nss_dns: Remove RES_USE_INET6 handling

  Since commit 3f8b44be0a658266adff5ece1e4bc3ce097a5dbe ("resolv:
Remove support for RES_USE_INET6 and the inet6 option"),
res_use_inet6 () always evaluates to false.

2019-05-16  Florian Weimer  <fweimer@redhat.com>

	* resolv/nss_dns/dns-host.c (gethostbyname3_context): Do not
	perform IPv6 lookup.
	(_nss_dns_gethostbyname_r): Do not request IPv4 address mapping
	from gethostbyname3_context.
  

* Florian Weimer:

> Since commit 3f8b44be0a658266adff5ece1e4bc3ce097a5dbe ("resolv:
> Remove support for RES_USE_INET6 and the inet6 option"),
> res_use_inet6 () always evaluates to false.
>
> 2019-05-16  Florian Weimer  <fweimer@redhat.com>
>
> 	* resolv/nss_dns/dns-host.c (gethostbyname3_context): Do not
> 	perform IPv6 lookup.
> 	(_nss_dns_gethostbyname_r): Do not request IPv4 address mapping
> 	from gethostbyname3_context.

I forgot to update the ChangeLog entry after making further cleanups:

2019-05-17  Florian Weimer  <fweimer@redhat.com>

	* resolv/nss_dns/dns-host.c (gethostbyname3_context): Do not
	perform IPv6 lookup.  Adjust getanswer_r call.
	(_nss_dns_gethostbyname_r): Do not request IPv4 address mapping
	from gethostbyname3_context.
	(_nss_dns_gethostbyaddr2_r): Adjust getanswer_r call.
	(getanswer_r): Remove map argument.  Do not perform address
	mapping.

Florian

> diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
> index 9c40051aff..40c23dfe00 100644
> --- a/resolv/nss_dns/dns-host.c
> +++ b/resolv/nss_dns/dns-host.c
> @@ -85,10 +85,6 @@
>  #include <resolv/resolv-internal.h>
>  #include <resolv/resolv_context.h>
>  
> -/* Get implementations of some internal functions.  */
> -#include <resolv/mapv4v6addr.h>
> -#include <resolv/mapv4v6hostent.h>
> -
>  #define RESOLVSORT
>  
>  #if PACKETSZ > 65536
> @@ -114,7 +110,7 @@ static enum nss_status getanswer_r (struct resolv_context *ctx,
>  				    const char *qname, int qtype,
>  				    struct hostent *result, char *buffer,
>  				    size_t buflen, int *errnop, int *h_errnop,
> -				    int map, int32_t *ttlp, char **canonp);
> +				    int32_t *ttlp, char **canonp);
>  
>  static enum nss_status gaih_getanswer (const querybuf *answer1, int anslen1,
>  				       const querybuf *answer2, int anslen2,
> @@ -182,7 +178,6 @@ gethostbyname3_context (struct resolv_context *ctx,
>    char tmp[NS_MAXDNAME];
>    int size, type, n;
>    const char *cp;
> -  int map = 0;
>    int olderr = errno;
>    enum nss_status status;
>  
> @@ -244,31 +239,14 @@ gethostbyname3_context (struct resolv_context *ctx,
>        else
>  	__set_errno (olderr);
>  
> -      /* If we are looking for an IPv6 address and mapping is enabled
> -	 by having the RES_USE_INET6 bit in _res.options set, we try
> -	 another lookup.  */
> -      if (af == AF_INET6 && res_use_inet6 ())
> -	n = __res_context_search (ctx, name, C_IN, T_A, host_buffer.buf->buf,
> -				  host_buffer.buf != orig_host_buffer
> -				  ? MAXPACKET : 1024, &host_buffer.ptr,
> -				  NULL, NULL, NULL, NULL);
> -
> -      if (n < 0)
> -	{
> -	  if (host_buffer.buf != orig_host_buffer)
> -	    free (host_buffer.buf);
> -	  return status;
> -	}
> -
> -      map = 1;
> -
> -      result->h_addrtype = AF_INET;
> -      result->h_length = INADDRSZ;
> +      if (host_buffer.buf != orig_host_buffer)
> +	free (host_buffer.buf);
> +      return status;
>      }
>  
>    status = getanswer_r
>      (ctx, host_buffer.buf, n, name, type, result, buffer, buflen,
> -     errnop, h_errnop, map, ttlp, canonp);
> +     errnop, h_errnop, ttlp, canonp);
>    if (host_buffer.buf != orig_host_buffer)
>      free (host_buffer.buf);
>    return status;
> @@ -314,13 +292,8 @@ _nss_dns_gethostbyname_r (const char *name, struct hostent *result,
>        *h_errnop = NETDB_INTERNAL;
>        return NSS_STATUS_UNAVAIL;
>      }
> -  status = NSS_STATUS_NOTFOUND;
> -  if (res_use_inet6 ())
> -    status = gethostbyname3_context (ctx, name, AF_INET6, result, buffer,
> -				     buflen, errnop, h_errnop, NULL, NULL);
> -  if (status == NSS_STATUS_NOTFOUND)
> -    status = gethostbyname3_context (ctx, name, AF_INET, result, buffer,
> -				     buflen, errnop, h_errnop, NULL, NULL);
> +  status = gethostbyname3_context (ctx, name, AF_INET, result, buffer,
> +				   buflen, errnop, h_errnop, NULL, NULL);
>    __resolv_context_put (ctx);
>    return status;
>  }
> @@ -547,7 +520,7 @@ _nss_dns_gethostbyaddr2_r (const void *addr, socklen_t len, int af,
>  
>    status = getanswer_r
>      (ctx, host_buffer.buf, n, qbuf, T_PTR, result, buffer, buflen,
> -     errnop, h_errnop, 0 /* XXX */, ttlp, NULL);
> +     errnop, h_errnop, ttlp, NULL);
>    if (host_buffer.buf != orig_host_buffer)
>      free (host_buffer.buf);
>    if (status != NSS_STATUS_SUCCESS)
> @@ -627,7 +600,7 @@ static enum nss_status
>  getanswer_r (struct resolv_context *ctx,
>  	     const querybuf *answer, int anslen, const char *qname, int qtype,
>  	     struct hostent *result, char *buffer, size_t buflen,
> -	     int *errnop, int *h_errnop, int map, int32_t *ttlp, char **canonp)
> +	     int *errnop, int *h_errnop, int32_t *ttlp, char **canonp)
>  {
>    struct host_data
>    {
> @@ -645,7 +618,6 @@ getanswer_r (struct resolv_context *ctx,
>    const char *tname;
>    int (*name_ok) (const char *);
>    u_char packtmp[NS_MAXCDNAME];
> -  int have_to_map = 0;
>    uintptr_t pad = -(uintptr_t) buffer % __alignof__ (struct host_data);
>    buffer += pad;
>    buflen = buflen > pad ? buflen - pad : 0;
> @@ -870,9 +842,7 @@ getanswer_r (struct resolv_context *ctx,
>  	  continue;
>  	}
>  
> -      if (type == T_A && qtype == T_AAAA && map)
> -	have_to_map = 1;
> -      else if (__glibc_unlikely (type != qtype))
> +      if (__glibc_unlikely (type != qtype))
>  	{
>  	  cp += n;
>  	  continue;			/* XXX - had_error++ ? */
> @@ -995,9 +965,6 @@ getanswer_r (struct resolv_context *ctx,
>  	  linebuflen -= n;
>  	}
>  
> -      if (have_to_map)
> -	if (map_v4v6_hostent (result, &bp, &linebuflen))
> -	  goto too_small;
>        *h_errnop = NETDB_SUCCESS;
>        return NSS_STATUS_SUCCESS;
>      }