block: switch polling to be bio based

Replace the blk_poll interface that requires the caller to keep a queue
and cookie from the submissions with polling based on the bio.

Polling for the bio itself leads to a few advantages:

 - the cookie construction can made entirely private in blk-mq.c
 - the caller does not need to remember the request_queue and cookie
   separately and thus sidesteps their lifetime issues
 - keeping the device and the cookie inside the bio allows to trivially
   support polling BIOs remapping by stacking drivers
 - a lot of code to propagate the cookie back up the submission path can
   be removed entirely.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Mark Wunderlich <mark.wunderlich@intel.com>
Link: https://lore.kernel.org/r/20211012111226.760968-15-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4a9077c..04090ba 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8248,7 +8248,7 @@ static struct btrfs_dio_private *btrfs_create_dio_private(struct bio *dio_bio,
 	return dip;
 }
 
-static blk_qc_t btrfs_submit_direct(const struct iomap_iter *iter,
+static void btrfs_submit_direct(const struct iomap_iter *iter,
 		struct bio *dio_bio, loff_t file_offset)
 {
 	struct inode *inode = iter->inode;
@@ -8278,7 +8278,7 @@ static blk_qc_t btrfs_submit_direct(const struct iomap_iter *iter,
 		}
 		dio_bio->bi_status = BLK_STS_RESOURCE;
 		bio_endio(dio_bio);
-		return BLK_QC_T_NONE;
+		return;
 	}
 
 	if (!write) {
@@ -8372,15 +8372,13 @@ static blk_qc_t btrfs_submit_direct(const struct iomap_iter *iter,
 
 		free_extent_map(em);
 	} while (submit_len > 0);
-	return BLK_QC_T_NONE;
+	return;
 
 out_err_em:
 	free_extent_map(em);
 out_err:
 	dip->dio_bio->bi_status = status;
 	btrfs_dio_private_put(dip);
-
-	return BLK_QC_T_NONE;
 }
 
 const struct iomap_ops btrfs_dio_iomap_ops = {