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, 32 insertions, 10 deletions

diff --git a/nss/getnssent_r.c b/nss/getnssent_r.c
index 5fdbf3be00..d85065b6cc 100644
--- a/nss/getnssent_r.c
+++ b/nss/getnssent_r.c
@@ -18,6 +18,7 @@
 #include <errno.h>
 #include <netdb.h>
 #include "nsswitch.h"
+#include <resolv/resolv_context.h>
 
 /* Set up NIP to run through the services.  If ALL is zero, use NIP's
    current location if it's not nil.  Return nonzero if there are no
@@ -59,10 +60,15 @@ __nss_setent (const char *func_name, db_lookup_function lookup_fct,
   } fct;
   int no_more;
 
-  if (res && __res_maybe_init (&_res, 0) == -1)
+  struct resolv_context *res_ctx = NULL;
+  if (res)
     {
-      __set_h_errno (NETDB_INTERNAL);
-      return;
+      res_ctx = __resolv_context_get ();
+      if (res_ctx == NULL)
+	{
+	  __set_h_errno (NETDB_INTERNAL);
+	  return;
+	}
     }
 
   /* Cycle through the services and run their `setXXent' functions until
@@ -95,6 +101,8 @@ __nss_setent (const char *func_name, db_lookup_function lookup_fct,
 	*last_nip = *nip;
     }
 
+  __resolv_context_put (res_ctx);
+
   if (stayopen_tmp)
     *stayopen_tmp = stayopen;
 }
@@ -112,10 +120,15 @@ __nss_endent (const char *func_name, db_lookup_function lookup_fct,
   } fct;
   int no_more;
 
-  if (res && __res_maybe_init (&_res, 0) == -1)
+  struct resolv_context *res_ctx = NULL;
+  if (res)
     {
-      __set_h_errno (NETDB_INTERNAL);
-      return;
+      res_ctx = __resolv_context_get ();
+      if (res_ctx == NULL)
+	{
+	  __set_h_errno (NETDB_INTERNAL);
+	  return;
+	}
     }
 
   /* Cycle through all the services and run their endXXent functions.  */
@@ -132,6 +145,8 @@ __nss_endent (const char *func_name, db_lookup_function lookup_fct,
       no_more = __nss_next2 (nip, func_name, NULL, &fct.ptr, 0, 1);
     }
   *last_nip = *nip = NULL;
+
+  __resolv_context_put (res_ctx);
 }
 
 
@@ -152,11 +167,16 @@ __nss_getent_r (const char *getent_func_name,
   int no_more;
   enum nss_status status;
 
-  if (res && __res_maybe_init (&_res, 0) == -1)
+  struct resolv_context *res_ctx = NULL;
+  if (res)
     {
-      *h_errnop = NETDB_INTERNAL;
-      *result = NULL;
-      return errno;
+      res_ctx = __resolv_context_get ();
+      if (res_ctx == NULL)
+	{
+	  *h_errnop = NETDB_INTERNAL;
+	  *result = NULL;
+	  return errno;
+	}
     }
 
   /* Initialize status to return if no more functions are found.  */
@@ -227,6 +247,8 @@ __nss_getent_r (const char *getent_func_name,
       while (! no_more && status != NSS_STATUS_SUCCESS);
     }
 
+  __resolv_context_put (res_ctx);
+
   *result = status == NSS_STATUS_SUCCESS ? resbuf : NULL;
   return (status == NSS_STATUS_SUCCESS ? 0
 	  : status != NSS_STATUS_TRYAGAIN ? ENOENT