Btrfs: add btrfs_read_dev_one_super() to read one specific SB

This uses a chunk of code from btrfs_read_dev_super() and creates
a function called btrfs_read_dev_one_super() so that next patch
can use it for scratch superblock.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
[renamed bufhead to bh]
Signed-off-by: David Sterba <dsterba@suse.com>

2 files changed, 35 insertions, 20 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 0f8e33f2bcea..c7c739f420b5 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3188,6 +3188,37 @@ static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
         put_bh(bh);
 }
 
+int btrfs_read_dev_one_super(struct block_device *bdev, int copy_num,
+                        struct buffer_head **bh_ret)
+{
+        struct buffer_head *bh;
+        struct btrfs_super_block *super;
+        u64 bytenr;
+
+        bytenr = btrfs_sb_offset(copy_num);
+        if (bytenr + BTRFS_SUPER_INFO_SIZE >= i_size_read(bdev->bd_inode))
+                return -EINVAL;
+
+        bh = __bread(bdev, bytenr / 4096, BTRFS_SUPER_INFO_SIZE);
+        /*
+         * If we fail to read from the underlying devices, as of now
+         * the best option we have is to mark it EIO.
+         */
+        if (!bh)
+                return -EIO;
+
+        super = (struct btrfs_super_block *)bh->b_data;
+        if (btrfs_super_bytenr(super) != bytenr ||
+                    btrfs_super_magic(super) != BTRFS_MAGIC) {
+                brelse(bh);
+                return -EINVAL;
+        }
+
+        *bh_ret = bh;
+        return 0;
+}
+
+
 struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
 {
         struct buffer_head *bh;
@@ -3195,7 +3226,6 @@ struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
         struct btrfs_super_block *super;
         int i;
         u64 transid = 0;
-        u64 bytenr;
         int ret = -EINVAL;
 
         /* we would like to check all the supers, but that would make
@@ -3204,28 +3234,11 @@ struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
          * later supers, using BTRFS_SUPER_MIRROR_MAX instead
          */
         for (i = 0; i < 1; i++) {
-                bytenr = btrfs_sb_offset(i);
-                if (bytenr + BTRFS_SUPER_INFO_SIZE >=
-                                        i_size_read(bdev->bd_inode))
-                        break;
-                bh = __bread(bdev, bytenr / 4096,
-                                        BTRFS_SUPER_INFO_SIZE);
-                /*
-                 * If we fail to read from the underlying devices, as of now
-                 * the best option we have is to mark it EIO.
-                 */
-                if (!bh) {
-                        ret = -EIO;
+                ret = btrfs_read_dev_one_super(bdev, i, &bh);
+                if (ret)
                         continue;
-                }
 
                 super = (struct btrfs_super_block *)bh->b_data;
-                if (btrfs_super_bytenr(super) != bytenr ||
-                    btrfs_super_magic(super) != BTRFS_MAGIC) {
-                        brelse(bh);
-                        ret = -EINVAL;
-                        continue;
-                }
 
                 if (!latest || btrfs_super_generation(super) > transid) {
                         brelse(latest);
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index bdfb479ea859..adeb31830b9c 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -60,6 +60,8 @@ void close_ctree(struct btrfs_root *root);
 int write_ctree_super(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root, int max_mirrors);
 struct buffer_head *btrfs_read_dev_super(struct block_device *bdev);
+int btrfs_read_dev_one_super(struct block_device *bdev, int copy_num,
+                        struct buffer_head **bh_ret);
 int btrfs_commit_super(struct btrfs_root *root);
 struct extent_buffer *btrfs_find_tree_block(struct btrfs_fs_info *fs_info,
                                             u64 bytenr);