linux-kernel - Re: [PATCH] Block - Honour barrier requests in loop driver

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Date:	Wed, 18 Mar 2009 10:28:20 +0530
From:	Nikanth Karthikesan <knikanth@...e.de>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Gerd Hoffmann <kraxel@...hat.com>,
	Constantine Sapuntzakis <csapuntz@...il.com>,
	Miklos Szeredi <miklos@...redi.hu>, nikanth@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Block - Honour barrier requests in loop driver

On Wednesday 18 March 2009 00:39:05 Christoph Hellwig wrote:
> On Tue, Mar 17, 2009 at 05:39:49PM +0530, Nikanth Karthikesan wrote:
> > +			if (!file->f_op || !file->f_op->fsync) {
> > +				ret = -EOPNOTSUPP;
> > +				goto out;
> > +			}
>
> file->f_op is never zero, so you can remove the checks for that.
> Otherwise looks good.

Thanks for reviewing. I've removed that check.

Jens, Can you merge this?

Thanks
Nikanth

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@...e.de>

---

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index bf03455..cac7894 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;
 }
 
@@ -825,6 +850,10 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 	blk_queue_make_request(lo->lo_queue, loop_make_request);
 	lo->lo_queue->queuedata = lo;
 	lo->lo_queue->unplug_fn = loop_unplug;
+	if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op &&
+						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);

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