block: Define and use STAT_READ and STAT_WRITE

Add defines for STAT_READ and STAT_WRITE for indexing the partition
stat entries. This clarifies some fs/ code which has hardcoded 1 for
STAT_WRITE and will make it easier to extend the stats with additional
fields.

tj: Refreshed on top of v4.17.

Signed-off-by: Michael Callahan <michaelcallahan@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 7 insertions, 6 deletions

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 19f36fa10995..a75445446974 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -16,6 +16,7 @@
 #include <linux/slab.h>
 #include <linux/percpu-refcount.h>
 #include <linux/uuid.h>
+#include <linux/blk_types.h>
 
 #ifdef CONFIG_BLOCK
 
@@ -82,10 +83,10 @@ struct partition {
 } __attribute__((packed));
 
 struct disk_stats {
-        unsigned long sectors[2];       /* READs and WRITEs */
-        unsigned long ios[2];
-        unsigned long merges[2];
-        unsigned long ticks[2];
+        unsigned long sectors[NR_STAT_GROUPS];
+        unsigned long ios[NR_STAT_GROUPS];
+        unsigned long merges[NR_STAT_GROUPS];
+        unsigned long ticks[NR_STAT_GROUPS];
         unsigned long io_ticks;
         unsigned long time_in_queue;
 };
@@ -354,8 +355,8 @@ static inline void free_part_stats(struct hd_struct *part)
 #endif /* CONFIG_SMP */
 
 #define part_stat_read_accum(part, field)                               \
-        (part_stat_read(part, field[0]) +                               \
-         part_stat_read(part, field[1]))
+        (part_stat_read(part, field[STAT_READ]) +                       \
+         part_stat_read(part, field[STAT_WRITE]))
 
 #define part_stat_add(cpu, part, field, addnd)  do {                    \
         __part_stat_add((cpu), (part), field, addnd);                   \