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>

8 files changed, 40 insertions, 28 deletions

diff --git a/block/genhd.c b/block/genhd.c
index f1543a45e73b..0711a800d0d4 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1337,14 +1337,14 @@ static int diskstats_show(struct seq_file *seqf, void *v)
                            "%u %lu %lu %lu %u %u %u %u\n",
                            MAJOR(part_devt(hd)), MINOR(part_devt(hd)),
                            disk_name(gp, hd->partno, buf),
-                           part_stat_read(hd, ios[READ]),
-                           part_stat_read(hd, merges[READ]),
-                           part_stat_read(hd, sectors[READ]),
-                           jiffies_to_msecs(part_stat_read(hd, ticks[READ])),
-                           part_stat_read(hd, ios[WRITE]),
-                           part_stat_read(hd, merges[WRITE]),
-                           part_stat_read(hd, sectors[WRITE]),
-                           jiffies_to_msecs(part_stat_read(hd, ticks[WRITE])),
+                           part_stat_read(hd, ios[STAT_READ]),
+                           part_stat_read(hd, merges[STAT_READ]),
+                           part_stat_read(hd, sectors[STAT_READ]),
+                           jiffies_to_msecs(part_stat_read(hd, ticks[STAT_READ])),
+                           part_stat_read(hd, ios[STAT_WRITE]),
+                           part_stat_read(hd, merges[STAT_WRITE]),
+                           part_stat_read(hd, sectors[STAT_WRITE]),
+                           jiffies_to_msecs(part_stat_read(hd, ticks[STAT_WRITE])),
                            inflight[0],
                            jiffies_to_msecs(part_stat_read(hd, io_ticks)),
                            jiffies_to_msecs(part_stat_read(hd, time_in_queue))
diff --git a/block/partition-generic.c b/block/partition-generic.c
index 3dcfd4ec0e11..0ddb06722162 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -132,14 +132,14 @@ ssize_t part_stat_show(struct device *dev,
                 "%8lu %8lu %8llu %8u "
                 "%8u %8u %8u"
                 "\n",
-                part_stat_read(p, ios[READ]),
-                part_stat_read(p, merges[READ]),
-                (unsigned long long)part_stat_read(p, sectors[READ]),
-                jiffies_to_msecs(part_stat_read(p, ticks[READ])),
-                part_stat_read(p, ios[WRITE]),
-                part_stat_read(p, merges[WRITE]),
-                (unsigned long long)part_stat_read(p, sectors[WRITE]),
-                jiffies_to_msecs(part_stat_read(p, ticks[WRITE])),
+                part_stat_read(p, ios[STAT_READ]),
+                part_stat_read(p, merges[STAT_READ]),
+                (unsigned long long)part_stat_read(p, sectors[STAT_READ]),
+                jiffies_to_msecs(part_stat_read(p, ticks[STAT_READ])),
+                part_stat_read(p, ios[STAT_WRITE]),
+                part_stat_read(p, merges[STAT_WRITE]),
+                (unsigned long long)part_stat_read(p, sectors[STAT_WRITE]),
+                jiffies_to_msecs(part_stat_read(p, ticks[STAT_WRITE])),
                 inflight[0],
                 jiffies_to_msecs(part_stat_read(p, io_ticks)),
                 jiffies_to_msecs(part_stat_read(p, time_in_queue)));
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index ba2396a7bd04..4b8aef989552 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3514,7 +3514,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
         sbi->s_sb_block = sb_block;
         if (sb->s_bdev->bd_part)
                 sbi->s_sectors_written_start =
-                        part_stat_read(sb->s_bdev->bd_part, sectors[1]);
+                        part_stat_read(sb->s_bdev->bd_part, sectors[STAT_WRITE]);
 
         /* Cleanup superblock name */
         strreplace(sb->s_id, '/', '!');
@@ -4824,7 +4824,8 @@ static int ext4_commit_super(struct super_block *sb, int sync)
         if (sb->s_bdev->bd_part)
                 es->s_kbytes_written =
                         cpu_to_le64(EXT4_SB(sb)->s_kbytes_written +
-                            ((part_stat_read(sb->s_bdev->bd_part, sectors[1]) -
+                            ((part_stat_read(sb->s_bdev->bd_part,
+                                             sectors[STAT_WRITE]) -
                               EXT4_SB(sb)->s_sectors_written_start) >> 1));
         else
                 es->s_kbytes_written =
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index f34da0bb8f17..2be9ad790017 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -56,7 +56,8 @@ static ssize_t session_write_kbytes_show(struct ext4_sb_info *sbi, char *buf)
         if (!sb->s_bdev->bd_part)
                 return snprintf(buf, PAGE_SIZE, "0\n");
         return snprintf(buf, PAGE_SIZE, "%lu\n",
-                        (part_stat_read(sb->s_bdev->bd_part, sectors[1]) -
+                        (part_stat_read(sb->s_bdev->bd_part,
+                                        sectors[STAT_WRITE]) -
                          sbi->s_sectors_written_start) >> 1);
 }
 
@@ -68,7 +69,8 @@ static ssize_t lifetime_write_kbytes_show(struct ext4_sb_info *sbi, char *buf)
                 return snprintf(buf, PAGE_SIZE, "0\n");
         return snprintf(buf, PAGE_SIZE, "%llu\n",
                         (unsigned long long)(sbi->s_kbytes_written +
-                        ((part_stat_read(sb->s_bdev->bd_part, sectors[1]) -
+                        ((part_stat_read(sb->s_bdev->bd_part,
+                                         sectors[STAT_WRITE]) -
                           EXT4_SB(sb)->s_sectors_written_start) >> 1)));
 }
 
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 4d8b1de83143..6799c3fc44e3 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1304,7 +1304,7 @@ static inline bool time_to_inject(struct f2fs_sb_info *sbi, int type)
  * and the return value is in kbytes. s is of struct f2fs_sb_info.
  */
 #define BD_PART_WRITTEN(s)                                               \
-(((u64)part_stat_read((s)->sb->s_bdev->bd_part, sectors[1]) -            \
+(((u64)part_stat_read((s)->sb->s_bdev->bd_part, sectors[STAT_WRITE]) -   \
                 (s)->sectors_written_start) >> 1)
 
 static inline void f2fs_update_time(struct f2fs_sb_info *sbi, int type)
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 3995e926ba3a..17bcff789c08 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2882,7 +2882,8 @@ try_onemore:
         /* For write statistics */
         if (sb->s_bdev->bd_part)
                 sbi->sectors_written_start =
-                        (u64)part_stat_read(sb->s_bdev->bd_part, sectors[1]);
+                        (u64)part_stat_read(sb->s_bdev->bd_part,
+                                            sectors[STAT_WRITE]);
 
         /* Read accumulated write IO statistics if exists */
         seg_i = CURSEG_I(sbi, CURSEG_HOT_NODE);
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index e13449a379a1..d2b44de56bc1 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -357,6 +357,13 @@ enum req_flag_bits {
 #define REQ_NOMERGE_FLAGS \
         (REQ_NOMERGE | REQ_PREFLUSH | REQ_FUA)
 
+enum stat_group {
+        STAT_READ,
+        STAT_WRITE,
+
+        NR_STAT_GROUPS
+};
+
 #define bio_op(bio) \
         ((bio)->bi_opf & REQ_OP_MASK)
 #define req_op(req) \
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);                   \