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>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 0f8e33f2bceabe87f8554ff297420ddd23acd46c..c7c739f420b5210bb07e4cef09b56961ec9961d2 100644 (file)
--- 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 bdfb479ea85955112305d0c30a17af9c7647daed..adeb31830b9cc1d49d145fdaa4f476c23dc81aa7 100644 (file)
--- 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);