging. But I guess that's OK, we shouldn't need anything
smarter here.

> +}
> +
> +bool arp_table_search(ArpTable *arptbl,
> +                      int       in_ip_addr,
> +                      uint8_t   out_ethaddr[ETH_ALEN])
> +{
> +    int i;
> +
> +    DEBUG_CALL("arp_table_search");
> +    DEBUG_ARG("ip = 0x%x", in_ip_addr);
> +
> +    for (i = 0; i < ARP_TABLE_SIZE; i++) {
> +        if (arptbl->table[i].ar_sip == in_ip_addr) {
> +            memcpy(out_ethaddr, arptbl->table[i].ar_sha,  ETH_ALEN);
> +            DEBUG_ARGS((dfd, " found hw addr = 
> %02x:%02x:%02x:%02x:%02x:%02x\n",
> +                        out_ethaddr[0], out_ethaddr[1], out_ethaddr[2],
> +                        out_ethaddr[3], out_ethaddr[4], out_ethaddr[5]));
> +            return 1;
> +        }
> +    }
> +
> +    return 0;
> +}
> diff --git a/slirp/bootp.c b/slirp/bootp.c
> index 1eb2ed1..ccca93b 100644
> --- a/slirp/bootp.c
> +++ b/slirp/bootp.c
> @@ -149,6 +149,7 @@ static void bootp_reply(Slirp *slirp, const struct 
> bootp_t *bp)
>      struct in_addr preq_addr;
>      int dhcp_msg_type, val;
>      uint8_t *q;
> +    uint8_t client_ethaddr[ETH_ALEN];
> 
>      /* extract exact DHCP msg type */
>      dhcp_decode(bp, &dhcp_msg_type, &preq_addr);
> @@ -165,7 +166,7 @@ static void bootp_reply(Slirp *slirp, const struct 
> bootp_t *bp)
>          dhcp_msg_type != DHCPREQUEST)
>          return;
>      /* XXX: this is a hack to get the client mac address */
> -    memcpy(slirp->client_ethaddr, bp->bp_hwaddr, 6);
> +    memcpy(client_ethaddr, bp->bp_hwaddr, ETH_ALEN);

Makes me wonder if the comment above still applies.

> 
>      m = m_get(slirp);
>      if (!m) {
> @@ -178,25 +179,25 @@ static void bootp_reply(Slirp *slirp, const struct 
> bootp_t *bp)
> 
>      if (dhcp_msg_type == DHCPDISCOVER) {
>          if (preq_addr.s_addr != htonl(0L)) {
> -            bc = request_addr(slirp, &preq_addr, slirp->client_ethaddr);
> +            bc = request_addr(slirp, &preq_addr, client_ethaddr);
>              if (bc) {
>                  daddr.sin_addr = preq_addr;
>              }
>          }
>          if (!bc) {
>           new_addr:
> -            bc = get_new_addr(slirp, &daddr.sin_addr, slirp->client_ethaddr);
> +            bc = get_new_addr(slirp, &daddr.sin_addr, client_ethaddr);
>              if (!bc) {
>                  DPRINTF("no address left\n");
>                  return;
>              }
>          }
> -        memcpy(bc->macaddr, slirp->client_ethaddr, 6);
> +        memcpy(bc->macaddr, client_ethaddr, ETH_ALEN);
>      } else if (preq_addr.s_addr != htonl(0L)) {
> -        bc = request_addr(slirp, &preq_addr, slirp->client_ethaddr);
> +        bc = request_addr(slirp, &preq_addr, client_ethaddr);
>          if (bc) {
>              daddr.sin_addr = preq_addr;
> -            memcpy(bc->macaddr, slirp->client_ethaddr, 6);
> +            memcpy(bc->macaddr, client_ethaddr, ETH_ALEN);
>          } else {
>              daddr.sin_addr.s_addr = 0;
>          }
> @@ -218,7 +219,7 @@ static void bootp_reply(Slirp *slirp, const struct 
> bootp_t *bp)
>      rbp->bp_xid = bp->bp_xid;
>      rbp->bp_htype = 1;
>      rbp->bp_hlen = 6;
> -    memcpy(rbp->bp_hwaddr, bp->bp_hwaddr, 6);
> +    memcpy(rbp->bp_hwaddr, bp->bp_hwaddr, ETH_ALEN);
> 
>      rbp->bp_yiaddr = daddr.sin_addr; /* Client IP address */
>      rbp->bp_siaddr = saddr.sin_addr; /* Server IP address */
> diff --git a/slirp/slirp.c b/slirp/slirp.c
> index df787ea..29966e6 100644
> --- a/slirp/slirp.c
> +++ b/slirp/slirp.c
> @@ -31,11 +31,11 @@
>  struct in_addr loopback_addr;
> 
>  /* emulated hosts use the MAC addr 52:55:IP:IP:IP:IP */
> -static const uint8_t special_ethaddr[6] = {
> +static const uint8_t special_ethaddr[ETH_ALEN] = {
>      0x52, 0x55, 0x00, 0x00, 0x00, 0x00
>  };
> 
> -static const uint8_t zero_ethaddr[6] = { 0, 0, 0, 0, 0, 0 };
> +static const uint8_t zero_ethaddr[ETH_ALEN] = { 0, 0, 0, 0, 0, 0 };
> 
>  /* XXX: suppress those select globals */
>  fd_set *global_readfds, *global_writefds, *global_xfds;
> @@ -237,6 +237,8 @@ Slirp *slirp_init(int restricted, struct in_addr vnetwork,
> 
>      QTAILQ_INSERT_TAIL(&slirp_instances, slirp, entry);
> 
> +    arp_table_flush(&slirp->arp_table);
> +
>      return slirp;
>  }
> 
> @@ -599,42 +601,8 @@ void slirp_select_poll(fd_set *readfds, fd_set 
> *writefds, fd_set *xfds,
>          global_xfds = NULL;
>  }
> 
> -#define ETH_ALEN 6
> -#define ETH_HLEN 14
> -
> -#define ETH_P_IP       0x0800          /* Internet Protocol packet     */
> -#define ETH_P_ARP      0x0806          /* Address Resolution packet    */
> -
> -#define        ARPOP_REQUEST   1               /* ARP request                
>   */
> -#define        ARPOP_REPLY     2               /* ARP reply                  
>   */
> -
> -struct ethhdr
> -{
> -       unsigned char   h_dest[ETH_ALEN];       /* destination eth addr */
> -       unsigned char   h_source[ETH_ALEN];     /* source ether addr    */
> -       unsigned short  h_proto;                /* packet type ID field */
> -};
> -
> -struct arphdr
> -{
> -       unsigned short  ar_hrd;         /* format of hardware address   */
> -       unsigned short  ar_pro;         /* format of protocol address   */
> -       unsigned char   ar_hln;         /* length of hardware address   */
> -       unsigned char   ar_pln;         /* length of protocol address   */
> -       unsigned short  ar_op;          /* ARP opcode (command)         */
> -
> -        /*
> -         *      Ethernet looks like this : This bit is variable sized 
> however...
> -         */
> -       unsigned char           ar_sha[ETH_ALEN];       /* sender hardware 
> address      */
> -       uint32_t                ar_sip;                 /* sender IP address  
>           */
> -       unsigned char           ar_tha[ETH_ALEN];       /* target hardware 
> address      */
> -       uint32_t                ar_tip  ;               /* target IP address  
>           */
> -} __attribute__((packed));
> -
>  static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
>  {
> -    struct ethhdr *eh = (struct ethhdr *)pkt;
>      struct arphdr *ah = (struct arphdr *)(pkt + ETH_HLEN);
>      uint8_t arp_reply[max(ETH_HLEN + sizeof(struct arphdr), 64)];
>      struct ethhdr *reh = (struct ethhdr *)arp_reply;
> @@ -645,6 +613,13 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, 
> int pkt_len)
>      ar_op = ntohs(ah->ar_op);
>      switch(ar_op) {
>      case ARPOP_REQUEST:
> +

Please drop this blank line.

> +        if (ah->ar_tip == ah->ar_sip) {
> +            /* Gratuitous ARP */
> +            arp_table_add(&slirp->arp_table, ah);
> +            return;
> +        }
> +
>          if ((ah->ar_tip & slirp->vnetwork_mask.s_addr) ==
>              slirp->vnetwork_addr.s_addr) {
>              if (ah->ar_tip == slirp->vnameserver_addr.s_addr ||
> @@ -657,8 +632,7 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, 
> int pkt_len)
>              return;
>          arp_ok:
>              memset(arp_reply, 0, sizeof(arp_reply));
> -            /* XXX: make an ARP request to have the client address */
> -            memcpy(slirp->client_ethaddr, eh->h_source, ETH_ALEN);
> +            arp_table_add(&slirp->arp_table, ah);
> 
>              /* ARP request for alias/dns mac address */
>              memcpy(reh->h_dest, pkt + ETH_ALEN, ETH_ALEN);
> @@ -677,13 +651,11 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, 
> int pkt_len)
>              rah->ar_tip = ah->ar_sip;
>              slirp_output(slirp->opaque, arp_reply, sizeof(arp_reply));
>          }
> +
> +

Spurious empty lines.

>          break;
>      case ARPOP_REPLY:
> -        /* reply to request of client mac address ? */
> -        if (!memcmp(slirp->client_ethaddr, zero_ethaddr, ETH_ALEN) &&
> -            ah->ar_sip == slirp->client_ipaddr.s_addr) {
> -            memcpy(slirp->client_ethaddr, ah->ar_sha, ETH_ALEN);
> -        }
> +        arp_table_add(&slirp->arp_table, ah);
>          break;
>      default:
>          break;
> @@ -729,15 +701,16 @@ void if_encap(Slirp *slirp, const uint8_t *ip_data, int 
> ip_data_len)
>  {
>      uint8_t buf[1600];
>      struct ethhdr *eh = (struct ethhdr *)buf;
> +    uint8_t ethaddr[ETH_ALEN];
> +    const struct ip *iph = (const struct ip *)ip_data;
> 
>      if (ip_data_len + ETH_HLEN > sizeof(buf))
>          return;
> -
> -    if (!memcmp(slirp->client_ethaddr, zero_ethaddr, ETH_ALEN)) {
> +
> +    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);
> -        const struct ip *iph = (const struct ip *)ip_data;
> 
>          /* If the client addr is not known, there is no point in
>             sending the packet to it. Normally the sender should have
> @@ -764,8 +737,9 @@ void if_encap(Slirp *slirp, const uint8_t *ip_data, int 
> ip_data_len)
>          rah->ar_tip = iph->ip_dst.s_addr;
>          slirp->client_ipaddr = iph->ip_dst;
>          slirp_output(slirp->opaque, arp_req, sizeof(arp_req));
> +

...and another one.

>      } else {
> -        memcpy(eh->h_dest, slirp->client_ethaddr, ETH_ALEN);
> +        memcpy(eh->h_dest, ethaddr, ETH_ALEN);
>          memcpy(eh->h_source, special_ethaddr, ETH_ALEN - 4);
>          /* XXX: not correct */
>          memcpy(&eh->h_source[2], &slirp->vhost_addr, 4);
> diff --git a/slirp/slirp.h b/slirp/slirp.h
> index 16bb6ba..13d7471 100644
> --- a/slirp/slirp.h
> +++ b/slirp/slirp.h
> @@ -170,6 +170,52 @@ int inet_aton(const char *cp, struct in_addr *ia);
>  /* osdep.c */
>  int qemu_socket(int domain, int type, int protocol);
> 
> +#define ETH_ALEN 6
> +#define ETH_HLEN 14
> +
> +#define ETH_P_IP  0x0800        /* Internet Protocol packet  */
> +#define ETH_P_ARP 0x0806        /* Address Resolution packet */
> +
> +#define ARPOP_REQUEST 1         /* ARP request */
> +#define ARPOP_REPLY   2         /* ARP reply   */
> +
> +struct ethhdr {
> +    unsigned char  h_dest[ETH_ALEN];   /* destination eth addr */
> +    unsigned char  h_source[ETH_ALEN]; /* source ether addr    */
> +    unsigned short h_proto;            /* packet type ID field */
> +};
> +
> +struct arphdr {
> +    unsigned short ar_hrd;      /* format of hardware address */
> +    unsigned short ar_pro;      /* format of protocol address */
> +    unsigned char  ar_hln;      /* length of hardware address */
> +    unsigned char  ar_pln;      /* length of protocol address */
> +    unsigned short ar_op;       /* ARP opcode (command)       */
> +
> +    /*
> +     *  Ethernet looks like this : This bit is variable sized however...
> +     */
> +    unsigned char ar_sha[ETH_ALEN]; /* sender hardware address */
> +    uint32_t      ar_sip;           /* sender IP address       */
> +    unsigned char ar_tha[ETH_ALEN]; /* target hardware address */
> +    uint32_t      ar_tip;           /* target IP address       */
> +} __attribute__((packed));
> +
> +#define ARP_TABLE_SIZE 16
> +
> +typedef struct ArpTable {
> +    struct arphdr table[ARP_TABLE_SIZE];
> +    int next_victim;
> +} ArpTable;
> +
> +void arp_table_flush(ArpTable *arptbl);
> +
> +void arp_table_add(ArpTable      *arptbl,
> +                   struct arphdr *ahdr);
> +
> +bool arp_table_search(ArpTable *arptbl,
> +                      int       in_ip_addr,
> +                      uint8_t out_ethaddr[ETH_ALEN]);
> 
>  struct Slirp {
>      QTAILQ_ENTRY(Slirp) entry;
> @@ -181,9 +227,6 @@ struct Slirp {
>      struct in_addr vdhcp_startaddr;
>      struct in_addr vnameserver_addr;
> 
> -    /* ARP cache for the guest IP addresses (XXX: allow many entries) */
> -    uint8_t client_ethaddr[6];
> -
>      struct in_addr client_ipaddr;
>      char client_hostname[33];
> 
> @@ -227,6 +270,8 @@ struct Slirp {
>      char *tftp_prefix;
>      struct tftp_session tftp_sessions[TFTP_SESSIONS_MAX];
> 
> +    ArpTable arp_table;
> +
>      void *opaque;
>  };
> 
> --
> 1.7.4.1
> 

Looks good otherwise.

Jan

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