[Patch] [BZ 14505] Avoid unwanted A lookups on IPV6 only host

[Jeff Law]

On 08/21/2012 04:06 PM, Roland McGrath wrote:
> Seems simpler to test "&& req->ai_family == PF_UNSPEC".
> Also, you shouldn't call __nss_lookup_function at all when
> you're not going to use its result.  So make it:
>
> 	      nss_gethostbyname4_r fct4 = NULL;
> 	      /* comment */
> 	      if (req->ai_family == PF_UNSPEC)
> 	        fct4 = __nss_lookup_function (nip, "gethostbyname4_r");
> 	      if (fct4 != NULL)
Thanks.  I went back and forth between testing PF_UNSPEC and testing for 
PF_INET/PF_INET6 and selected the latter because I thought it was 
marginally clearer.  It's certainly not a big deal to me.  Testing 
PF_UNSPEC is slight more efficient from a code generation standpoint.

Totally agreed on avoiding the nss_lookup_function call.

Updated patch & ChangeLog entry attached.



-------------- next part --------------
2012-08-22  Jeff Law <law@redhat.com>

	
	[BZ #14505]
	* sysdeps/posix/getaddrinfo.c (gaih_inet): Only use gethostbyname4_r
	if the family is PF_UNSPEC.


 
diff --git a/sysdeps/posix/getaddrinfo.c b/sysdeps/posix/getaddrinfo.c
index 81e928a..05883bd 100644
--- a/sysdeps/posix/getaddrinfo.c
+++ b/sysdeps/posix/getaddrinfo.c
@@ -832,8 +832,13 @@ gaih_inet (const char *name, const struct gaih_service *service,
 	  while (!no_more)
 	    {
 	      no_data = 0;
-	      nss_gethostbyname4_r fct4
-		= __nss_lookup_function (nip, "gethostbyname4_r");
+	      nss_gethostbyname4_r fct4 = NULL;
+
+	      /* gethostbyname4_r sends out parallel A and AAAA queries and
+		 is thus only suitable for PF_UNSPEC.  */
+	      if (req->ai_family == PF_UNSPEC)
+		fct4 = __nss_lookup_function (nip, "gethostbyname4_r");
+
 	      if (fct4 != NULL)
 		{
 		  int herrno;