nfs_getcacheblk
rabp = nfs_getcacheblk(vp, rabn, biosize, p);
bp = nfs_getcacheblk(vp, bn, biosize, p);
bp = nfs_getcacheblk(vp, 0, NFS_MAXPATHLEN, p);
bp = nfs_getcacheblk(vp, bn, biosize, p);
struct buf *nfs_getcacheblk(struct vnode *, daddr_t, int, struct proc *);