ext4_decode_error
extern const char *ext4_decode_error(struct super_block *sb, int errno,
const char *errstr = ext4_decode_error(NULL, err, nbuf);
seq_printf(seq, "#%-5u: %s\n", group, ext4_decode_error(NULL, err, nbuf));
errstr = ext4_decode_error(sb, j_errno, nbuf);
errstr = ext4_decode_error(sb, errno, nbuf);