getblkx
error = getblkx(vp, blkno, blkno, size, slpflag, slptimeo, flags, &buf);
int getblkx(struct vnode* vp, daddr_t blkno, daddr_t dblkno, int size, int slpflag, int slptimeo,
error = getblkx(vp, blkno, blkno, size, 0, 0, 0, &buf);