dm: add statistics support

Support the collection of I/O statistics on user-defined regions of
a DM device.  If no regions are defined no statistics are collected so
there isn't any performance impact.  Only bio-based DM devices are
currently supported.

Each user-defined region specifies a starting sector, length and step.
Individual statistics will be collected for each step-sized area within
the range specified.

The I/O statistics counters for each step-sized area of a region are
in the same format as /sys/block/*/stat or /proc/diskstats but extra
counters (12 and 13) are provided: total time spent reading and
writing in milliseconds.  All these counters may be accessed by sending
the @stats_print message to the appropriate DM device via dmsetup.

The creation of DM statistics will allocate memory via kmalloc or
fallback to using vmalloc space.  At most, 1/4 of the overall system
memory may be allocated by DM statistics.  The admin can see how much
memory is used by reading
/sys/module/dm_mod/parameters/stats_current_allocated_bytes

See Documentation/device-mapper/statistics.txt for more details.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index e9c0de75010e..afe08146f73e 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1455,20 +1455,26 @@ static int table_status(struct dm_ioctl *param, size_t param_size)
         return 0;
 }
 
-static bool buffer_test_overflow(char *result, unsigned maxlen)
-{
-        return !maxlen || strlen(result) + 1 >= maxlen;
-}
-
 /*
- * Process device-mapper dependent messages.
+ * Process device-mapper dependent messages.  Messages prefixed with '@'
+ * are processed by the DM core.  All others are delivered to the target.
  * Returns a number <= 1 if message was processed by device mapper.
  * Returns 2 if message should be delivered to the target.
  */
 static int message_for_md(struct mapped_device *md, unsigned argc, char **argv,
                           char *result, unsigned maxlen)
 {
-        return 2;
+        int r;
+
+        if (**argv != '@')
+                return 2; /* no '@' prefix, deliver to target */
+
+        r = dm_stats_message(md, argc, argv, result, maxlen);
+        if (r < 2)
+                return r;
+
+        DMERR("Unsupported message sent to DM core: %s", argv[0]);
+        return -EINVAL;
 }
 
 /*
@@ -1542,7 +1548,7 @@ static int target_message(struct dm_ioctl *param, size_t param_size)
 
         if (r == 1) {
                 param->flags |= DM_DATA_OUT_FLAG;
-                if (buffer_test_overflow(result, maxlen))
+                if (dm_message_test_buffer_overflow(result, maxlen))
                         param->flags |= DM_BUFFER_FULL_FLAG;
                 else
                         param->data_size = param->data_start + strlen(result) + 1;