ENH(+possibly BF): for FilterPoll rely not only on mtime but also ino and size to assess if file was modified

mtime alone is a poor measure here as many of our tests shown -- on older Pythons and some file systems
mtime might be reported only with precision up to a second.  If file gets rotated fast, or there are new
modifications within the same second, fail2ban might miss them with Polling backend if judging only by
mtime.  With this modification we will track also inode and size which are all indicative of a file
change.

server/filterpoll.py

@@ -57,7 +57,7 @@ class FilterPoll(FileFilter):
 		FileFilter.__init__(self, jail)
 		self.__modified = False
 		## The time of the last modification of the file.
-		self.__lastModTime = dict()
+		self.__prevStats = dict()
 		self.__file404Cnt = dict()
 		logSys.debug("Created FilterPoll")
 
@@ -67,7 +67,7 @@ class FilterPoll(FileFilter):
 	# @param path log file path
 
 	def _addLogPath(self, path):
-		self.__lastModTime[path] = 0
+		self.__prevStats[path] = (0, None, None)	 # mtime, ino, size
 		self.__file404Cnt[path] = 0
 
 	##
@@ -76,7 +76,7 @@ class FilterPoll(FileFilter):
 	# @param path the log file to delete
 
 	def _delLogPath(self, path):
-		del self.__lastModTime[path]
+		del self.__prevStats[path]
 		del self.__file404Cnt[path]
 
 	##
@@ -126,18 +126,20 @@ class FilterPoll(FileFilter):
 	def isModified(self, filename):
 		try:
 			logStats = os.stat(filename)
+			stats = logStats.st_mtime, logStats.st_ino, logStats.st_size
+			pstats = self.__prevStats[filename]
 			self.__file404Cnt[filename] = 0
 			if logSys.getEffectiveLevel() <= 7:
 				# we do not want to waste time on strftime etc if not necessary
-				dt = logStats.st_mtime - self.__lastModTime[filename]
+				dt = logStats.st_mtime - pstats[0]
-				logSys.log(7, "Checking %s for being modified. Previous/current mtimes: %s / %s. dt: %s",
+				logSys.log(7, "Checking %s for being modified. Previous/current stats: %s / %s. dt: %s",
-				           filename, _ctime(self.__lastModTime[filename]), _ctime(logStats.st_mtime), dt)
+				           filename, pstats, stats, dt)
 				# os.system("stat %s | grep Modify" % filename)
-			if self.__lastModTime[filename] == logStats.st_mtime:
+			if pstats == stats:
 				return False
 			else:
-				logSys.debug(filename + " has been modified")
+				logSys.debug("%s has been modified", filename)
-				self.__lastModTime[filename] = logStats.st_mtime
+				self.__prevStats[filename] = stats
 				return True
 		except OSError, e:
 			logSys.error("Unable to get stat on %s because of: %s"