Added option to re-open files to poller.

Some times a sysfs/debug fs will only generate a value on open. Subsequent seek/read will not vield any new values. This patch adds the option to reopen all files on each read.

wa/instruments/poller/__init__.py

@@ -59,6 +59,12 @@ class FilePoller(Instrument):
                   Whether or not the poller will be run as root. This should be
                   used when the file you need to poll can only be accessed by root.
                   """),
+        Parameter('reopen', kind=bool, default=False,
+                  description="""
+                  When enabled files will be re-opened with each read. This is
+                  useful for some sysfs/debugfs entries that only generate a
+                  value when opened.
+                  """),
     ]
 
     def validate(self):
@@ -91,13 +97,17 @@ class FilePoller(Instrument):
         if self.align_with_ftrace:
             marker_option = '-m'
             signal.connect(self._adjust_timestamps, signal.AFTER_JOB_OUTPUT_PROCESSED)
-        self.command = '{} -t {} {} -l {} {} > {} 2>{}'.format(target_poller,
+        reopen_option = ''
-                                                               self.sample_interval * 1000,
+        if self.reopen:
-                                                               marker_option,
+            reopen_option = '-r'
-                                                               ','.join(self.labels),
+        self.command = '{} {} -t {} {} -l {} {} > {} 2>{}'.format(target_poller,
-                                                               ' '.join(self.files),
+                                                                  reopen_option,
-                                                               self.target_output_path,
+                                                                  self.sample_interval * 1000,
-                                                               self.target_log_path)
+                                                                  marker_option,
+                                                                  ','.join(self.labels),
+                                                                  ' '.join(self.files),
+                                                                  self.target_output_path,
+                                                                  self.target_log_path)
 
     def start(self, context):
         self.target.kick_off(self.command, as_root=self.as_root)

wa/instruments/poller/poller.c

@@ -77,9 +77,10 @@ int main(int argc, char ** argv) {
     char *labels;
     int labelCount = 0;
     int should_write_marker = 0;
+    int reopen_files = 0;
     int ret;
 
-    static char usage[] = "usage: %s [-h] [-m] [-t INTERVAL] FILE [FILE ...]\n"
+    static char usage[] = "usage: %s [-h] [-m] [-r] [-t INTERVAL] FILE [FILE ...]\n"
                           "polls FILE(s) every INTERVAL microseconds and outputs\n"
                           "the results in CSV format including a timestamp to STDOUT\n"
                           "\n"
@@ -87,6 +88,7 @@ int main(int argc, char ** argv) {
                           "    -m     Insert a marker into ftrace at the time of the first\n"
                           "           sample. This marker may be used to align the timestamps\n"
                           "           produced by the poller with those of ftrace events.\n"
+                          "    -r     Reopen files on each read (needed for some sysfs/debugfs files)\n"
                           "    -t     The polling sample interval in microseconds\n"
                           "           Defaults to 1000000 (1 second)\n"
                           "    -l     Comma separated list of labels to use in the CSV\n"
@@ -94,7 +96,7 @@ int main(int argc, char ** argv) {
 
 
     //Handling command line arguments
-    while ((c = getopt(argc, argv, "hmt:l:")) != -1)
+    while ((c = getopt(argc, argv, "hmrt:l:")) != -1)
     {
         switch(c) {
             case 'h':
@@ -104,7 +106,10 @@ int main(int argc, char ** argv) {
                 break;
             case 'm':
                 should_write_marker = 1;
-		break;
+                break;
+            case 'r':
+                reopen_files = 1;
+                break;
             case 't':
                 interval = (useconds_t)atoi(optarg);
                 break;
@@ -184,7 +189,20 @@ int main(int argc, char ** argv) {
         time_float += ((double)current_time.tv_nsec)/1000/1000/1000;
         printf("%f", time_float);
         for (i = 0; i < num_files; i++) {
-            lseek(files_to_poll[i].fd, 0, SEEK_SET);
+            if (reopen_files) {
+                // Close and reopen the file to get fresh data
+                close(files_to_poll[i].fd);
+                files_to_poll[i].fd = open(files_to_poll[i].path, O_RDONLY);
+                if (files_to_poll[i].fd == -1) {
+                    fprintf(stderr, "WARNING: Could not reopen \"%s\", got: %s\n",
+                            files_to_poll[i].path, strerror(errno));
+                    printf(",");
+                    continue;
+                }
+            } else {
+                lseek(files_to_poll[i].fd, 0, SEEK_SET);
+            }
+
             bytes_read = read(files_to_poll[i].fd, buf, 1024);
 
             if (bytes_read < 0) {