Use inotify instead of polling on Linux.

This should solve problems people are seeing when a file changes
twice within a second and thus is missed for polling.

src/dnsmasq.c

@@ -315,9 +315,15 @@ int main (int argc, char **argv)
   if (daemon->port != 0)
     {
       cache_init();
+
 #ifdef HAVE_DNSSEC
       blockdata_init();
 #endif
+
+#ifdef HAVE_LINUX_NETWORK
+      if (!option_bool(OPT_NO_POLL))
+	inotify_dnsmasq_init();
+#endif
     }
     
   if (option_bool(OPT_DBUS))
@@ -793,6 +799,11 @@ int main (int argc, char **argv)
   
   pid = getpid();
   
+#ifdef HAVE_LINUX_NETWORK
+  /* Using inotify, have to select a resolv file at startup */
+  poll_resolv(1, 0, now);
+#endif
+  
   while (1)
     {
       int maxfd = -1;
@@ -862,11 +873,16 @@ int main (int argc, char **argv)
 #if defined(HAVE_LINUX_NETWORK)
       FD_SET(daemon->netlinkfd, &rset);
       bump_maxfd(daemon->netlinkfd, &maxfd);
+      if (daemon->port != 0 && !option_bool(OPT_NO_POLL))
+	{
+	  FD_SET(daemon->inotifyfd, &rset);
+	  bump_maxfd(daemon->inotifyfd, &maxfd);
+	}
 #elif defined(HAVE_BSD_NETWORK)
       FD_SET(daemon->routefd, &rset);
       bump_maxfd(daemon->routefd, &maxfd);
 #endif
-
+      
       FD_SET(piperead, &rset);
       bump_maxfd(piperead, &maxfd);
 
@@ -929,6 +945,10 @@ int main (int argc, char **argv)
 	route_sock();
 #endif
 
+#ifdef HAVE_LINUX_NETWORK
+      if (daemon->port != 0 && !option_bool(OPT_NO_POLL) && FD_ISSET(daemon->inotifyfd, &rset) && inotify_check())
+	poll_resolv(1, 1, now); 	  
+#else
       /* Check for changes to resolv files once per second max. */
       /* Don't go silent for long periods if the clock goes backwards. */
       if (daemon->last_resolv == 0 || 
@@ -941,7 +961,8 @@ int main (int argc, char **argv)
 	  poll_resolv(0, daemon->last_resolv != 0, now); 	  
 	  daemon->last_resolv = now;
 	}
-      
+#endif
+
       if (FD_ISSET(piperead, &rset))
 	async_event(piperead, now);
       

src/dnsmasq.h

@@ -541,6 +541,10 @@ struct resolvc {
   int is_default, logged;
   time_t mtime;
   char *name;
+#ifdef HAVE_LINUX_NETWORK
+  int wd; /* inotify watch descriptor */
+  char *file; /* pointer to file part if path */
+#endif
 };
 
 /* adn-hosts parms from command-line (also dhcp-hostsfile and dhcp-optsfile */
@@ -998,7 +1002,7 @@ extern struct daemon {
   /* DHCP state */
   int dhcpfd, helperfd, pxefd; 
 #if defined(HAVE_LINUX_NETWORK)
-  int netlinkfd;
+  int netlinkfd, inotifyfd;
 #elif defined(HAVE_BSD_NETWORK)
   int dhcp_raw_fd, dhcp_icmp_fd, routefd;
 #endif
@@ -1469,3 +1473,8 @@ void loop_send_probes();
 int detect_loop(char *query, int type);
 #endif
 
+/* inotify.c */
+#ifdef HAVE_LINUX_NETWORK
+void inotify_dnsmasq_init();
+int inotify_check(void);
+#endif

src/inotify.c

@@ -0,0 +1,102 @@
+/* dnsmasq is Copyright (c) 2000-2014 Simon Kelley
+ 
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 dated June, 1991, or
+   (at your option) version 3 dated 29 June, 2007.
+ 
+   This program 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 General Public License for more details.
+     
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "dnsmasq.h"
+#include <sys/inotify.h>
+
+#ifdef HAVE_LINUX_NETWORK
+
+/* the strategy is to set a inotify on the directories containing
+   resolv files, for any files in the directory which are close-write 
+   or moved into the directory.
+   
+   When either of those happen, we look to see if the file involved
+   is actually a resolv-file, and if so, call poll-resolv with
+   the "force" argument, to ensure it's read.
+
+   This adds one new error condition: the directories containing
+   all specified resolv-files must exist at start-up, even if the actual
+   files don't. 
+*/
+
+static char *inotify_buffer;
+#define INOTIFY_SZ (sizeof(struct inotify_event) + NAME_MAX + 1)
+
+void inotify_dnsmasq_init()
+{
+  struct resolvc *res;
+
+  inotify_buffer = safe_malloc(INOTIFY_SZ);
+
+  daemon->inotifyfd = inotify_init1(IN_NONBLOCK | IN_CLOEXEC);
+
+  if (daemon->inotifyfd == -1)
+    die(_("failed to create inotify: %s"), NULL, EC_MISC);
+
+  for (res = daemon->resolv_files; res; res = res->next)
+    {
+      char *d = strrchr(res->name, '/');
+      
+      if (!d)
+	die(_("resolv-file %s not an absolute path"), res->name, EC_MISC);
+       
+      *d = 0; /* make ->name just directory */
+      res->wd = inotify_add_watch(daemon->inotifyfd, res->name, IN_CLOSE_WRITE | IN_MOVED_TO);
+      res->file = d+1; /* pointer to filename */
+      
+      if (res->wd == -1 && errno == ENOENT)
+	die(_("directory %s for resolv-file is missing, cannot poll"), res->name, EC_MISC);
+      
+      *d = '/'; /* restore name */
+      
+      if (res->wd == -1)
+	die(_("failed to create inotify for %s: %s"), res->name, EC_MISC);
+    }
+}
+
+int inotify_check(void)
+{
+  int hit = 0;
+  
+  while (1)
+    {
+      int rc;
+      char *p;
+      struct resolvc *res;
+      struct inotify_event *in;
+
+      while ((rc = read(daemon->inotifyfd, inotify_buffer, INOTIFY_SZ)) == -1 && errno == EINTR);
+      
+      if (rc <= 0)
+	break;
+      
+      for (p = inotify_buffer; rc - (p - inotify_buffer) >= (int)sizeof(struct inotify_event); p += sizeof(struct inotify_event) + in->len) 
+	{
+	  in = (struct inotify_event*)p;
+	  
+	  for (res = daemon->resolv_files; res; res = res->next)
+	    if (res->wd == in->wd && in->len != 0 && strcmp(res->file, in->name) == 0)
+	      hit = 1;
+	}
+    }
+
+  return hit;
+}
+
+#endif
+
+  
+