resolv: Introduce struct resolv_context [BZ #21668]

struct resolv_context objects provide a temporary resolver context
which does not change during a name lookup operation.  Only when the
outmost context is created, the stub resolver configuration is
verified to be current (at present, only against previous res_init
calls).  Subsequent attempts to obtain the context will reuse the
result of the initial verification operation.

struct resolv_context can also be extended in the future to store
data which needs to be deallocated during thread cancellation.

1 files changed, 49 insertions, 0 deletions

diff --git a/resolv/res_use_inet6.h b/resolv/res_use_inet6.h
new file mode 100644
index 0000000000..8649833072
--- /dev/null
+++ b/resolv/res_use_inet6.h
@@ -0,0 +1,49 @@
+/* Support functions for handling RES_USE_INET6 in getaddrinfo/nscd.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _RES_USE_INET6_H
+#define _RES_USE_INET6_H
+
+#include <resolv/resolv_context.h>
+#include <resolv/resolv-internal.h>
+
+/* Ensure that RES_USE_INET6 is disabled in *CTX.  Return true if
+   __resolv_context_enable_inet6 below should enable RES_USE_INET6
+   again.  */
+static inline bool
+__resolv_context_disable_inet6 (struct resolv_context *ctx)
+{
+  if (ctx != NULL && ctx->resp->options & DEPRECATED_RES_USE_INET6)
+    {
+      ctx->resp->options &= ~DEPRECATED_RES_USE_INET6;
+      return true;
+    }
+  else
+    return false;
+}
+
+/* If ENABLE, re-enable RES_USE_INET6 in *CTX.  To be paired with
+   __resolv_context_disable_inet6.  */
+static inline void
+__resolv_context_enable_inet6 (struct resolv_context *ctx, bool enable)
+{
+  if (ctx != NULL && enable)
+    ctx->resp->options |= DEPRECATED_RES_USE_INET6;
+}
+
+#endif