Cache network interface information

Whenever getaddrinfo needed network interface information it used the
netlink interface to read the information every single time.  The
problem is that this information can change at any time.

The patch implements monitoring of the network interfaces through
nscd.  If no change is detected the previously read information can
be reused (which is the norm).  This timestamp information is also
made available to other processes using the shared memory segment
between nscd and those processes.

1 files changed, 143 insertions, 32 deletions

diff --git a/sysdeps/unix/sysv/linux/check_pf.c b/sysdeps/unix/sysv/linux/check_pf.c
index d5ad7ea..1f66684 100644
--- a/sysdeps/unix/sysv/linux/check_pf.c
+++ b/sysdeps/unix/sysv/linux/check_pf.c
@@ -1,5 +1,5 @@
 /* Determine protocol families for which interfaces exist.  Linux version.
-   Copyright (C) 2003, 2006, 2007, 2008, 2010, 2011 Free Software Foundation, Inc.
+   Copyright (C) 2003, 2006-2008, 2010, 2011 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
@@ -33,6 +33,9 @@
 
 #include <not-cancel.h>
 #include <kernel-features.h>
+#include <bits/libc-lock.h>
+#include <atomic.h>
+#include <nscd/nscd-client.h>
 
 
 #ifndef IFA_F_HOMEADDRESS
@@ -43,9 +46,42 @@
 #endif
 
 
-static int
-make_request (int fd, pid_t pid, bool *seen_ipv4, bool *seen_ipv6,
-	      struct in6addrinfo **in6ai, size_t *in6ailen)
+struct cached_data
+{
+  uint32_t timestamp;
+  uint32_t usecnt;
+  bool seen_ipv4;
+  bool seen_ipv6;
+  size_t in6ailen;
+  struct in6addrinfo in6ai[0];
+};
+
+static struct cached_data noai6ai_cached =
+  {
+    .usecnt = 3,	/* Make sure we never try to delete this entry.  */
+    .in6ailen = 0
+  };
+
+static struct cached_data *cache;
+__libc_lock_define_initialized (static, lock);
+
+
+#ifdef IS_IN_nscd
+static uint32_t nl_timestamp;
+
+uint32_t
+__bump_nl_timestamp (void)
+{
+  if (atomic_increment_val (&nl_timestamp) == 0)
+    atomic_increment (&nl_timestamp);
+
+  return nl_timestamp;
+}
+#endif
+
+
+static struct cached_data *
+make_request (int fd, pid_t pid)
 {
   struct req
   {
@@ -99,9 +135,6 @@ make_request (int fd, pid_t pid, bool *seen_ipv4, bool *seen_ipv6,
 				    sizeof (nladdr))) < 0)
     goto out_fail;
 
-  *seen_ipv4 = false;
-  *seen_ipv6 = false;
-
   bool done = false;
   struct in6ailist
   {
@@ -109,6 +142,8 @@ make_request (int fd, pid_t pid, bool *seen_ipv4, bool *seen_ipv6,
     struct in6ailist *next;
   } *in6ailist = NULL;
   size_t in6ailistlen = 0;
+  bool seen_ipv4 = false;
+  bool seen_ipv6 = false;
 
   do
     {
@@ -172,12 +207,12 @@ make_request (int fd, pid_t pid, bool *seen_ipv4, bool *seen_ipv6,
 		    {
 		      if (*(const in_addr_t *) address
 			  != htonl (INADDR_LOOPBACK))
-			*seen_ipv4 = true;
+			seen_ipv4 = true;
 		    }
 		  else
 		    {
 		      if (!IN6_IS_ADDR_LOOPBACK (address))
-			*seen_ipv6 = true;
+			seen_ipv6 = true;
 		    }
 		}
 
@@ -211,30 +246,46 @@ make_request (int fd, pid_t pid, bool *seen_ipv4, bool *seen_ipv6,
     }
   while (! done);
 
-  if (*seen_ipv6 && in6ailist != NULL)
+  struct cached_data *result;
+  if (seen_ipv6 && in6ailist != NULL)
     {
-      *in6ai = malloc (in6ailistlen * sizeof (**in6ai));
-      if (*in6ai == NULL)
+      result = malloc (sizeof (*result)
+		       + in6ailistlen * sizeof (struct in6addrinfo));
+      if (result == NULL)
 	goto out_fail;
 
-      *in6ailen = in6ailistlen;
+#ifdef IS_IN_nscd
+      result->timestamp = nl_timestamp;
+#else
+      result->timestamp = __nscd_get_nl_timestamp ();
+#endif
+      result->usecnt = 2;
+      result->seen_ipv4 = seen_ipv4;
+      result->seen_ipv6 = true;
+      result->in6ailen = in6ailistlen;
 
       do
 	{
-	  (*in6ai)[--in6ailistlen] = in6ailist->info;
+	  result->in6ai[--in6ailistlen] = in6ailist->info;
 	  in6ailist = in6ailist->next;
 	}
       while (in6ailist != NULL);
     }
+  else
+    {
+      noai6ai_cached.seen_ipv4 = seen_ipv4;
+      noai6ai_cached.seen_ipv6 = seen_ipv6;
+      result = &noai6ai_cached;
+    }
 
   if (use_malloc)
     free (buf);
-  return 0;
+  return result;
 
 out_fail:
   if (use_malloc)
     free (buf);
-  return -1;
+  return NULL;
 }
 
 
@@ -258,28 +309,65 @@ __check_pf (bool *seen_ipv4, bool *seen_ipv6,
 
   if (! __no_netlink_support)
     {
-      int fd = __socket (PF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+      struct cached_data *olddata = NULL;
+      struct cached_data *data = NULL;
 
-      if (__builtin_expect (fd >= 0, 1))
+      __libc_lock_lock (lock);
+
+#ifdef IS_IN_nscd
+# define cache_valid() nl_timestamp != 0 && cache->timestamp == nl_timestamp
+#else
+# define cache_valid() \
+      ({ uint32_t val = __nscd_get_nl_timestamp ();			      \
+	 val != 0 && cache->timestamp == val; })
+#endif
+      if (cache != NULL && cache_valid ())
+	{
+	  data = cache;
+	  atomic_increment (&cache->usecnt);
+	}
+      else
 	{
-	  struct sockaddr_nl nladdr;
-	  memset (&nladdr, '\0', sizeof (nladdr));
-	  nladdr.nl_family = AF_NETLINK;
+	  int fd = __socket (PF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
 
-	  socklen_t addr_len = sizeof (nladdr);
+	  if (__builtin_expect (fd >= 0, 1))
+	    {
+	      struct sockaddr_nl nladdr;
+	      memset (&nladdr, '\0', sizeof (nladdr));
+	      nladdr.nl_family = AF_NETLINK;
+
+	      socklen_t addr_len = sizeof (nladdr);
+
+	      if(__bind (fd, (struct sockaddr *) &nladdr, sizeof (nladdr)) == 0
+		 && __getsockname (fd, (struct sockaddr *) &nladdr,
+				   &addr_len) == 0)
+		data = make_request (fd, nladdr.nl_pid);
+
+	      close_not_cancel_no_status (fd);
+	    }
+
+	  if (data != NULL)
+	    {
+	      olddata = cache;
+	      cache = data;
+	    }
+	}
 
-	  bool success
-	    = (__bind (fd, (struct sockaddr *) &nladdr, sizeof (nladdr)) == 0
-	       && __getsockname (fd, (struct sockaddr *) &nladdr,
-				 &addr_len) == 0
-	       && make_request (fd, nladdr.nl_pid, seen_ipv4, seen_ipv6,
-				in6ai, in6ailen) == 0);
+      __libc_lock_unlock (lock);
 
-	  close_not_cancel_no_status (fd);
+      if (data != NULL)
+	{
+	  /* It worked.  */
+	  *seen_ipv4 = data->seen_ipv4;
+	  *seen_ipv6 = data->seen_ipv6;
+	  *in6ailen = data->in6ailen;
+	  *in6ai = data->in6ai;
+
+	  if (olddata != NULL && olddata->usecnt > 0
+	      && atomic_add_zero (&olddata->usecnt, -1))
+	    free (olddata);
 
-	  if (success)
-	    /* It worked.  */
-	    return;
+	  return;
 	}
 
 #if __ASSUME_NETLINK_SUPPORT == 0
@@ -318,3 +406,26 @@ __check_pf (bool *seen_ipv4, bool *seen_ipv6,
   (void) freeifaddrs (ifa);
 #endif
 }
+
+
+void
+__free_in6ai (struct in6addrinfo *ai)
+{
+  if (ai != NULL)
+    {
+      struct cached_data *data =
+	(struct cached_data *) ((char *) ai
+				- offsetof (struct cached_data, in6ai));
+
+      if (atomic_add_zero (&data->usecnt, -1))
+	{
+	  __libc_lock_lock (lock);
+
+	  if (data->usecnt == 0)
+	    /* Still unused.  */
+	    free (data);
+
+	  __libc_lock_unlock (lock);
+	}
+    }
+}