nilfs2: replace barriers with explicit flush / FUA usage

Switch to the WRITE_FLUSH_FUA flag for log writes, remove the EOPNOTSUPP
detection for barriers and stop setting the barrier flag for discards.

tj: nilfs is now fixed to wait for discard completion.  Updated this
    patch accordingly and dropped warning about it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

fs/nilfs2/super.c

@@ -178,17 +178,9 @@ static int nilfs_sync_super(struct nilfs_sb_info *sbi, int flag)
 
  retry:
 	set_buffer_dirty(nilfs->ns_sbh[0]);
-
 	if (nilfs_test_opt(sbi, BARRIER)) {
 		err = __sync_dirty_buffer(nilfs->ns_sbh[0],
-					  WRITE_SYNC | WRITE_BARRIER);
-		if (err == -EOPNOTSUPP) {
-			nilfs_warning(sbi->s_super, __func__,
-				      "barrier-based sync failed. "
-				      "disabling barriers\n");
-			nilfs_clear_opt(sbi, BARRIER);
-			goto retry;
-		}
+					  WRITE_SYNC | WRITE_FLUSH_FUA);
 	} else {
 		err = sync_dirty_buffer(nilfs->ns_sbh[0]);
 	}

fs/nilfs2/the_nilfs.c

@@ -774,9 +774,7 @@ int nilfs_discard_segments(struct the_nilfs *nilfs, __u64 *segnump,
 			ret = blkdev_issue_discard(nilfs->ns_bdev,
 						   start * sects_per_block,
 						   nblocks * sects_per_block,
-						   GFP_NOFS,
-						   BLKDEV_IFL_WAIT |
-						   BLKDEV_IFL_BARRIER);
+						   GFP_NOFS, BLKDEV_IFL_WAIT);
 			if (ret < 0)
 				return ret;
 			nblocks = 0;
@@ -786,8 +784,7 @@ int nilfs_discard_segments(struct the_nilfs *nilfs, __u64 *segnump,
 		ret = blkdev_issue_discard(nilfs->ns_bdev,
 					   start * sects_per_block,
 					   nblocks * sects_per_block,
-					   GFP_NOFS,
-					  BLKDEV_IFL_WAIT | BLKDEV_IFL_BARRIER);
+					   GFP_NOFS, BLKDEV_IFL_WAIT);
 	return ret;
 }