block: add a bdev_write_cache helper

Add a helper to check the write cache flag based on the block_device
instead of having to poke into the block layer internal request_queue.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: David Sterba <dsterba@suse.com> [btrfs]
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20220415045258.199825-13-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/rnbd/rnbd-srv.c

@@ -558,7 +558,7 @@ static void rnbd_srv_fill_msg_open_rsp(struct rnbd_msg_open_rsp *rsp,
 	rsp->secure_discard =
 		cpu_to_le16(rnbd_dev_get_secure_discard(rnbd_dev));
 	rsp->cache_policy = 0;
-	if (test_bit(QUEUE_FLAG_WC, &q->queue_flags))
+	if (bdev_write_cache(rnbd_dev->bdev))
 		rsp->cache_policy |= RNBD_WRITEBACK;
 	if (blk_queue_fua(q))
 		rsp->cache_policy |= RNBD_FUA;

drivers/block/xen-blkback/xenbus.c

@@ -517,7 +517,7 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
 		vbd->type |= VDISK_REMOVABLE;
 
 	q = bdev_get_queue(bdev);
-	if (q && test_bit(QUEUE_FLAG_WC, &q->queue_flags))
+	if (bdev_write_cache(bdev))
 		vbd->flush_support = true;
 
 	if (q && blk_queue_secure_erase(q))

drivers/target/target_core_iblock.c

@@ -737,7 +737,7 @@ iblock_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
 		if (test_bit(QUEUE_FLAG_FUA, &q->queue_flags)) {
 			if (cmd->se_cmd_flags & SCF_FUA)
 				opf |= REQ_FUA;
-			else if (!test_bit(QUEUE_FLAG_WC, &q->queue_flags))
+			else if (!bdev_write_cache(ib_dev->ibd_bd))
 				opf |= REQ_FUA;
 		}
 	} else {
@@ -886,11 +886,7 @@ iblock_parse_cdb(struct se_cmd *cmd)
 
 static bool iblock_get_write_cache(struct se_device *dev)
 {
-	struct iblock_dev *ib_dev = IBLOCK_DEV(dev);
-	struct block_device *bd = ib_dev->ibd_bd;
-	struct request_queue *q = bdev_get_queue(bd);
-
-	return test_bit(QUEUE_FLAG_WC, &q->queue_flags);
+	return bdev_write_cache(IBLOCK_DEV(dev)->ibd_bd);
 }
 
 static const struct target_backend_ops iblock_ops = {

fs/btrfs/disk-io.c

@@ -4249,8 +4249,7 @@ static void write_dev_flush(struct btrfs_device *device)
 	 * of simplicity, since this is a debug tool and not meant for use in
 	 * non-debug builds.
 	 */
-	struct request_queue *q = bdev_get_queue(device->bdev);
-	if (!test_bit(QUEUE_FLAG_WC, &q->queue_flags))
+	if (!bdev_write_cache(device->bdev))
 		return;
 #endif
 

include/linux/blkdev.h

@@ -1331,6 +1331,11 @@ static inline bool bdev_nonrot(struct block_device *bdev)
 	return blk_queue_nonrot(bdev_get_queue(bdev));
 }
 
+static inline bool bdev_write_cache(struct block_device *bdev)
+{
+	return test_bit(QUEUE_FLAG_WC, &bdev_get_queue(bdev)->queue_flags);
+}
+
 static inline enum blk_zoned_model bdev_zoned_model(struct block_device *bdev)
 {
 	struct request_queue *q = bdev_get_queue(bdev);