linux-user: manage bind with a socket of SOCK_PACKET type.

This is obsolete, but if we want to use dhcp with an old distro (like debian
etch), we need it. Some users (like dhclient) use SOCK_PACKET with AF_PACKET
and the kernel allows that.

packet(7)

  In Linux 2.0, the only way to  get  a  packet  socket  was  by calling
  socket(AF_INET,  SOCK_PACKET,  protocol).   This is still supported but
  strongly deprecated.  The main difference between the  two methods  is
  that  SOCK_PACKET uses the old struct sockaddr_pkt to specify an inter‐
  face, which doesn't provide physical layer independence.

     struct sockaddr_pkt {
         unsigned short spkt_family;
         unsigned char  spkt_device[14];
         unsigned short spkt_protocol;
     };

  spkt_family contains the device type, spkt_protocol is the  IEEE 802.3
  protocol  type  as  defined  in <sys/if_ether.h> and spkt_device is the
  device name as a null-terminated string, for example, eth0.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/syscall.c

@@ -2090,6 +2090,30 @@ static int sock_flags_fixup(int fd, int target_type)
     return fd;
 }
 
+static abi_long packet_target_to_host_sockaddr(void *host_addr,
+                                               abi_ulong target_addr,
+                                               socklen_t len)
+{
+    struct sockaddr *addr = host_addr;
+    struct target_sockaddr *target_saddr;
+
+    target_saddr = lock_user(VERIFY_READ, target_addr, len, 1);
+    if (!target_saddr) {
+        return -TARGET_EFAULT;
+    }
+
+    memcpy(addr, target_saddr, len);
+    addr->sa_family = tswap16(target_saddr->sa_family);
+    /* spkt_protocol is big-endian */
+
+    unlock_user(target_saddr, target_addr, 0);
+    return 0;
+}
+
+static TargetFdTrans target_packet_trans = {
+    .target_to_host_addr = packet_target_to_host_sockaddr,
+};
+
 /* do_socket() Must return target values and target errnos. */
 static abi_long do_socket(int domain, int type, int protocol)
 {
@@ -2112,6 +2136,12 @@ static abi_long do_socket(int domain, int type, int protocol)
     ret = get_errno(socket(domain, type, protocol));
     if (ret >= 0) {
         ret = sock_flags_fixup(ret, target_type);
+        if (type == SOCK_PACKET) {
+            /* Manage an obsolete case :
+             * if socket type is SOCK_PACKET, bind by name
+             */
+            fd_trans_register(ret, &target_packet_trans);
+        }
     }
     return ret;
 }