Provide GLIBC_PRIVATE symbols no longer used by the current library

version to increase backwards compatibility during glibc updates.

This will help to avoid some of the issues that surface while a

glibc update is performed with concurrent application updates,

and it also allows old nscd to trigger cache invalidation in a

running nscd daemon.

While at this, also add interfaces for supporting old nss_dns modules.

This patch is not needed upstream because upstream does not provide

backwards compatibility for GLIBC_PRIVATE symbols.

diff --git a/inet/herrno.c b/inet/herrno.c

index 0cd84445190728b3..4d26e9b254181422 100644

--- a/inet/herrno.c

+++ b/inet/herrno.c

@@ -28,3 +28,9 @@ __thread int __h_errno;

 extern __thread int __libc_h_errno __attribute__ ((alias ("__h_errno")))

   attribute_hidden;

 #define h_errno __libc_h_errno

+

+#ifdef SHARED

+/* Provide an alias for use by the old libpthread.so.0 during

+   updates.  */

+asm (".symver __h_errno, h_errno@GLIBC_PRIVATE");

+#endif

diff --git a/resolv/res_libc.c b/resolv/res_libc.c

index 9f2d3c3bd442bb38..5ab02c79c72eb1ac 100644

--- a/resolv/res_libc.c

+++ b/resolv/res_libc.c

@@ -41,6 +41,7 @@

 #include <resolv.h>

 #include <libc-lock.h>

 #include <resolv-internal.h>

+#include <resolv_context.h>

 int

 res_init (void)

@@ -80,7 +81,34 @@ res_init (void)

   return __res_vinit (&_res, 1);

 }

-

+

+#ifdef SHARED

+

+/* An old nscd binary may bind to __res_maybe_init during a glibc

+   update.  Emulate it using the new functions.  Ignore PREINIT

+   because almost all existing __res_maybe_init callers used zero

+   PREINIT, and the difference for RESP == &_res is very minor (a

+   potential override of application configuration).  */

+attribute_compat_text_section

+int

+__res_maybe_init (res_state resp, int preinit)

+{

+  if (resp == &_res)

+    {

+      /* This performs an implicit initialization of _res.  */

+      struct resolv_context *ctx = __resolv_context_get ();

+      if (ctx == NULL)

+        return -1;

+      __resolv_context_put (ctx);

+      return 0;

+    }

+  else

+    return __res_vinit (resp, 0);

+}

+asm (".symver __res_maybe_init, __res_maybe_init@GLIBC_PRIVATE");

+

+#endif /* SHARED */

+

 /* This needs to be after the use of _res in res_init, above.  */

 #undef _res

diff --git a/resolv/res_query.c b/resolv/res_query.c

index ebbe5a6a4ed86abe..24fefb561e7f1f5e 100644

--- a/resolv/res_query.c

+++ b/resolv/res_query.c

@@ -705,6 +705,96 @@ hostalias (const char *name)

     (__resolv_context_get (), name, abuf, sizeof (abuf));

 }

+#ifdef SHARED

+/* Compatibiliaty functions to support old nss_dns modules.  */

+

+typedef int (*compat_query_function) (struct resolv_context *,

+				      const char *name,

+				      int class, int type,

+				      u_char *answer,

+				      int anslen,

+				      u_char **answerp,

+				      u_char **answerp2,

+				      int *nanswerp2,

+				      int *resplen2,

+				      int *answerp2_malloced);

+

+attribute_compat_text_section

+static int

+wrap_compat_call (compat_query_function qf,

+		  res_state statp,

+		  const char *name,	/* domain name */

+		  int class, int type,	/* class and type of query */

+		  u_char *answer,	/* buffer to put answer */

+		  int anslen,		/* size of answer buffer */

+		  u_char **answerp,	/* if buffer needs to be enlarged */

+		  u_char **answerp2,

+		  int *nanswerp2,

+		  int *resplen2,

+		  int *answerp2_malloced)

+{

+  if (statp == &_res)

+    {

+      struct resolv_context *ctx = __resolv_context_get ();

+      if (ctx == NULL)

+	{

+	  __set_h_errno (NO_RECOVERY);

+	  return -1;

+	}

+      int ret = qf (ctx, name, class, type,

+		    answer, anslen, answerp, answerp2,

+		    nanswerp2, resplen2, answerp2_malloced);

+      __resolv_context_put (ctx);

+      return ret;

+    }

+  else

+    {

+      __set_h_errno (NO_RECOVERY);

+      __set_errno (ENOTSUP);

+      return -1;

+    }

+}

+

+attribute_compat_text_section

+int

+__libc_res_nquery(res_state statp,

+		  const char *name,	/* domain name */

+		  int class, int type,	/* class and type of query */

+		  u_char *answer,	/* buffer to put answer */

+		  int anslen,		/* size of answer buffer */

+		  u_char **answerp,	/* if buffer needs to be enlarged */

+		  u_char **answerp2,

+		  int *nanswerp2,

+		  int *resplen2,

+		  int *answerp2_malloced)

+{

+  return wrap_compat_call (__res_context_query, statp, name, class, type,

+			   answer, anslen, answerp, answerp2,

+			   nanswerp2, resplen2, answerp2_malloced);

+}

+asm (".symver __libc_res_nquery, __libc_res_nquery@GLIBC_PRIVATE");

+

+attribute_compat_text_section

+int

+__libc_res_nsearch(res_state statp,

+		   const char *name,	/* domain name */

+		   int class, int type,	/* class and type of query */

+		   u_char *answer,	/* buffer to put answer */

+		   int anslen,		/* size of answer */

+		   u_char **answerp,

+		   u_char **answerp2,

+		   int *nanswerp2,

+		   int *resplen2,

+		   int *answerp2_malloced)

+{

+  return wrap_compat_call (__res_context_search, statp, name, class, type,

+			   answer, anslen, answerp, answerp2,

+			   nanswerp2, resplen2, answerp2_malloced);

+}

+asm (".symver __libc_res_nsearch, __libc_res_nsearch@GLIBC_PRIVATE");

+

+#endif /* SHARED */

+

 #if SHLIB_COMPAT (libresolv, GLIBC_2_0, GLIBC_2_2)

 # undef res_query

 # undef res_querydomain