Restore FreeBSD resource usage accounting

Add zfs_racct_* interfaces for platform-dependent read/write accounting.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #11613

include/sys/Makefile.am

@@ -110,6 +110,7 @@ COMMON_H = \
 	zfs_fuid.h \
 	zfs_project.h \
 	zfs_quota.h \
+	zfs_racct.h \
 	zfs_ratelimit.h \
 	zfs_refcount.h \
 	zfs_rlock.h \

include/sys/zfs_racct.h

@@ -0,0 +1,37 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Portions Copyright 2021 iXsystems, Inc.
+ */
+
+#ifndef _SYS_ZFS_RACCT_H
+#define	_SYS_ZFS_RACCT_H
+
+#include <sys/zfs_context.h>
+
+/*
+ * Platform-dependent resource accounting hooks
+ */
+void zfs_racct_read(uint64_t size, uint64_t iops);
+void zfs_racct_write(uint64_t size, uint64_t iops);
+
+#endif /* _SYS_ZFS_RACCT_H */