[PATCH v4 7/7] btrfs: check if the device is flush capable

[Anand Jain <anand.jain@oracle.com>]

The blkdev_issue_flush() will check if the write cache is enabled
before submitting the flush. This will add a code to fail fast if
its not.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
v2: This patch will now _not_ replace the below patch and this patch
  should be applied on top of it.
    [PATCH] btrfs: delete unused member nobarriers
  That's because, Q write cache flag is not static, so we can't save
  its state into nobarries.
  - commit log is updated.
v3: no change
v4: no change

 fs/btrfs/disk-io.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b6d047250ce2..bb5816c7f5c4 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3517,6 +3517,11 @@ static void btrfs_dev_issue_flush(struct work_struct *work)
  */
 static int write_dev_flush(struct btrfs_device *device, int wait)
 {
+	struct request_queue *q = bdev_get_queue(device->bdev);
+
+	if (!test_bit(QUEUE_FLAG_WC, &q->queue_flags))
+		return 0;
+
 	if (wait) {
 		int ret;
 
-- 
2.10.0