md/raid10: change read_balance to return an rdev

It makes more sense to return an rdev than just an index as
read_balance() gets a reference to the rdev and so returning
the pointer make this more idiomatic.

This will be needed in a future patch when we might return
a 'replacement' rdev instead of the main rdev.

Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 9722065..70356c1 100644 (file)
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -590,7 +590,9 @@ static int raid10_mergeable_bvec(struct request_queue *q,
  * FIXME: possibly should rethink readbalancing and do it differently
  * depending on near_copies / far_copies geometry.
  */
-static int read_balance(struct r10conf *conf, struct r10bio *r10_bio, int *max_sectors)
+static struct md_rdev *read_balance(struct r10conf *conf,
+                                   struct r10bio *r10_bio,
+                                   int *max_sectors)
 {
        const sector_t this_sector = r10_bio->sector;
        int disk, slot;
@@ -703,11 +705,11 @@ retry:
                }
                r10_bio->read_slot = slot;
        } else
-               disk = -1;
+               rdev = NULL;
        rcu_read_unlock();
        *max_sectors = best_good_sectors;
 
-       return disk;
+       return rdev;
 }
 
 static int raid10_congested(void *data, int bits)
@@ -874,7 +876,6 @@ static void unfreeze_array(struct r10conf *conf)
 static void make_request(struct mddev *mddev, struct bio * bio)
 {
        struct r10conf *conf = mddev->private;
-       struct mirror_info *mirror;
        struct r10bio *r10_bio;
        struct bio *read_bio;
        int i;
@@ -973,17 +974,16 @@ static void make_request(struct mddev *mddev, struct bio * bio)
                /*
                 * read balancing logic:
                 */
-               int disk;
+               struct md_rdev *rdev;
                int slot;
 
 read_again:
-               disk = read_balance(conf, r10_bio, &max_sectors);
-               slot = r10_bio->read_slot;
-               if (disk < 0) {
+               rdev = read_balance(conf, r10_bio, &max_sectors);
+               if (!rdev) {
                        raid_end_bio_io(r10_bio);
                        return;
                }
-               mirror = conf->mirrors + disk;
+               slot = r10_bio->read_slot;
 
                read_bio = bio_clone_mddev(bio, GFP_NOIO, mddev);
                md_trim_bio(read_bio, r10_bio->sector - bio->bi_sector,
@@ -992,8 +992,8 @@ read_again:
                r10_bio->devs[slot].bio = read_bio;
 
                read_bio->bi_sector = r10_bio->devs[slot].addr +
-                       mirror->rdev->data_offset;
-               read_bio->bi_bdev = mirror->rdev->bdev;
+                       rdev->data_offset;
+               read_bio->bi_bdev = rdev->bdev;
                read_bio->bi_end_io = raid10_end_read_request;
                read_bio->bi_rw = READ | do_sync;
                read_bio->bi_private = r10_bio;
@@ -2116,8 +2116,8 @@ static void handle_read_error(struct mddev *mddev, struct r10bio *r10_bio)
        r10_bio->devs[slot].bio =
                mddev->ro ? IO_BLOCKED : NULL;
 read_more:
-       mirror = read_balance(conf, r10_bio, &max_sectors);
-       if (mirror == -1) {
+       rdev = read_balance(conf, r10_bio, &max_sectors);
+       if (rdev == NULL) {
                printk(KERN_ALERT "md/raid10:%s: %s: unrecoverable I/O"
                       " read error for block %llu\n",
                       mdname(mddev), b,
@@ -2131,7 +2131,6 @@ read_more:
        if (bio)
                bio_put(bio);
        slot = r10_bio->read_slot;
-       rdev = conf->mirrors[mirror].rdev;
        printk_ratelimited(
                KERN_ERR
                "md/raid10:%s: %s: redirecting"