[PATCH v3 1/2] DAX: enable iostat for read/write

[Toshi Kani]

DAX IO path does not support iostat, but its metadata IO path does.
Therefore, iostat shows metadata IO statistics only, which has been
confusing to users.

Add iostat support to the DAX read/write path.

Note, iostat still does not support the DAX mmap path as it allows
user applications to access directly.

Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
 fs/dax.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/dax.c b/fs/dax.c
index 014defd..2646969 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -265,9 +265,12 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
 	ssize_t retval = -EINVAL;
 	loff_t pos = iocb->ki_pos;
 	loff_t end = pos + iov_iter_count(iter);
+	struct gendisk *disk;
+	unsigned long start = 0;
 
 	memset(&bh, 0, sizeof(bh));
 	bh.b_bdev = inode->i_sb->s_bdev;
+	disk = bh.b_bdev->bd_disk;
 
 	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
 		inode_lock(inode);
@@ -276,8 +279,20 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
 	if (!(flags & DIO_SKIP_DIO_COUNT))
 		inode_dio_begin(inode);
 
+	if (blk_queue_io_stat(disk->queue)) {
+		int sec = iov_iter_count(iter) >> 9;
+
+		start = jiffies;
+		generic_start_io_acct(iov_iter_rw(iter),
+				      (!sec) ? 1 : sec, &disk->part0);
+	}
+
 	retval = dax_io(inode, iter, pos, end, get_block, &bh);
 
+	if (start)
+		generic_end_io_acct(iov_iter_rw(iter),
+				    &disk->part0, start);
+
 	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
 		inode_unlock(inode);