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.
2025-12-19 10:18:25 +00:00 · 2014-12-10 17:32:16 +00:00
parent b9ff5c8f43
commit 193de4abf5
5 changed files with 137 additions and 5 deletions
--- a/src/inotify.c
+++ b/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
+
+  
+