nfsd41: check encode size for sessions maxresponse cached

Calculate the space the compound response has taken after encoding the current
operation.

pad: add on 8 bytes for the next operation's op_code and status so that
there is room to cache a failure on the next operation.

Compare this length to the session se_fmaxresp_cached and return
nfserr_rep_too_big_to_cache if the length is too large.

Our se_fmaxresp_cached will always be a multiple of PAGE_SIZE, and so
will be at least a page and will therefore hold the xdr_buf head.
Signed-off-by: Andy Adamson <andros@netapp.com>
[nfsd41: non-page DRC for solo sequence responses]
[fixed nfsd4_check_drc_limit cosmetics]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[nfsd41: use cstate session in nfsd4_check_drc_limit]
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/nfs4xdr.c

@@ -3078,6 +3078,54 @@ static nfsd4_enc nfsd4_enc_ops[] = {
 	[OP_RECLAIM_COMPLETE]	= (nfsd4_enc)nfsd4_encode_noop,
 };
 
+/*
+ * Calculate the total amount of memory that the compound response has taken
+ * after encoding the current operation.
+ *
+ * pad: add on 8 bytes for the next operation's op_code and status so that
+ * there is room to cache a failure on the next operation.
+ *
+ * Compare this length to the session se_fmaxresp_cached.
+ *
+ * Our se_fmaxresp_cached will always be a multiple of PAGE_SIZE, and so
+ * will be at least a page and will therefore hold the xdr_buf head.
+ */
+static int nfsd4_check_drc_limit(struct nfsd4_compoundres *resp)
+{
+	int status = 0;
+	struct xdr_buf *xb = &resp->rqstp->rq_res;
+	struct nfsd4_compoundargs *args = resp->rqstp->rq_argp;
+	struct nfsd4_session *session = NULL;
+	struct nfsd4_slot *slot = resp->cstate.slot;
+	u32 length, tlen = 0, pad = 8;
+
+	if (!nfsd4_has_session(&resp->cstate))
+		return status;
+
+	session = resp->cstate.session;
+	if (session == NULL || slot->sl_cache_entry.ce_cachethis == 0)
+		return status;
+
+	if (resp->opcnt >= args->opcnt)
+		pad = 0; /* this is the last operation */
+
+	if (xb->page_len == 0) {
+		length = (char *)resp->p - (char *)xb->head[0].iov_base + pad;
+	} else {
+		if (xb->tail[0].iov_base && xb->tail[0].iov_len > 0)
+			tlen = (char *)resp->p - (char *)xb->tail[0].iov_base;
+
+		length = xb->head[0].iov_len + xb->page_len + tlen + pad;
+	}
+	dprintk("%s length %u, xb->page_len %u tlen %u pad %u\n", __func__,
+		length, xb->page_len, tlen, pad);
+
+	if (length <= session->se_fmaxresp_cached)
+		return status;
+	else
+		return nfserr_rep_too_big_to_cache;
+}
+
 void
 nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
 {
@@ -3094,6 +3142,9 @@ nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
 	BUG_ON(op->opnum < 0 || op->opnum >= ARRAY_SIZE(nfsd4_enc_ops) ||
 	       !nfsd4_enc_ops[op->opnum]);
 	op->status = nfsd4_enc_ops[op->opnum](resp, op->status, &op->u);
+	/* nfsd4_check_drc_limit guarantees enough room for error status */
+	if (!op->status && nfsd4_check_drc_limit(resp))
+		op->status = nfserr_rep_too_big_to_cache;
 status:
 	/*
 	 * Note: We write the status directly, instead of using WRITE32(),