diff --git a/sys/sys/_iovec.h b/sys/sys/_iovec.h
index 72642e5227c5..9a4eedc80b4f 100644
--- a/sys/sys/_iovec.h
+++ b/sys/sys/_iovec.h
@@ -1,47 +1,71 @@
 /*-
  * SPDX-License-Identifier: BSD-3-Clause
  *
  * Copyright (c) 1982, 1986, 1993, 1994
  *	The Regents of the University of California.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  * 3. Neither the name of the University nor the names of its contributors
  *    may be used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #ifndef _SYS__IOVEC_H_
 #define	_SYS__IOVEC_H_
 
 #include <sys/_types.h>
 
 #ifndef _SIZE_T_DECLARED
 typedef	__size_t	size_t;
 #define	_SIZE_T_DECLARED
 #endif
 
 struct iovec {
 	void	*iov_base;	/* Base address. */
 	size_t	 iov_len;	/* Length. */
 };
 
+#ifdef _KERNEL
+#define	IOVEC_INIT(iovp, base, len) 					\
+	*(iovp) = (struct iovec){ .iov_base = (base), .iov_len = (len) }
+
+/* String with length including NUL terminator */
+#define	IOVEC_INIT_CSTR(iovp, str)	do {				\
+	void *__str = (str);						\
+	IOVEC_INIT(iovp, __str, strlen(__str) + 1);			\
+} while(0)
+
+/* Object with size from sizeof() */
+#define	IOVEC_INIT_OBJ(iovp, obj)					\
+	IOVEC_INIT(iovp, &(obj), sizeof(obj))
+
+#define	IOVEC_ADVANCE(iovp, amt)	do {				\
+	struct iovec *__iovp = (iovp);					\
+	size_t __amt = (amt);						\
+	KASSERT(__amt <= __iovp->iov_len, ("%s: amount %zu > iov_len	\
+	    %zu", __func__, __amt, __iovp->iov_len));			\
+	__iovp->iov_len -= __amt;					\
+	__iovp->iov_base = (char *)__iovp->iov_base + __amt;		\
+} while(0)
+#endif /* _KERNEL */
+
 #endif /* !_SYS__IOVEC_H_ */