nfsd: further centralize protocol version checks.

With this patch the only places that test ->rq_vers against a specific
version are nfsd_v4client() and nfsd_set_fh_dentry().
The latter sets some flags in the svc_fh, which now includes:
  fh_64bit_cookies
  fh_use_wgather
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfsfh.c

@@ -284,13 +284,17 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp)
 	case 4:
 		if (dentry->d_sb->s_export_op->flags & EXPORT_OP_NOATOMIC_ATTR)
 			fhp->fh_no_atomic_attr = true;
+		fhp->fh_64bit_cookies = true;
 		break;
 	case 3:
 		if (dentry->d_sb->s_export_op->flags & EXPORT_OP_NOWCC)
 			fhp->fh_no_wcc = true;
+		fhp->fh_64bit_cookies = true;
 		break;
 	case 2:
 		fhp->fh_no_wcc = true;
+		if (EX_WGATHER(exp))
+			fhp->fh_use_wgather = true;
 	}
 
 	return 0;

fs/nfsd/nfsfh.h

@@ -88,6 +88,8 @@ typedef struct svc_fh {
 						 * wcc data is not atomic with
 						 * operation
 						 */
+	bool			fh_use_wgather;	/* NFSv2 wgather option */
+	bool			fh_64bit_cookies;/* readdir cookie size */
 	int			fh_flags;	/* FH flags */
 	bool			fh_post_saved;	/* post-op attrs saved */
 	bool			fh_pre_saved;	/* pre-op attrs saved */

fs/nfsd/vfs.c

@@ -1162,7 +1162,6 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 	errseq_t		since;
 	__be32			nfserr;
 	int			host_err;
-	int			use_wgather;
 	loff_t			pos = offset;
 	unsigned long		exp_op_flags = 0;
 	unsigned int		pflags = current->flags;
@@ -1188,12 +1187,11 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 	}
 
 	exp = fhp->fh_export;
-	use_wgather = (rqstp->rq_vers == 2) && EX_WGATHER(exp);
 
 	if (!EX_ISSYNC(exp))
 		stable = NFS_UNSTABLE;
 
-	if (stable && !use_wgather)
+	if (stable && !fhp->fh_use_wgather)
 		flags |= RWF_SYNC;
 
 	iov_iter_kvec(&iter, ITER_SOURCE, vec, vlen, *cnt);
@@ -1212,7 +1210,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 	if (host_err < 0)
 		goto out_nfserr;
 
-	if (stable && use_wgather) {
+	if (stable && fhp->fh_use_wgather) {
 		host_err = wait_for_concurrent_writes(file);
 		if (host_err < 0)
 			commit_reset_write_verifier(nn, rqstp, host_err);
@@ -2181,8 +2179,7 @@ nfsd_readdir(struct svc_rqst *rqstp, struct svc_fh *fhp, loff_t *offsetp,
 	loff_t		offset = *offsetp;
 	int             may_flags = NFSD_MAY_READ;
 
-	/* NFSv2 only supports 32 bit cookies */
-	if (rqstp->rq_vers > 2)
+	if (fhp->fh_64bit_cookies)
 		may_flags |= NFSD_MAY_64BIT_COOKIE;
 
 	err = nfsd_open(rqstp, fhp, S_IFDIR, may_flags, &file);