[PATCH 3/4] dm-latency: add sysfs interface

[Coly Li <colyli@gmail.com>]

From: Coly Li <bosong.ly@alibaba-inc.com>

This patch adds sysfs interface to display io latency statistic info.
3 files are used to export statistic info based on delay unit level,
- /sys/block/dm-X/dm/io_latency_us
- /sys/block/dm-X/dm/io_latency_ms
- /sys/block/dm-X/dm/io_latency_s

The statistic counter is increasing only, a user space application
should calculate "delta" value for a sampling interval.

Signed-off-by: Coly Li <bosong.ly@alibaba-inc.com>
Reviewed-by: Robin Dong <sanbai@alibaba-inc.com>
Reviewed-by: Tao Ma <boyu.mt@taobao.com>
---
  drivers/md/dm-sysfs.c |   70
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 70 insertions(+)

diff --git a/drivers/md/dm-sysfs.c b/drivers/md/dm-sysfs.c
index c62c5ab..eab2dde 100644
--- a/drivers/md/dm-sysfs.c
+++ b/drivers/md/dm-sysfs.c
@@ -6,6 +6,7 @@

  #include <linux/sysfs.h>
  #include <linux/dm-ioctl.h>
+#include <asm/atomic.h>
  #include "dm.h"

  struct dm_sysfs_attr {
@@ -64,14 +65,83 @@ static ssize_t dm_attr_suspended_show(struct
mapped_device *md, char *buf)
  	return strlen(buf);
  }

+static ssize_t dm_attr_io_latency_us_show(struct mapped_device *md,
char *buf)
+{
+	int slot_base = 0;
+	int i, nr, ptr;
+
+	for (ptr = 0, i = 0; i < DM_LATENCY_STATS_US_NR; i++) {
+		nr = sprintf(buf + ptr,
+			     "%d-%d(us):%d\n",
+			     slot_base,
+			     slot_base + DM_LATENCY_STATS_US_GRAINSIZE - 1,
+			     atomic_read(&md->latency_stats_us[i]));
+		if (nr < 0)
+			break;
+
+		slot_base += DM_LATENCY_STATS_US_GRAINSIZE;
+		ptr += nr;
+	}
+
+	return strlen(buf);
+}
+
+static ssize_t dm_attr_io_latency_ms_show(struct mapped_device *md,
char *buf)
+{
+	int slot_base = 0;
+	int i, nr, ptr;
+
+	for (ptr = 0, i = 0; i < DM_LATENCY_STATS_MS_NR; i++) {
+		nr = sprintf(buf + ptr,
+			     "%d-%d(ms):%d\n",
+			     slot_base,
+			     slot_base + DM_LATENCY_STATS_MS_GRAINSIZE - 1,
+			     atomic_read(&(md->latency_stats_ms[i])));
+		if (nr < 0)
+			break;
+
+		slot_base += DM_LATENCY_STATS_MS_GRAINSIZE;
+		ptr += nr;
+	}
+
+	return strlen(buf);
+}
+
+static ssize_t dm_attr_io_latency_s_show(struct mapped_device *md, char
*buf)
+{
+	int slot_base = 0;
+	int i, nr , ptr;
+
+	for(ptr = 0, i = 0; i < DM_LATENCY_STATS_S_NR; i++) {
+		nr = sprintf(buf + ptr,
+			      "%d-%d(s):%d\n",
+			      slot_base,
+			      slot_base + DM_LATENCY_STATS_S_GRAINSIZE - 1,
+			      atomic_read(&(md->latency_stats_s[i])));
+		if (nr < 0)
+			break;
+
+		slot_base += DM_LATENCY_STATS_S_GRAINSIZE;
+		ptr += nr;
+	}
+
+	return strlen(buf);
+}
+
  static DM_ATTR_RO(name);
  static DM_ATTR_RO(uuid);
  static DM_ATTR_RO(suspended);
+static DM_ATTR_RO(io_latency_us);
+static DM_ATTR_RO(io_latency_ms);
+static DM_ATTR_RO(io_latency_s);

  static struct attribute *dm_attrs[] = {
  	&dm_attr_name.attr,
  	&dm_attr_uuid.attr,
  	&dm_attr_suspended.attr,
+	&dm_attr_io_latency_us.attr,
+	&dm_attr_io_latency_ms.attr,
+	&dm_attr_io_latency_s.attr,
  	NULL,
  };