Hi!

quoted

+* COUNTER_ENABLE_EVENTS_IOCTL:
+  Enables monitoring the events specified by the Counter watches that
+  were queued by ``COUNTER_ADD_WATCH_IOCTL``. If events are already
+  enabled, the new set of watches replaces the old one. Calling this
+  ioctl also has the effect of clearing the queue of watches added by
+  ``COUNTER_ADD_WATCH_IOCTL``.
+
+* COUNTER_DISABLE_EVENTS_IOCTL:
+  Stops monitoring the previously enabled events.

Is there a way to remove a watch? 

Is there a way to eat all kernel memory and crash the system by adding
too many watches?

quoted

+For example, the following userspace code opens ``/dev/counter0``,
+configures the ``COUNTER_EVENT_INDEX`` event channel 0 to gather Count 0
+and Count 1, and prints out the data as it becomes available on the
+character device node::
+

Consider adding an example program under tools/

quoted

+        #include <fcntl.h>
+        #include <linux/counter.h>
+        #include <stdio.h>
+        #include <string.h>
+        #include <sys/ioctl.h>
+        #include <unistd.h>
+
+        struct counter_watch watches[2] = {
+                {
+                        .component.type = COUNTER_COMPONENT_COUNT,
+                        .component.scope = COUNTER_SCOPE_COUNT,
+                        .component.parent = 0,

Good to add comments on what these elements actually are?

quoted

+                fd = open("/dev/counter0", O_RDWR);
+
+                ioctl(fd, COUNTER_ADD_WATCH_IOCTL, watches);
+                ioctl(fd, COUNTER_ADD_WATCH_IOCTL, watches + 1);
+                ioctl(fd, COUNTER_ENABLE_EVENTS_IOCTL);

quoted

+                for (;;) {
+                        read(fd, event_data, sizeof(event_data));

If this goes to tools it really should have error handling and
handling of short read.

Best regards,
							Pavel

-- 
http://www.livejournal.com/~pavelmachek