syslogd: Handle connection errors when setting up forwarding sockets

[markj]

Summary

Suppose a forwarding host is identified by a hostname. We will attempt
to set up a connected forwarding socket for each address returned by
getaddrinfo(). However, a failure to connect some of these sockets
shouldn't be fatal.

PR: 293758

[ae]

No, it doesn't help.

17146 syslogd  CALL  socket(PF_INET6,0x10000002<SOCK_DGRAM|SOCK_CLOEXEC>,IPPROTO_UDP)
17146 syslogd  RET   socket 5
17146 syslogd  CALL  connect(0x5,0x23c6f2034820,0x1c)
17146 syslogd  STRU  struct sockaddr { AF_INET6, [2a02:XXX::XXX]:1 }
17146 syslogd  RET   connect -1 errno 65 No route to host
17146 syslogd  CALL  close(0x5)
17146 syslogd  RET   close 0
17146 syslogd  CALL  socket(PF_INET,0x10000002<SOCK_DGRAM|SOCK_CLOEXEC>,IPPROTO_UDP)
17146 syslogd  RET   socket 5
17146 syslogd  CALL  connect(0x5,0x23c6f2034820,0x10)
17146 syslogd  STRU  struct sockaddr { AF_INET, 141.XXX.XXX.XXX:1 }
17146 syslogd  RET   connect -1 errno 51 Network is unreachable
17146 syslogd  CALL  close(0x5)
17146 syslogd  RET   close 0
17146 syslogd  CALL  socket(PF_INET6,0x2<SOCK_DGRAM>,IPPROTO_IP)
17146 syslogd  RET   socket 5
17146 syslogd  CALL  setsockopt(0x5,SOL_SOCKET,SO_REUSEPORT,0x23c6f20349fc,0x4)
17146 syslogd  RET   setsockopt 0
17146 syslogd  CALL  bind(0x5,0x4b0c58c436d8,0x1c)
17146 syslogd  STRU  struct sockaddr { AF_INET6, [::]:514 }
17146 syslogd  RET   bind 0
17146 syslogd  CALL  connect(0x5,0x4b0c58c132b0,0x1c)
17146 syslogd  STRU  struct sockaddr { AF_INET6, [2a02:XXX::XXX]:514 }
17146 syslogd  RET   connect -1 errno 65 No route to host
17146 syslogd  CALL  close(0x5)
17146 syslogd  RET   close 0
17146 syslogd  CALL  socket(PF_INET6,0x2<SOCK_DGRAM>,IPPROTO_IP)
17146 syslogd  RET   socket 5
17146 syslogd  CALL  connect(0x5,0x4b0c58c132b0,0x1c)
17146 syslogd  STRU  struct sockaddr { AF_INET6, [2a02:XXX::XXX]:514 }
17146 syslogd  RET   connect -1 errno 65 No route to host
17146 syslogd  CALL  close(0x5)
17146 syslogd  RET   close 0
17146 syslogd  CALL  socket(PF_INET,0x2<SOCK_DGRAM>,IPPROTO_IP)
17146 syslogd  RET   socket 5
17146 syslogd  CALL  setsockopt(0x5,SOL_SOCKET,SO_REUSEPORT,0x23c6f20349fc,0x4)
17146 syslogd  RET   setsockopt 0
17146 syslogd  CALL  bind(0x5,0x4b0c58c4f0c8,0x10)
17146 syslogd  STRU  struct sockaddr { AF_INET, 0.0.0.0:514 }
17146 syslogd  RET   bind 0
17146 syslogd  CALL  connect(0x5,0x4b0c58c12230,0x10)
17146 syslogd  STRU  struct sockaddr { AF_INET, 141.XXX.XXX.XXX:514 }
17146 syslogd  RET   connect -1 errno 51 Network is unreachable
17146 syslogd  CALL  close(0x5)
17146 syslogd  RET   close 0
17146 syslogd  CALL  socket(PF_INET,0x2<SOCK_DGRAM>,IPPROTO_IP)
17146 syslogd  RET   socket 5
17146 syslogd  CALL  connect(0x5,0x4b0c58c12230,0x10)
17146 syslogd  STRU  struct sockaddr { AF_INET, 141.XXX.XXX.XXX:514 }
17146 syslogd  RET   connect -1 errno 51 Network is unreachable
17146 syslogd  CALL  close(0x5)
17146 syslogd  RET   close 0
17146 syslogd  CALL  write(0x2,0x23c6f2034250,0x9)
17146 syslogd  GIO   fd 2 wrote 9 bytes
      "syslogd: "
17146 syslogd  RET   write 9
17146 syslogd  CALL  write(0x2,0x23c6f2034340,0x3a)
17146 syslogd  GIO   fd 2 wrote 58 bytes
      "failed to create forwarding socket for HOSTNAME.DOMAIN"
17146 syslogd  RET   write 58/0x3a
17146 syslogd  CALL  write(0x2,0x23c6f7472107,0x1)
17146 syslogd  GIO   fd 2 wrote 1 byte
      "
      "
17146 syslogd  RET   write 1
17146 syslogd  CALL  _exit(0x1)

As I understand, due to capability mode we cannot use sendto and connect when syslogd is already started and configured.
Probably, specified address is not reachable during boot time and its route will appear when routing daemon will start.
But bird has # REQUIRE: DAEMON in its startup script and it will start much later.