NFSv4: include bitmap in nfsv4 get acl data

The NFSv4 bitmap size is unbounded: a server can return an arbitrary
sized bitmap in an FATTR4_WORD0_ACL request.  Replace using the
nfs4_fattr_bitmap_maxsz as a guess to the maximum bitmask returned by a server
with the inclusion of the bitmap (xdr length plus bitmasks) and the acl data
xdr length to the (cached) acl page data.

This is a general solution to commit e5012d1f "NFSv4.1: update
nfs4_fattr_bitmap_maxsz" and fixes hitting a BUG_ON in xdr_shrink_bufhead
when getting ACLs.

Fix a bug in decode_getacl that returned -EINVAL on ACLs > page when getxattr
was called with a NULL buffer, preventing ACL > PAGE_SIZE from being retrieved.

Cc: stable@kernel.org
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
encode_getattr_three(struct xdr_stream *xdr,
		     uint32_t bm0, uint32_t bm1, uint32_t bm2,
		     struct compound_hdr *hdr)
{
	__be32 *p;

	p = reserve_space(xdr, 4);
	*p = cpu_to_be32(OP_GETATTR);
	if (bm2) {
		p = reserve_space(xdr, 16);
		*p++ = cpu_to_be32(3);
		*p++ = cpu_to_be32(bm0);
		*p++ = cpu_to_be32(bm1);
		*p = cpu_to_be32(bm2);
	} else if (bm1) {
		p = reserve_space(xdr, 12);
		*p++ = cpu_to_be32(2);
		*p++ = cpu_to_be32(bm0);
		*p = cpu_to_be32(bm1);
	} else {
		p = reserve_space(xdr, 8);
		*p++ = cpu_to_be32(1);
		*p = cpu_to_be32(bm0);
	}
	hdr->nops++;
	hdr->replen += decode_getattr_maxsz;
}

encode_getattr_three(struct xdr_stream *xdr,
		     uint32_t bm0, uint32_t bm1, uint32_t bm2,
		     struct compound_hdr *hdr)
{
	__be32 *p;

	p = reserve_space(xdr, 4);
	*p = cpu_to_be32(OP_GETATTR);
	if (bm2) {
		p = reserve_space(xdr, 16);
		*p++ = cpu_to_be32(3);
		*p++ = cpu_to_be32(bm0);
		*p++ = cpu_to_be32(bm1);
		*p = cpu_to_be32(bm2);
	} else if (bm1) {
		p = reserve_space(xdr, 12);
		*p++ = cpu_to_be32(2);
		*p++ = cpu_to_be32(bm0);
		*p = cpu_to_be32(bm1);
	} else {
		p = reserve_space(xdr, 8);
		*p++ = cpu_to_be32(1);
		*p = cpu_to_be32(bm0);
	}
	hdr->nops++;
	hdr->replen += decode_getattr_maxsz;
}
