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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>
This commit is contained in:
Nikanth Karthikesan 2009-03-24 12:29:54 +01:00 committed by Jens Axboe
parent 05378940ca
commit 68db1961bb
1 changed files with 30 additions and 2 deletions
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32
drivers/block/loop.c
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@ -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);