f2fs: enable flush_merge only in f2fs is not read-only

Enable flush_merge only in f2fs is not read-only, so does the mount
option show.
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/segment.c

@@ -1859,10 +1859,9 @@ int build_segment_manager(struct f2fs_sb_info *sbi)
 	sm_info->nr_discards = 0;
 	sm_info->max_discards = 0;
 
-	if (test_opt(sbi, FLUSH_MERGE)) {
+	if (test_opt(sbi, FLUSH_MERGE) && !f2fs_readonly(sbi->sb)) {
 		spin_lock_init(&sm_info->issue_lock);
 		init_waitqueue_head(&sm_info->flush_wait_queue);
-
 		sm_info->f2fs_issue_flush = kthread_run(issue_flush_thread, sbi,
 				"f2fs_flush-%u:%u", MAJOR(dev), MINOR(dev));
 		if (IS_ERR(sm_info->f2fs_issue_flush))

fs/f2fs/super.c

@@ -514,7 +514,7 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 {
 	struct f2fs_sb_info *sbi = F2FS_SB(root->d_sb);
 
-	if (!(root->d_sb->s_flags & MS_RDONLY) && test_opt(sbi, BG_GC))
+	if (!f2fs_readonly(sbi->sb) && test_opt(sbi, BG_GC))
 		seq_printf(seq, ",background_gc=%s", "on");
 	else
 		seq_printf(seq, ",background_gc=%s", "off");
@@ -542,7 +542,7 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 		seq_puts(seq, ",disable_ext_identify");
 	if (test_opt(sbi, INLINE_DATA))
 		seq_puts(seq, ",inline_data");
-	if (test_opt(sbi, FLUSH_MERGE))
+	if (!f2fs_readonly(sbi->sb) && test_opt(sbi, FLUSH_MERGE))
 		seq_puts(seq, ",flush_merge");
 	seq_printf(seq, ",active_logs=%u", sbi->active_logs);