loop: support barrier writes

Honour barrier requests in the loop back block device driver.
In case of barrier bios, flush the backing file once before processing the
barrier and once after to guarantee ordering. In case of filesystems that
does not support fsync, barrier bios would be failed with -EOPNOTSUPP.

Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 30 insertions, 2 deletions

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index bf0345577672..9721d100caf1 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -474,10 +474,35 @@ static int do_bio_filebacked(struct loop_device *lo, struct bio *bio)
         int ret;
 
         pos = ((loff_t) bio->bi_sector << 9) + lo->lo_offset;
-        if (bio_rw(bio) == WRITE)
+
+        if (bio_rw(bio) == WRITE) {
+                int barrier = bio_barrier(bio);
+                struct file *file = lo->lo_backing_file;
+
+                if (barrier) {
+                        if (unlikely(!file->f_op->fsync)) {
+                                ret = -EOPNOTSUPP;
+                                goto out;
+                        }
+
+                        ret = vfs_fsync(file, file->f_path.dentry, 0);
+                        if (unlikely(ret)) {
+                                ret = -EIO;
+                                goto out;
+                        }
+                }
+
                 ret = lo_send(lo, bio, pos);
-        else
+
+                if (barrier && !ret) {
+                        ret = vfs_fsync(file, file->f_path.dentry, 0);
+                        if (unlikely(ret))
+                                ret = -EIO;
+                }
+        } else
                 ret = lo_receive(lo, bio, lo->lo_blocksize, pos);
+
+out:
         return ret;
 }
 
@@ -826,6 +851,9 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
         lo->lo_queue->queuedata = lo;
         lo->lo_queue->unplug_fn = loop_unplug;
 
+        if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync)
+                blk_queue_ordered(lo->lo_queue, QUEUE_ORDERED_DRAIN, NULL);
+
         set_capacity(lo->lo_disk, size);
         bd_set_size(bdev, size << 9);