ext4: include journal blocks in df overhead calcs

To more accurately calculate overhead for "bsd" style
df reporting, we should count the journal blocks as
overhead as well.
Signed-off-by: NEric Sandeen <sandeen@redhat.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
Tested-by: NEric Whitney <enwlinux@gmail.com>

fs/ext4/super.c

@@ -3231,6 +3231,10 @@ int ext4_calculate_overhead(struct super_block *sb)
 			memset(buf, 0, PAGE_SIZE);
 		cond_resched();
 	}
+	/* Add the journal blocks as well */
+	if (sbi->s_journal)
+		overhead += EXT4_B2C(sbi, sbi->s_journal->j_maxlen);
+
 	sbi->s_overhead = overhead;
 	smp_wmb();
 	free_page((unsigned long) buf);