-EXPERIMENTAL-
As of now when primary SB fails we won't self heal and would fail mount,
this is an experimental patch which thinks why not go and read backup
copy.

Signed-off-by: Anand Jain <anand.j...@oracle.com>
---
 fs/btrfs/disk-io.c |  8 +++++++-
 fs/btrfs/volumes.c | 10 +++++++---
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 9b20c1f3563b..a791b8dfe8a8 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3190,7 +3190,7 @@ struct buffer_head *btrfs_read_dev_super(struct 
block_device *bdev)
         * So, we need to add a special mount option to scan for
         * later supers, using BTRFS_SUPER_MIRROR_MAX instead
         */
-       for (i = 0; i < 1; i++) {
+       for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
                ret = btrfs_read_dev_one_super(bdev, i, &bh);
                if (ret)
                        continue;
@@ -4015,11 +4015,17 @@ static int btrfs_check_super_valid(struct btrfs_fs_info 
*fs_info)
                ret = -EINVAL;
        }
 
+#if 0
+       /*
+        * Need a way to check for any copy of SB, as its not a
+        * strong check, just ignore this for now.
+        */
        if (btrfs_super_bytenr(sb) != BTRFS_SUPER_INFO_OFFSET) {
                btrfs_err(fs_info, "super offset mismatch %llu != %u",
                          btrfs_super_bytenr(sb), BTRFS_SUPER_INFO_OFFSET);
                ret = -EINVAL;
        }
+#endif
 
        /*
         * Obvious sys_chunk_array corruptions, it must hold at least one key
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 9fa2539a8493..f368db94d62b 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1369,7 +1369,7 @@ int btrfs_scan_one_device(const char *path, fmode_t 
flags, void *holder,
 {
        struct btrfs_super_block *disk_super;
        struct block_device *bdev;
-       struct page *page;
+       struct buffer_head *sb_bh;
        int ret = -EINVAL;
        u64 devid;
        u64 transid;
@@ -1392,8 +1392,12 @@ int btrfs_scan_one_device(const char *path, fmode_t 
flags, void *holder,
                goto error;
        }
 
-       if (btrfs_read_disk_super(bdev, bytenr, &page, &disk_super))
+       sb_bh = btrfs_read_dev_super(bdev);
+       if (IS_ERR(sb_bh)) {
+               ret = PTR_ERR(sb_bh);
                goto error_bdev_put;
+       }
+       disk_super = (struct btrfs_super_block *) sb_bh->b_data;
 
        devid = btrfs_stack_device_id(&disk_super->dev_item);
        transid = btrfs_super_generation(disk_super);
@@ -1413,7 +1417,7 @@ int btrfs_scan_one_device(const char *path, fmode_t 
flags, void *holder,
        if (!ret && fs_devices_ret)
                (*fs_devices_ret)->total_devices = total_devices;
 
-       btrfs_release_disk_super(page);
+       brelse(sb_bh);
 
 error_bdev_put:
        blkdev_put(bdev, flags);
-- 
2.7.0

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