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[PATCH] Change res_init to take (lazilly) effect in all threads


Hi!

The following (so far only lightly tested) patch changes res_init (), so
that when an application calls it, all threads the next time they try to
use their _res structures re-initialize themselves too.
The struct __res_state addition of a long long counter is a little bit
complicated, because on 64-bit arches sizeof (_res._u._ext) was already
48 bytes and _res._u.pad is 52 bytes.  Fortunately the whole _res
is 568 bytes big and thus the counter can be partly in the previous tail
padding of the whole structure.
On 32-bit arches, the aligned attribute is needed, because otherwise the
whole _u union could be moved by 4 bytes, which is not desirable.
As a testcase I used:
#define _GNU_SOURCE
#include <pthread.h>
#include <netdb.h>
#include <resolv.h>

pthread_barrier_t b;
void *tf (void *arg)
{
  int i;
  for (i = 0; i < 3; ++i)
    gethostbyname ("www.redhat.com");
  pthread_barrier_wait (&b);
  pthread_barrier_wait (&b);
  for (i = 0; i < 3; ++i)
    gethostbyname ("www.redhat.com");
  pthread_barrier_wait (&b);
  pthread_barrier_wait (&b);
  for (i = 0; i < 3; ++i)
    gethostbyname ("www.redhat.com");
}

int main (void)
{
  pthread_t p[2];
  int i;
  pthread_barrier_init (&b, NULL, 3);
  pthread_create (&p[0], NULL, tf, NULL);
  pthread_create (&p[1], NULL, tf, NULL);
  for (i = 0; i < 3; ++i)
    gethostbyname ("www.redhat.com");
  pthread_barrier_wait (&b);
  res_init ();
  pthread_barrier_wait (&b);
  for (i = 0; i < 3; ++i)
    gethostbyname ("www.redhat.com");
  pthread_barrier_wait (&b);
  res_init ();
  pthread_barrier_wait (&b);
  for (i = 0; i < 3; ++i)
    gethostbyname ("www.redhat.com");
  pthread_join (p[0], NULL);
  pthread_join (p[1], NULL);
  return 0;
}
and straced it how many resolv.conf opens were done (should be 9, without this
patch just 5).

2004-08-04  Jakub Jelinek  <jakub@redhat.com>

	* hesiod/hesiod.c (__hesiod_res_get): Use calloc instead of malloc +
	memset.
	(__hesiod_res_set): Free nsaddrs.

	* include/resolv.h (__res_maybe_init): Add prototype.
	* resolv/resolv.h (struct __res_state): Add _u._ext.initstamp field.
	* resolv/Versions (libc): Add __res_maybe_init@@GLIBC_PRIVATE.
	* resolv/res_libc.c (__res_initstamp, lock): New variables.
	(res_init): Increase __res_initstamp.
	(__res_maybe_init): New function.
	* resolv/res_init.c (__res_vinit): Initialize _u._ext.initstamp.
	* hesiod/hesiod.c (__hesiod_res_get): Use __res_maybe_init instead
	of RES_INIT check and {res_ninit,__res_ninit,res_init} call.
	* sysdeps/posix/getaddrinfo.c (gaih_inet): Likewise.
	* resolv/nss_dns/dns-host.c (_nss_dns_gethostbyname2_r,
	_nss_dns_gethostbyaddr_r): Likewise.
	* resolv/nss_dns/dns-network.c (_nss_dns_getnetbyname_r,
	_nss_dns_getnetbyaddr_r): Likewise.
	* resolv/gethnamaddr.c (gethostbyname, gethostbyname2,
	gethostbyaddr): Likewise.
	* resolv/res_data.c (fp_nquery, res_mkquery, res_mkupdate,
	res_isourserver, res_sendsigned, res_update, res_search,
	res_querydomain): Likewise.
	* nss/getXXbyYY_r.c (INTERNAL (REENTRANT_NAME)): Likewise.
	* nss/digits_dots.c (__nss_hostname_digits_dots): Likewise.
	* nss/getnssent_r.c (__nss_setent, __nss_endent, __nss_getent_r):
	Likewise.

--- libc/hesiod/hesiod.c.jj	2004-08-04 14:42:20.000000000 +0200
+++ libc/hesiod/hesiod.c	2004-08-04 14:54:25.000000000 +0200
@@ -448,10 +448,9 @@ __hesiod_res_get(void *context) {
 
 	if (!ctx->res) {
 		struct __res_state *res;
-		res = (struct __res_state *)malloc(sizeof *res);
+		res = (struct __res_state *)calloc(1, sizeof *res);
 		if (res == NULL)
 			return (NULL);
-		memset(res, 0, sizeof *res);
 		__hesiod_res_set(ctx, res, free);
 	}
 
@@ -465,6 +464,12 @@ __hesiod_res_set(void *context, struct _
 
 	if (ctx->res && ctx->free_res) {
 		res_nclose(ctx->res);
+		if ((ctx->res->options & RES_INIT) && ctx->res->nscount > 0) {
+			for (int ns = 0; ns < MAXNS; ns++) {
+				free (ctx->res->_u._ext.nsaddrs[ns]);
+				ctx->res->_u._ext.nsaddrs[ns] = NULL;
+			}
+		}
 		(*ctx->free_res)(ctx->res);
 	}
 
@@ -478,8 +483,7 @@ init(struct hesiod_p *ctx) {
 	if (!ctx->res && !__hesiod_res_get(ctx))
 		return (-1);
 
-	if (((ctx->res->options & RES_INIT) == 0) &&
-	    (res_ninit(ctx->res) == -1))
+	if (__res_maybe_init (ctx->res, 0) == -1)
 		return (-1);
 
 	return (0);
--- libc/sysdeps/posix/getaddrinfo.c.jj	2004-08-04 14:42:26.000000000 +0200
+++ libc/sysdeps/posix/getaddrinfo.c	2004-08-04 14:54:25.563908498 +0200
@@ -661,7 +661,7 @@ gaih_inet (const char *name, const struc
 		no_more = __nss_database_lookup ("hosts", NULL,
 						 "dns [!UNAVAIL=return] files", &nip);
 
-	      if ((_res.options & RES_INIT) == 0 && __res_ninit(&_res) == -1)
+	      if (__res_maybe_init (&_res, 0) == -1)
 		no_more = 1;
 	      old_res_options = _res.options;
 	      _res.options &= ~RES_USE_INET6;
--- libc/include/resolv.h.jj	2004-08-04 14:42:20.000000000 +0200
+++ libc/include/resolv.h	2004-08-04 14:54:25.564908322 +0200
@@ -31,6 +31,7 @@ extern struct __res_state _res;
 
 /* Now define the internal interfaces.  */
 extern int __res_vinit (res_state, int);
+extern int __res_maybe_init (res_state, int);
 extern void _sethtent (int);
 extern void _endhtent (void);
 extern struct hostent *_gethtent (void);
@@ -46,6 +47,7 @@ extern void res_send_setrhook (res_send_
 extern int res_ourserver_p (const res_state __statp,
 			    const struct sockaddr_in6 *__inp);
 libc_hidden_proto (__res_ninit)
+libc_hidden_proto (__res_maybe_init)
 libc_hidden_proto (__res_nclose)
 libc_hidden_proto (__res_randomid)
 libc_hidden_proto (__res_state)
--- libc/resolv/nss_dns/dns-host.c.jj	2004-08-04 14:42:23.000000000 +0200
+++ libc/resolv/nss_dns/dns-host.c	2004-08-04 14:54:25.000000000 +0200
@@ -145,7 +145,7 @@ _nss_dns_gethostbyname2_r (const char *n
   int olderr = errno;
   enum nss_status status;
 
-  if ((_res.options & RES_INIT) == 0 && __res_ninit (&_res) == -1)
+  if (__res_maybe_init (&_res, 0) == -1)
     return NSS_STATUS_UNAVAIL;
 
   switch (af) {
@@ -263,7 +263,7 @@ _nss_dns_gethostbyaddr_r (const void *ad
   int n, status;
   int olderr = errno;
 
-  if ((_res.options & RES_INIT) == 0 && __res_ninit (&_res) == -1)
+  if (__res_maybe_init (&_res, 0) == -1)
     return NSS_STATUS_UNAVAIL;
 
   if (af == AF_INET6 && len == IN6ADDRSZ
--- libc/resolv/nss_dns/dns-network.c.jj	2004-08-04 14:42:23.000000000 +0200
+++ libc/resolv/nss_dns/dns-network.c	2004-08-04 14:54:25.000000000 +0200
@@ -1,4 +1,5 @@
-/* Copyright (C) 1996, 1997, 1998, 1999, 2002 Free Software Foundation, Inc.
+/* Copyright (C) 1996, 1997, 1998, 1999, 2002, 2004
+   Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Extended from original form by Ulrich Drepper <drepper@cygnus.com>, 1996.
 
@@ -120,7 +121,7 @@ _nss_dns_getnetbyname_r (const char *nam
   char *qbuf;
   enum nss_status status;
 
-  if ((_res.options & RES_INIT) == 0 && __res_ninit (&_res) == -1)
+  if (__res_maybe_init (&_res, 0) == -1)
     return NSS_STATUS_UNAVAIL;
 
   qbuf = strdupa (name);
@@ -171,7 +172,7 @@ _nss_dns_getnetbyaddr_r (uint32_t net, i
   if (type != AF_INET)
     return NSS_STATUS_UNAVAIL;
 
-  if ((_res.options & RES_INIT) == 0 && __res_ninit (&_res) == -1)
+  if (__res_maybe_init (&_res, 0) == -1)
     return NSS_STATUS_UNAVAIL;
 
   net2 = (u_int32_t) net;
--- libc/resolv/gethnamaddr.c.jj	2004-08-04 14:42:23.000000000 +0200
+++ libc/resolv/gethnamaddr.c	2004-08-04 14:54:25.000000000 +0200
@@ -493,10 +493,10 @@ gethostbyname(name)
 {
 	struct hostent *hp;
 
-	if ((_res.options & RES_INIT) == 0 && __res_ninit(&_res) == -1) {
+	if (__res_maybe_init (&_res, 0) == -1) {
 		__set_h_errno (NETDB_INTERNAL);
 		return (NULL);
-       }
+	}
 	if (_res.options & RES_USE_INET6) {
 		hp = gethostbyname2(name, AF_INET6);
 		if (hp)
@@ -522,7 +522,7 @@ gethostbyname2(name, af)
 	struct hostent *ret;
 	extern struct hostent *_gethtbyname2();
 
-	if ((_res.options & RES_INIT) == 0 && __res_ninit(&_res) == -1) {
+	if (__res_maybe_init (&_res, 0) == -1) {
 		__set_h_errno (NETDB_INTERNAL);
 		return (NULL);
 	}
@@ -665,7 +665,7 @@ gethostbyaddr(addr, len, af)
 #endif /*SUNSECURITY*/
 	extern struct hostent *_gethtbyaddr();
 
-	if ((_res.options & RES_INIT) == 0 && __res_ninit(&_res) == -1) {
+	if (__res_maybe_init (&_res, 0) == -1) {
 		__set_h_errno (NETDB_INTERNAL);
 		return (NULL);
 	}
--- libc/resolv/res_data.c.jj	2004-08-04 14:42:23.000000000 +0200
+++ libc/resolv/res_data.c	2004-08-04 14:54:25.000000000 +0200
@@ -141,7 +141,7 @@ fp_query(const u_char *msg, FILE *file) 
 
 void
 fp_nquery(const u_char *msg, int len, FILE *file) {
-	if ((_res.options & RES_INIT) == 0 && __res_ninit(&_res) == -1)
+	if (__res_maybe_init (&_res, 0) == -1)
 		return;
 
 	res_pquery(&_res, msg, len, file);
@@ -157,7 +157,7 @@ res_mkquery(int op,			/* opcode of query
 	    u_char *buf,		/* buffer to put query */
 	    int buflen)			/* size of buffer */
 {
-	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
+	if (__res_maybe_init (&_res, 1) == -1) {
 		RES_SET_H_ERRNO(&_res, NETDB_INTERNAL);
 		return (-1);
 	}
@@ -169,7 +169,7 @@ res_mkquery(int op,			/* opcode of query
 #ifdef BIND_UPDATE
 int
 res_mkupdate(ns_updrec *rrecp_in, u_char *buf, int buflen) {
-	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
+	if (__res_maybe_init (&_res, 1) == -1) {
 		RES_SET_H_ERRNO(&_res, NETDB_INTERNAL);
 		return (-1);
 	}
@@ -184,7 +184,7 @@ res_query(const char *name,	/* domain na
 	  u_char *answer,	/* buffer to put answer */
 	  int anslen)		/* size of answer buffer */
 {
-	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
+	if (__res_maybe_init (&_res, 1) == -1) {
 		RES_SET_H_ERRNO(&_res, NETDB_INTERNAL);
 		return (-1);
 	}
@@ -208,7 +208,7 @@ res_isourserver(const struct sockaddr_in
 
 int
 res_send(const u_char *buf, int buflen, u_char *ans, int anssiz) {
-	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
+	if (__res_maybe_init (&_res, 1) == -1) {
 		/* errno should have been set by res_init() in this case. */
 		return (-1);
 	}
@@ -221,7 +221,7 @@ int
 res_sendsigned(const u_char *buf, int buflen, ns_tsig_key *key,
 	       u_char *ans, int anssiz)
 {
-	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
+	if (__res_maybe_init (&_res, 1) == -1) {
 		/* errno should have been set by res_init() in this case. */
 		return (-1);
 	}
@@ -249,7 +249,7 @@ res_close(void) {
 #ifdef BIND_UPDATE
 int
 res_update(ns_updrec *rrecp_in) {
-	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
+	if (__res_maybe_init (&_res, 1) == -1) {
 		RES_SET_H_ERRNO(&_res, NETDB_INTERNAL);
 		return (-1);
 	}
@@ -264,7 +264,7 @@ res_search(const char *name,	/* domain n
 	   u_char *answer,	/* buffer to put answer */
 	   int anslen)		/* size of answer */
 {
-	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
+	if (__res_maybe_init (&_res, 1) == -1) {
 		RES_SET_H_ERRNO(&_res, NETDB_INTERNAL);
 		return (-1);
 	}
@@ -279,7 +279,7 @@ res_querydomain(const char *name,
 		u_char *answer,		/* buffer to put answer */
 		int anslen)		/* size of answer */
 {
-	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
+	if (__res_maybe_init (&_res, 1) == -1) {
 		RES_SET_H_ERRNO(&_res, NETDB_INTERNAL);
 		return (-1);
 	}
--- libc/resolv/resolv.h.jj	2004-08-04 14:42:23.000000000 +0200
+++ libc/resolv/resolv.h	2004-08-04 14:54:25.568907618 +0200
@@ -134,6 +134,12 @@ struct __res_state {
 			u_int16_t		nscount6;
 			u_int16_t		nsinit;
 			struct sockaddr_in6	*nsaddrs[MAXNS];
+#ifdef _LIBC
+			unsigned long long int	initstamp
+			  __attribute__((aligned (sizeof (long))));
+#else
+			unsigned int		_initstamp[2];
+#endif
 		} _ext;
 	} _u;
 };
--- libc/resolv/res_init.c.jj	2004-08-04 14:42:23.000000000 +0200
+++ libc/resolv/res_init.c	2004-08-04 14:54:25.567907794 +0200
@@ -161,6 +161,10 @@ __res_vinit(res_state statp, int preinit
 #ifndef RFC1535
 	int dots;
 #endif
+#ifdef _LIBC
+	extern unsigned long long int __res_initstamp attribute_hidden;
+	statp->_u._ext.initstamp = __res_initstamp;
+#endif
 
 	if (!preinit) {
 		statp->retrans = RES_TIMEOUT;
--- libc/resolv/Versions.jj	2004-08-04 14:42:22.000000000 +0200
+++ libc/resolv/Versions	2004-08-04 14:54:25.570907266 +0200
@@ -38,6 +38,8 @@ libc {
     # This version is for the TLS symbol, GLIBC_2.0 is the old object symbol.
     h_errno; __resp;
 %endif
+
+    __res_maybe_init;
   }
 }
 
--- libc/resolv/res_libc.c.jj	2004-08-04 14:42:23.000000000 +0200
+++ libc/resolv/res_libc.c	2004-08-04 15:36:12.104626490 +0200
@@ -19,12 +19,16 @@
 #include <netinet/in.h>
 #include <arpa/nameser.h>
 #include <resolv.h>
+#include <bits/libc-lock.h>
 
 
 /* The following bit is copied from res_data.c (where it is #ifdef'ed
    out) since res_init() should go into libc.so but the rest of that
    file should not.  */
 
+unsigned long long int __res_initstamp attribute_hidden;
+__libc_lock_define_initialized (static, lock);
+
 int
 res_init(void) {
 	extern int __res_vinit(res_state, int);
@@ -70,8 +74,45 @@ res_init(void) {
 	if (!_res.id)
 		_res.id = res_randomid();
 
+	__libc_lock_lock (lock);
+	/* Request all threads to re-initialize their resolver states,
+	   resolv.conf might have changed.  */
+	__res_initstamp++;
+	__libc_lock_unlock (lock);
+
 	return (__res_vinit(&_res, 1));
 }
+
+/* Initialize resp if RES_INIT is not yet set or if res_init in some other
+   thread requested re-initializing.  */
+int
+__res_maybe_init (res_state resp, int preinit)
+{
+	if (resp->options & RES_INIT) {
+		if (__res_initstamp != resp->_u._ext.initstamp) {
+			if (resp->nscount > 0) {
+				__res_nclose (resp);
+				for (int ns = 0; ns < MAXNS; ns++) {
+					free (resp->_u._ext.nsaddrs[ns]);
+					resp->_u._ext.nsaddrs[ns] = NULL;
+				}
+				return __res_vinit (resp, 1);
+			}
+		}
+		return 0;
+	} else if (preinit) {
+		if (!resp->retrans)
+			resp->retrans = RES_TIMEOUT;
+		if (!resp->retry)
+			resp->retry = 4;
+		resp->options = RES_DEFAULT;
+		if (!resp->id)
+			resp->id = res_randomid ();
+		return __res_vinit (resp, 1);
+	} else
+		return __res_ninit (resp);
+}
+libc_hidden_def (__res_maybe_init)
 
 /* This needs to be after the use of _res in res_init, above.  */
 #undef _res
--- libc/nss/getXXbyYY_r.c.jj	2004-08-04 14:42:22.000000000 +0200
+++ libc/nss/getXXbyYY_r.c	2004-08-04 14:54:25.573906738 +0200
@@ -182,7 +182,7 @@ INTERNAL (REENTRANT_NAME) (ADD_PARAMS, L
 #ifdef NEED__RES
 	  /* The resolver code will really be used so we have to
 	     initialize it.  */
-	  if ((_res.options & RES_INIT) == 0 && __res_ninit (&_res) == -1)
+	  if (__res_maybe_init (&_res, 0) == -1)
 	    {
 	      *h_errnop = NETDB_INTERNAL;
 	      *result = NULL;
--- libc/nss/digits_dots.c.jj	2004-08-04 14:42:22.000000000 +0200
+++ libc/nss/digits_dots.c	2004-08-04 14:54:25.571907090 +0200
@@ -43,7 +43,7 @@ __nss_hostname_digits_dots (const char *
 
   /* We have to test for the use of IPv6 which can only be done by
      examining `_res'.  */
-  if ((_res.options & RES_INIT) == 0 && __res_ninit (&_res) == -1)
+  if (__res_maybe_init (&_res, 0) == -1)
     {
       if (h_errnop)
 	*h_errnop = NETDB_INTERNAL;
--- libc/nss/getnssent_r.c.jj	2004-08-04 14:42:22.000000000 +0200
+++ libc/nss/getnssent_r.c	2004-08-04 14:54:25.572906914 +0200
@@ -1,4 +1,4 @@
-/* Copyright (C) 2000,02 Free Software Foundation, Inc.
+/* Copyright (C) 2000, 2002, 2004 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
@@ -60,8 +60,7 @@ __nss_setent (const char *func_name, db_
   } fct;
   int no_more;
 
-  if (res && (_res.options & RES_INIT) == 0
-      && __res_ninit (&_res) == -1)
+  if (res && __res_maybe_init (&_res, 0) == -1)
     {
       __set_h_errno (NETDB_INTERNAL);
       return;
@@ -104,8 +103,7 @@ __nss_endent (const char *func_name, db_
   } fct;
   int no_more;
 
-  if (res && (_res.options & RES_INIT) == 0
-      && __res_ninit (&_res) == -1)
+  if (res && __res_maybe_init (&_res, 0) == -1)
     {
       __set_h_errno (NETDB_INTERNAL);
       return;
@@ -145,8 +143,7 @@ __nss_getent_r (const char *getent_func_
   int no_more;
   enum nss_status status;
 
-  if (res && (_res.options & RES_INIT) == 0
-      && __res_ninit (&_res) == -1)
+  if (res && __res_maybe_init (&_res, 0) == -1)
     {
       *h_errnop = NETDB_INTERNAL;
       *result = NULL;

	Jakub


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