[PATCH 5/6] zram: export new 'io_stat' sysfs attrs

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

Per-device `zram<id>/io_stat' file provides accumulated I/O statistics
of particular zram device in a format similar to block layer statistics.
The file consists of a single line and represents the following stats
(separated by whitespace):
	failed_reads
	failed_writes
	invalid_io
	notify_free

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 Documentation/ABI/testing/sysfs-block-zram |  9 +++++++++
 Documentation/blockdev/zram.txt            | 12 ++++++++++++
 drivers/block/zram/zram_drv.c              | 20 ++++++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index 91ad707..a7f622f 100644
--- a/Documentation/ABI/testing/sysfs-block-zram
+++ b/Documentation/ABI/testing/sysfs-block-zram
@@ -149,3 +149,12 @@ Description:
 		The compact file is write-only and trigger compaction for
 		allocator zrm uses. The allocator moves some objects so that
 		it could free fragment space.
+
+What:		/sys/block/zram<id>/io_stat
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The io_stat file is read-only and accumulates device's I/O
+		statistics not accounted by block layer. For example,
+		failed_reads, failed_writes, etc. File format is similar to
+		block layer statistics file format.
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 149b49a..eb62792 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -153,6 +153,18 @@ File /sys/block/zram<id>/stat
 Represents block layer statistics. Read Documentation/block/stat.txt for
 details.
 
+
+File /sys/block/zram<id>/io_stat
+
+The stat file represents device's I/O statistics not accounted by block
+layer and, thus, not available in zram<id>/stat file. It consists of a
+single line of text and contains the following stats separated by
+whitespace:
+	failed_reads
+	failed_writes
+	invalid_io
+	notify_free
+
 9) Deactivate:
 	swapoff /dev/zram0
 	umount /dev/zram1
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 45319eb9..c02121f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -384,6 +384,25 @@ static ssize_t compact_store(struct device *dev,
 	return len;
 }
 
+static ssize_t io_stat_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	ssize_t ret;
+
+	down_read(&zram->init_lock);
+	ret = scnprintf(buf, PAGE_SIZE,
+			"%8llu %8llu %8llu %8llu\n",
+			(u64)atomic64_read(&zram->stats.failed_reads),
+			(u64)atomic64_read(&zram->stats.failed_writes),
+			(u64)atomic64_read(&zram->stats.invalid_io),
+			(u64)atomic64_read(&zram->stats.notify_free));
+	up_read(&zram->init_lock);
+
+	return ret;
+}
+
+static DEVICE_ATTR_RO(io_stat);
 ZRAM_ATTR_RO(num_reads);
 ZRAM_ATTR_RO(num_writes);
 ZRAM_ATTR_RO(failed_reads);
@@ -1085,6 +1104,7 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_mem_used_max.attr,
 	&dev_attr_max_comp_streams.attr,
 	&dev_attr_comp_algorithm.attr,
+	&dev_attr_io_stat.attr,
 	NULL,
 };
 
-- 
2.3.2.209.gd67f9d5