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, 15 insertions, 6 deletions

diff --git a/resolv/nss_dns/dns-network.c b/resolv/nss_dns/dns-network.c
index dc1599b471..f190eb2225 100644
--- a/resolv/nss_dns/dns-network.c
+++ b/resolv/nss_dns/dns-network.c
@@ -67,6 +67,8 @@
 #include "nsswitch.h"
 #include <arpa/inet.h>
 #include <arpa/nameser.h>
+#include <resolv/resolv-internal.h>
+#include <resolv/resolv_context.h>
 
 /* Maximum number of aliases we allow.  */
 #define MAX_NR_ALIASES	48
@@ -115,7 +117,8 @@ _nss_dns_getnetbyname_r (const char *name, struct netent *result,
   int anslen;
   enum nss_status status;
 
-  if (__res_maybe_init (&_res, 0) == -1)
+  struct resolv_context *ctx = __resolv_context_get ();
+  if (ctx == NULL)
     {
       *errnop = errno;
       *herrnop = NETDB_INTERNAL;
@@ -124,14 +127,16 @@ _nss_dns_getnetbyname_r (const char *name, struct netent *result,
 
   net_buffer.buf = orig_net_buffer = (querybuf *) alloca (1024);
 
-  anslen = __libc_res_nsearch (&_res, name, C_IN, T_PTR, net_buffer.buf->buf,
-			       1024, &net_buffer.ptr, NULL, NULL, NULL, NULL);
+  anslen = __res_context_search
+    (ctx, name, C_IN, T_PTR, net_buffer.buf->buf,
+     1024, &net_buffer.ptr, NULL, NULL, NULL, NULL);
   if (anslen < 0)
     {
       /* Nothing found.  */
       *errnop = errno;
       if (net_buffer.buf != orig_net_buffer)
 	free (net_buffer.buf);
+      __resolv_context_put (ctx);
       return (errno == ECONNREFUSED
 	      || errno == EPFNOSUPPORT
 	      || errno == EAFNOSUPPORT)
@@ -142,6 +147,7 @@ _nss_dns_getnetbyname_r (const char *name, struct netent *result,
 			errnop, herrnop, BYNAME);
   if (net_buffer.buf != orig_net_buffer)
     free (net_buffer.buf);
+  __resolv_context_put (ctx);
   return status;
 }
 
@@ -169,7 +175,8 @@ _nss_dns_getnetbyaddr_r (uint32_t net, int type, struct netent *result,
   if (type != AF_INET)
     return NSS_STATUS_UNAVAIL;
 
-  if (__res_maybe_init (&_res, 0) == -1)
+  struct resolv_context *ctx = __resolv_context_get ();
+  if (ctx == NULL)
     {
       *errnop = errno;
       *herrnop = NETDB_INTERNAL;
@@ -204,8 +211,8 @@ _nss_dns_getnetbyaddr_r (uint32_t net, int type, struct netent *result,
 
   net_buffer.buf = orig_net_buffer = (querybuf *) alloca (1024);
 
-  anslen = __libc_res_nquery (&_res, qbuf, C_IN, T_PTR, net_buffer.buf->buf,
-			      1024, &net_buffer.ptr, NULL, NULL, NULL, NULL);
+  anslen = __res_context_query (ctx, qbuf, C_IN, T_PTR, net_buffer.buf->buf,
+				1024, &net_buffer.ptr, NULL, NULL, NULL, NULL);
   if (anslen < 0)
     {
       /* Nothing found.  */
@@ -213,6 +220,7 @@ _nss_dns_getnetbyaddr_r (uint32_t net, int type, struct netent *result,
       __set_errno (olderr);
       if (net_buffer.buf != orig_net_buffer)
 	free (net_buffer.buf);
+      __resolv_context_put (ctx);
       return (err == ECONNREFUSED
 	      || err == EPFNOSUPPORT
 	      || err == EAFNOSUPPORT)
@@ -233,6 +241,7 @@ _nss_dns_getnetbyaddr_r (uint32_t net, int type, struct netent *result,
       result->n_net = u_net;
     }
 
+  __resolv_context_put (ctx);
   return status;
 }