[PATCH 2/5] btrfs: get bdev from latest_dev for dio bh_result

[David Sterba <dsterba@suse.com>]

To remove use of extent_map::bdev we need to find a replacement, and the
latest_bdev is the only one we can use here, because inode::i_bdev and
superblock::s_bdev are NULL.

The only thing that DIO code uses from the bdev is the blocksize to
perform alignment checks in do_blockdev_direct_IO, but we do them in
btrfs code before any call to DIO. We can't pass NULL because there are
dereferences of bdev in __blockdev_direct_IO, even though it's not going
to be used later.

So it's safe to pass any valid bdev that's used within the filesystem.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/inode.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 067cbd6e3923..8e085d21c3c5 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7603,6 +7603,8 @@ static int btrfs_get_blocks_direct_read(struct extent_map *em,
 					struct inode *inode,
 					u64 start, u64 len)
 {
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+
 	if (em->block_start == EXTENT_MAP_HOLE ||
 			test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
 		return -ENOENT;
@@ -7612,7 +7614,7 @@ static int btrfs_get_blocks_direct_read(struct extent_map *em,
 	bh_result->b_blocknr = (em->block_start + (start - em->start)) >>
 		inode->i_blkbits;
 	bh_result->b_size = len;
-	bh_result->b_bdev = em->bdev;
+	bh_result->b_bdev = fs_info->fs_devices->latest_bdev;
 	set_buffer_mapped(bh_result);
 
 	return 0;
@@ -7695,7 +7697,7 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,
 	bh_result->b_blocknr = (em->block_start + (start - em->start)) >>
 		inode->i_blkbits;
 	bh_result->b_size = len;
-	bh_result->b_bdev = em->bdev;
+	bh_result->b_bdev = fs_info->fs_devices->latest_bdev;
 	set_buffer_mapped(bh_result);
 
 	if (!test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
-- 
2.23.0