zram: document failed_reads, failed_writes stats

Document `failed_reads' and `failed_writes' device attributes.
Remove info about `discard' - there is no such zram attr.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/ABI/testing/sysfs-block-zram

@@ -43,6 +43,21 @@ Description:
 		The invalid_io file is read-only and specifies the number of
 		non-page-size-aligned I/O requests issued to this device.
 
+What:		/sys/block/zram<id>/failed_reads
+Date:		February 2014
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The failed_reads file is read-only and specifies the number of
+		failed reads happened on this device.
+
+
+What:		/sys/block/zram<id>/failed_writes
+Date:		February 2014
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The failed_writes file is read-only and specifies the number of
+		failed writes happened on this device.
+
 What:		/sys/block/zram<id>/notify_free
 Date:		August 2010
 Contact:	Nitin Gupta <ngupta@vflare.org>
@@ -53,15 +68,6 @@ Description:
 		is freed. This statistic is applicable only when this disk is
 		being used as a swap disk.
 
-What:		/sys/block/zram<id>/discard
-Date:		August 2010
-Contact:	Nitin Gupta <ngupta@vflare.org>
-Description:
-		The discard file is read-only and specifies the number of
-		discard requests received by this device. These requests
-		provide information to block device regarding blocks which are
-		no longer used by filesystem.
-
 What:		/sys/block/zram<id>/zero_pages
 Date:		August 2010
 Contact:	Nitin Gupta <ngupta@vflare.org>

Documentation/blockdev/zram.txt

@@ -51,9 +51,10 @@ size of the disk when not in use so a huge zram is wasteful.
 		disksize
 		num_reads
 		num_writes
+		failed_reads
+		failed_writes
 		invalid_io
 		notify_free
-		discard
 		zero_pages
 		orig_data_size
 		compr_data_size