Fix --mtu-disc maybe|yes on Linux.

--mtu-disc (on Linux) needs two components to work:
   - setsockopt() with IP_MTU_DISCOVER or IPV6_MTU_DISCOVER
   - "extended error reporting" (setsockopt(IP_RECVERR) and
     then via mtu.c/format_extended_socket_error()) to react on
     "packet too big" errors on sendto() / sendmsg()

Some configure.ac reorganization broke detection of <linux/errqueue.h>
and "struct sock_extended_err".  Re-add <linux/errqueue.h> to configure.ac,
remove all the other conditionals in syshead.h, and remove the
"struct sock_extended_err" check completely (assumption: if errqueue.h
exists, it contains what we need).

Thus, the "non-helpful" socket error message turns into:

2022-02-22 12:31:42 write UDPv4 [EMSGSIZE Path-MTU=800]: Message too long (fd=3,code=90)
2022-02-22 12:31:42 Note adjusting 'mssfix 1400 mtu' to 'mssfix 800 mtu' according to path MTU discovery
2022-02-22 12:31:42 Note adjusting 'fragment 1400 mtu' to 'fragment 800 mtu' according to path MTU discovery

... while at it, fix extra space in first part of these messages, and
print o->ce.fragment for the "fragment" message...

v2: assume that "if it's linux, and has these two headers, everything
else will be there as well" and get rid of most of the #ifdef checks

Trac: #1452

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20220222113832.13383-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg23863.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/openvpn/mss.c b/src/openvpn/mss.c
index 81692e9..25b2640 100644
--- a/src/openvpn/mss.c
+++ b/src/openvpn/mss.c
@@ -361,7 +361,7 @@ frame_adjust_path_mtu(struct context *c)
         || (o->ce.mssfix_encap && pmtu < o->ce.mssfix + encap_overhead))
     {
         const char* mtustr = o->ce.mssfix_encap ? " mtu" : "";
-        msg(D_MTU_INFO, "Note adjusting 'mssfix %d %s' to 'mssfix %d mtu' "
+        msg(D_MTU_INFO, "Note adjusting 'mssfix %d%s' to 'mssfix %d mtu' "
                         "according to path MTU discovery", o->ce.mssfix,
             mtustr, pmtu);
         o->ce.mssfix = pmtu;
@@ -374,8 +374,8 @@ frame_adjust_path_mtu(struct context *c)
         (o->ce.fragment_encap && pmtu < o->ce.fragment + encap_overhead))
     {
         const char* mtustr = o->ce.fragment_encap ? " mtu" : "";
-        msg(D_MTU_INFO, "Note adjusting 'fragment %d %s' to 'fragment %d mtu' "
-                        "according to path MTU discovery", o->ce.mssfix,
+        msg(D_MTU_INFO, "Note adjusting 'fragment %d%s' to 'fragment %d mtu' "
+                        "according to path MTU discovery", o->ce.fragment,
             mtustr, pmtu);
         o->ce.fragment = pmtu;
         o->ce.fragment_encap = true;