NFSD: Make nfsd_genl_rqstp::rq_ops array best-effort

To enable NFSD to handle NFSv4 COMPOUNDs of unrestricted size,
resize the array in struct nfsd_genl_rqstp so it saves only up to
16 operations per COMPOUND.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: chucklever

fs/nfsd/nfsctl.c

@@ -1569,7 +1569,8 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
 				int j;
 
 				args = rqstp->rq_argp;
-				genl_rqstp.rq_opcnt = args->opcnt;
+				genl_rqstp.rq_opcnt = min_t(u32, args->opcnt,
+							    ARRAY_SIZE(genl_rqstp.rq_opnum));
 				for (j = 0; j < genl_rqstp.rq_opcnt; j++)
 					genl_rqstp.rq_opnum[j] =
 						args->ops[j].opnum;

fs/nfsd/nfsd.h

@@ -72,7 +72,7 @@ struct nfsd_genl_rqstp {
 
 	/* NFSv4 compound */
 	u32			rq_opcnt;
-	u32			rq_opnum[NFSD_MAX_OPS_PER_COMPOUND];
+	u32			rq_opnum[16];
 };
 
 extern struct svc_program	nfsd_programs[];