src/inotify.c

/* 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"
#ifdef HAVE_LINUX_NETWORK

#include <sys/inotify.h>

#ifdef HAVE_DHCP
static void check_for_dhcp_inotify(struct inotify_event *in, time_t now);
#endif


/* 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 = NULL, *path;
      
      if (!(path = realpath(res->name, NULL)))
	{
	  /* realpath will fail if the file doesn't exist, but
	     dnsmasq copes with missing files, so fall back 
	     and assume that symlinks are not in use in that case. */
	  if (errno == ENOENT)
	    path = res->name;
	  else
	    die(_("cannot cannonicalise resolv-file %s: %s"), res->name, EC_MISC); 
	}
      
      if ((d = strrchr(path, '/')))
	{
	  *d = 0; /* make path just directory */
	  res->wd = inotify_add_watch(daemon->inotifyfd, path, IN_CLOSE_WRITE | IN_MOVED_TO);

	  res->file = d+1; /* pointer to filename */
	  *d = '/';
	  
	  if (res->wd == -1 && errno == ENOENT)
	    die(_("directory %s for resolv-file is missing, cannot poll"), res->name, EC_MISC);
	  
	  if (res->wd == -1)
	    die(_("failed to create inotify for %s: %s"), res->name, EC_MISC);
	}
    }
}

int inotify_check(time_t now)
{
  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;

#ifdef HAVE_DHCP
	  if (daemon->dhcp || daemon->doing_dhcp6)
	    check_for_dhcp_inotify(in, now);
#endif
	}
    }
  return hit;
}

#ifdef HAVE_DHCP 
/* initialisation for dhcp-hostdir. Set inotify watch for each directory, and read pre-existing files */
void set_dhcp_inotify(void)
{
  struct hostsfile *ah;

  for (ah = daemon->inotify_hosts; ah; ah = ah->next)
    {
       DIR *dir_stream = NULL;
       struct dirent *ent;
       struct stat buf;

       if (stat(ah->fname, &buf) == -1 || !(S_ISDIR(buf.st_mode)))
	 {
	   my_syslog(LOG_ERR, _("bad directory in dhcp-hostsdir %s"), ah->fname);
	   continue;
	 }

       if (!(ah->flags & AH_WD_DONE))
	 {
	   ah->wd = inotify_add_watch(daemon->inotifyfd, ah->fname, IN_CLOSE_WRITE | IN_MOVED_TO);
	   ah->flags |= AH_WD_DONE;
	 }
       /* Read contents of dir _after_ calling add_watch, in the ho[e of avoiding
	  a race which misses files being added as we start */
       if (ah->wd == -1 || !(dir_stream = opendir(ah->fname)))
	 {
	   my_syslog(LOG_ERR, _("failed to create inotify for %s"), ah->fname);
	   continue;
	 }

       while ((ent = readdir(dir_stream)))
	 {
	   size_t lendir = strlen(ah->fname);
	   size_t lenfile = strlen(ent->d_name);
	   char *path;
	   
	   /* ignore emacs backups and dotfiles */
	   if (lenfile == 0 || 
	       ent->d_name[lenfile - 1] == '~' ||
	       (ent->d_name[0] == '#' && ent->d_name[lenfile - 1] == '#') ||
	       ent->d_name[0] == '.')
	     continue;
	   
	   if ((path = whine_malloc(lendir + lenfile + 2)))
	     {
	       strcpy(path, ah->fname);
	       strcat(path, "/");
	       strcat(path, ent->d_name);
	       
	       /* ignore non-regular files */
	       if (stat(path, &buf) != -1 && S_ISREG(buf.st_mode))
		 option_read_hostsfile(path);
	       
	       free(path);
	     }
	 }
    }
}

static void check_for_dhcp_inotify(struct inotify_event *in, time_t now)
{
  struct hostsfile *ah;

  /* ignore emacs backups and dotfiles */
  if (in->len == 0 || 
      in->name[in->len - 1] == '~' ||
      (in->name[0] == '#' && in->name[in->len - 1] == '#') ||
      in->name[0] == '.')
    return;

  for (ah = daemon->inotify_hosts; ah; ah = ah->next)
    if (ah->wd == in->wd)
      {
	size_t lendir = strlen(ah->fname);
	char *path;
	   
	if ((path = whine_malloc(lendir + in->len + 2)))
	  {
	    strcpy(path, ah->fname);
	    strcat(path, "/");
	    strcat(path, in->name);
	    
	    if (option_read_hostsfile(path))
	      {
		/* Propogate the consequences of loading a new dhcp-host */
		dhcp_update_configs(daemon->dhcp_conf);
		lease_update_from_configs(); 
		lease_update_file(now); 
		lease_update_dns(1);
	      }
	    
	    free(path);
	  }
	
	return;
      }
}

#endif /* DHCP */

#endif  /* LINUX_NETWORK */