diff mbox series

[v7,1/2] resolv: implement ipv4+ipv6 flags in resolv.conf (bug 30544)

Message ID 20260429170104.2378474-1-pemensik@redhat.com (mailing list archive)
State New
Headers
Series [v7,1/2] resolv: implement ipv4+ipv6 flags in resolv.conf (bug 30544) |

Checks

Context Check Description
redhat-pt-bot/TryBot-apply_patch success Patch applied to master at the time it was sent

Commit Message

Petr Menšík April 29, 2026, 5 p.m. UTC 
  Add separate flags to mark support of address family. Its intention is
to react dynamically to changing network conditions. If the host has
IPv4 connectivity only, it would set ipv4 option. If it has also IPv6
connectivity, it would set ipv6 option. If it connects IPv6-only
network, then it set ipv6 only.

For backward compatibility it will keep old behaviour when both ipv4 and
ipv6 flags are missing. In this case it behaves the same way as if both
were present.

This is quite useful when default AF_UNSPEC is used in hints, but the
host is on network with just single AF used.

Unlike no-aaaa option it would change just AF_UNSPEC behaviour, ie.
getent ahosts example.com. getent ahostsv4 and getent ahostsv6 would
remain unmodified.

Signed-off-by: Petr Menšík <pemensik@redhat.com>
---
 resolv/nss_dns/dns-host.c             | 50 +++++++++++++++++----------
 resolv/res_debug.c                    |  2 ++
 resolv/res_init.c                     |  2 ++
 resolv/resolv.h                       |  2 ++
 resolv/tst-resolv-res_init-skeleton.c |  2 ++
 5 files changed, 40 insertions(+), 18 deletions(-)
diff mbox series

Patch

diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
index 728dae615d..16e45ce48d 100644
--- a/resolv/nss_dns/dns-host.c
+++ b/resolv/nss_dns/dns-host.c
@@ -379,6 +379,7 @@  _nss_dns_gethostbyname4_r (const char *name, struct gaih_addrtuple **pat,
 {
   enum nss_status status = check_name (name, herrnop);
   char tmp[NS_MAXDNAME];
+
   if (status != NSS_STATUS_SUCCESS)
     return status;
   struct resolv_context *ctx = __resolv_context_get ();
@@ -412,26 +413,39 @@  _nss_dns_gethostbyname4_r (const char *name, struct gaih_addrtuple **pat,
 
   int olderr = errno;
   int n;
+  unsigned long res_options = ctx->resp->options & (RES_NOAAAA|RES_IPV4|RES_IPV6);
+  int qtype;
 
-  if ((ctx->resp->options & RES_NOAAAA) == 0)
+  switch (res_options)
     {
-      n = __res_context_search (ctx, name, C_IN, T_QUERY_A_AND_AAAA,
-				dns_packet_buffer, sizeof (dns_packet_buffer),
-				&alt_dns_packet_buffer, &ans2p, &nans2p,
-				&resplen2, &ans2p_malloced);
-      if (n >= 0)
-	status = gaih_getanswer (alt_dns_packet_buffer, n, ans2p, resplen2,
-				 &abuf, pat, errnop, herrnop, ttlp);
-    }
-  else
-    {
-      n = __res_context_search (ctx, name, C_IN, T_A,
-				dns_packet_buffer, sizeof (dns_packet_buffer),
-				&alt_dns_packet_buffer, NULL, NULL, NULL, NULL);
-      if (n >= 0)
-	status = gaih_getanswer_noaaaa (alt_dns_packet_buffer, n,
-					&abuf, pat, errnop, herrnop, ttlp);
-    }
+      case RES_IPV4:
+      case RES_IPV4|RES_NOAAAA:
+      case RES_NOAAAA:
+      case RES_IPV6|RES_NOAAAA: /*< this combination should never be used.  */
+      case RES_IPV4|RES_IPV6|RES_NOAAAA: /*< this does not make sense.  */
+      case RES_IPV6: /*< oh we want AAAA, but not A here. code is the same.  */
+	qtype = (res_options == RES_IPV6 ? T_AAAA : T_A);
+	n = __res_context_search (ctx, name, C_IN, qtype,
+				  dns_packet_buffer, sizeof (dns_packet_buffer),
+				  &alt_dns_packet_buffer, NULL, NULL, NULL, NULL);
+	if (n >= 0)
+	  status = gaih_getanswer_noaaaa (alt_dns_packet_buffer, n,
+					  &abuf, pat, errnop, herrnop, ttlp);
+	break;
+
+      case 0:
+      case RES_IPV4|RES_IPV6:
+      default:
+	n = __res_context_search (ctx, name, C_IN, T_QUERY_A_AND_AAAA,
+				  dns_packet_buffer, sizeof (dns_packet_buffer),
+				  &alt_dns_packet_buffer, &ans2p, &nans2p,
+				  &resplen2, &ans2p_malloced);
+	if (n >= 0)
+	  status = gaih_getanswer (alt_dns_packet_buffer, n, ans2p, resplen2,
+				  &abuf, pat, errnop, herrnop, ttlp);
+	break;
+  }
+
   if (n < 0)
     {
       switch (errno)
diff --git a/resolv/res_debug.c b/resolv/res_debug.c
index 73af0c72fe..f73bccd7bd 100644
--- a/resolv/res_debug.c
+++ b/resolv/res_debug.c
@@ -613,6 +613,8 @@  p_option(u_long option) {
 	case RES_NORELOAD:	return "no-reload";
 	case RES_TRUSTAD:	return "trust-ad";
 	case RES_NOAAAA:	return "no-aaaa";
+	case RES_IPV4:		return "ipv4";
+	case RES_IPV6:		return "ipv6";
 				/* XXX nonreentrant */
 	default:		sprintf(nbuf, "?0x%lx?", (u_long)option);
 				return (nbuf);
diff --git a/resolv/res_init.c b/resolv/res_init.c
index 683ae9e9b2..d5f0311372 100644
--- a/resolv/res_init.c
+++ b/resolv/res_init.c
@@ -696,6 +696,8 @@  res_setoptions (struct resolv_conf_parser *parser, const char *options)
             { STRnLEN ("trust-ad"), RES_TRUSTAD },
             { STRnLEN ("no-aaaa"), RES_NOAAAA },
             { STRnLEN ("strict-error"), RES_STRICTERR },
+            { STRnLEN ("ipv4"), RES_IPV4 },
+            { STRnLEN ("ipv6"), RES_IPV6 },
           };
 #define noptions (sizeof (options) / sizeof (options[0]))
           bool negate_option = *cp == '-';
diff --git a/resolv/resolv.h b/resolv/resolv.h
index b8a0f66a5f..2459083fee 100644
--- a/resolv/resolv.h
+++ b/resolv/resolv.h
@@ -134,6 +134,8 @@  struct res_sym {
 #define RES_TRUSTAD     0x04000000 /* Request AD bit, keep it in responses.  */
 #define RES_NOAAAA      0x08000000 /* Suppress AAAA queries.  */
 #define RES_STRICTERR   0x10000000 /* Report more DNS errors as errors.  */
+#define RES_IPV4        0x20000000 /* Query A records on PF_UNSPEC hints.  */
+#define RES_IPV6        0x40000000 /* Query AAAA records on PF_UNSPEC hints.  */
 
 #define RES_DEFAULT	(RES_RECURSE|RES_DEFNAMES|RES_DNSRCH)
 
diff --git a/resolv/tst-resolv-res_init-skeleton.c b/resolv/tst-resolv-res_init-skeleton.c
index 1e4c59dac9..aec63656a9 100644
--- a/resolv/tst-resolv-res_init-skeleton.c
+++ b/resolv/tst-resolv-res_init-skeleton.c
@@ -130,6 +130,8 @@  print_resp (FILE *fp, res_state resp)
         print_option_flag (fp, &options, RES_TRUSTAD, "trust-ad");
         print_option_flag (fp, &options, RES_NOAAAA, "no-aaaa");
         print_option_flag (fp, &options, RES_STRICTERR, "strict-error");
+        print_option_flag (fp, &options, RES_IPV4, "ipv4");
+        print_option_flag (fp, &options, RES_IPV6, "ipv6");
         fputc ('\n', fp);
         if (options != 0)
           fprintf (fp, "; error: unresolved option bits: 0x%x\n", options);