resolver.3: Document missing options used by _res structure indicate defaults

Missing options: RES_INSECURE1, RES_INSECURE2, RES_NOALIASES,
USE_INET6, ROTATE, NOCHECKNAME, RES_KEEPTSIG, BLAST, USEBSTRING,
NOIP6DOTINT, USE_EDNS0, SNGLKUP, SNGLKUPREOP, RES_USE_DNSSEC,
NOTLDQUERY, DEFAULT

Written from the glibc source and resolv.conf.5.

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=527136

Reported-by: Jakub Wilk <ubanus@users.sf.net>
Signed-off-by: Stéphane Aulery <saulery@free.fr>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/resolver.3

@@ -197,19 +197,20 @@ which is not the default.
 Accept authoritative answers only.
 .BR res_send ()
 continues until
-it finds an authoritative answer or returns an error.  [Not currently
-implemented].
+it finds an authoritative answer or returns an error.
+[Not currently implemented].
 .TP
 .B RES_USEVC
 Use TCP connections for queries rather than UDP datagrams.
 .TP
 .B RES_PRIMARY
 Query primary domain name server only.
+[Not currently implemented].
 .TP
 .B RES_IGNTC
 Ignore truncation errors.
-Don't retry with TCP.  [Not currently
-implemented].
+Don't retry with TCP.
+[Not currently implemented].
 .TP
 .B RES_RECURSE
 Set the recursion desired bit in queries.
@@ -238,10 +239,92 @@ domain and in parent domains.
 This option is used by
 .BR gethostbyname (3).
 [Enabled by default].
-.PP
-This list is not complete.
-You can find some other flags described in
-.BR resolv.conf (5).
+.TP
+.B RES_INSECURE1
+Accept a response from a wrong server and show it on standard output
+(for debug purpose only).
+.TP
+.B RES_INSECURE2
+Accept a response which contains a wrong query and show it on standard
+output (for debug purpose only).
+.TP
+.B RES_NOALIASES
+Disable usage of
+.B HOSTALIASES
+environment variable.
+.TP
+.B RES_USE_INET6
+Try an AAAA query before an A query inside the
+.BR gethostbyname ()
+function, and map IPv4 responses in IPv6 "tunneled form" if no AAAA records
+are found but an A record set exists.
+.TP
+.B RES_ROTATE
+Causes round-robin selection of name servers from among those listed.
+This has the effect of spreading the query load among all listed servers,
+rather than having all clients try the first listed server first every
+time.
+.TP
+.B RES_NOCHECKNAME
+Disable the modern BIND checking of incoming hostnames and mail names
+for invalid characters such as underscore (_), non-ASCII,
+or control characters.
+[Not currently implemented].
+.TP
+.B RES_KEEPTSIG
+Do not strip TSIG records.
+[Not currently implemented].
+.TP
+.B RES_BLAST
+Send each query simultaneously and recursively to all servers.
+Note this option overrides
+.BR RES_ROTATE .
+.TP
+.BR RES_USEBSTRING " (since glibc 2.3.4)"
+Make reverse IPv6 lookups using the bit-label format described in RFC 2673;
+if this option is not set, then nibble format is used.
+.TP
+.B RES_NOIP6DOTINT
+Use
+.I ip6.arpa
+zone in IPv6 reverse lookup instead of
+.IR ip6.int ,
+which is deprecated since glibc 2.3.4.
+[Enabled by default].
+.TP
+.BR RES_USE_EDNS0 " (since glibc 2.6)"
+Enables support for the DNS extensions (EDNS0) described in RFC 2671.
+.TP
+.BR RES_SNGLKUP " (since glibc 2.10)"
+By default, glibc performs IPv4 and IPv6 lookups in parallel since
+version 2.9.
+Some appliance DNS servers cannot handle these queries properly
+and make the requests time out.
+This option disables the behavior and makes glibc
+perform the IPv6 and IPv4 requests sequentially
+(at the cost of some slowdown of the resolving process).
+.TP
+.B RES_SNGLKUPREOP
+When
+.B RES_SNGLKUP
+option is enabled, opens a new socket for the each request.
+.TP
+.B RES_USE_DNSSEC
+Use DNSSEC with OK bit in OPT record.
+This option implies
+.BR RES_USE_EDNS0 .
+.TP
+.B RES_NOTLDQUERY
+Do not look up unqualified name as a top-level domain (TLD).
+.TP
+.B RES_DEFAULT
+Default option which implies:
+.BR RES_RECURSE ,
+.BR RES_DEFNAMES ,
+.BR RES_DNSRCH
+and
+.BR RES_NOIP6DOTINT .
+
 .SH RETURN VALUE
 The
 .BR res_init ()