block: remove i_bdev

Switch the block device lookup interfaces to directly work with a dev_t
so that struct block_device references are only acquired by the
blkdev_get variants (and the blk-cgroup special case).  This means that
we now don't need an extra reference in the inode and can generally
simplify handling of struct block_device to keep the lookups contained
in the core block layer code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Coly Li <colyli@suse.de>		[bcache]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/target/target_core_file.c b/drivers/target/target_core_file.c
index 7143d03..b0cb5b9 100644
--- a/drivers/target/target_core_file.c
+++ b/drivers/target/target_core_file.c
@@ -133,10 +133,10 @@ static int fd_configure_device(struct se_device *dev)
 	 */
 	inode = file->f_mapping->host;
 	if (S_ISBLK(inode->i_mode)) {
-		struct request_queue *q = bdev_get_queue(inode->i_bdev);
+		struct request_queue *q = bdev_get_queue(I_BDEV(inode));
 		unsigned long long dev_size;
 
-		fd_dev->fd_block_size = bdev_logical_block_size(inode->i_bdev);
+		fd_dev->fd_block_size = bdev_logical_block_size(I_BDEV(inode));
 		/*
 		 * Determine the number of bytes from i_size_read() minus
 		 * one (1) logical sector from underlying struct block_device
@@ -559,7 +559,7 @@ fd_execute_unmap(struct se_cmd *cmd, sector_t lba, sector_t nolb)
 
 	if (S_ISBLK(inode->i_mode)) {
 		/* The backend is block device, use discard */
-		struct block_device *bdev = inode->i_bdev;
+		struct block_device *bdev = I_BDEV(inode);
 		struct se_device *dev = cmd->se_dev;
 
 		ret = blkdev_issue_discard(bdev,