ffs_isblock
if (ffs_isblock(fs, blksfree, fragstoblks(fs, bno)))
if (ffs_isblock(fs, cg_blksfree(cgp), blkno)) {
int ffs_isblock(struct fs *, u_char *, daddr_t);
int ffs_isblock(struct fs *, u_char *, daddr_t);
if (ffs_isblock(fs, blksfree, fragstoblks(fs, bno)))
int ffs_isblock(struct fs *, u_char *, int32_t);