Index: sys/conf/files
===================================================================
--- sys/conf/files
+++ sys/conf/files
@@ -3182,6 +3182,7 @@
 # routines may be optimized for a particular platform.  In either case,
 # the file should be moved to conf/files.<arch> from here.
 #
+libkern/asprintf.c		standard
 libkern/arc4random.c		standard
 libkern/bcd.c			standard
 libkern/bsearch.c		standard
Index: sys/libkern/asprintf.c
===================================================================
--- /dev/null
+++ sys/libkern/asprintf.c
@@ -0,0 +1,77 @@
+/*-
+ * Copyright (c) 2013-2015 Sandvine Inc.  All rights reserved.
+ * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/malloc.h>
+
+#include <machine/stdarg.h>
+
+int
+vasprintf(char **buf, struct malloc_type *mtp, const char *format, va_list va)
+{
+	int len, ret;
+	va_list tmp_va;
+	char dummy;
+
+	va_copy(tmp_va, va);
+	len = vsnprintf(&dummy, 0, format, tmp_va);
+	va_end(tmp_va);
+	if (len < 0) {
+		*buf = NULL;
+		return (len);
+	}
+
+	/* Account for null terminator. */
+	len += 1;
+	*buf = malloc(len, mtp, M_NOWAIT);
+	if (*buf == NULL)
+		return (-1);
+
+	ret = vsnprintf(*buf, len, format, va);
+	if (ret < 0) {
+		free(*buf, mtp);
+		*buf = NULL;
+	}
+
+	return (ret);
+}
+
+int
+asprintf(char **buf, struct malloc_type *mtp, const char *format, ...)
+{
+	int ret;
+	va_list va;
+
+	va_start(va, format);
+	ret = vasprintf(buf, mtp, format, va);
+	va_end(va);
+
+	return (ret);
+}
Index: sys/sys/systm.h
===================================================================
--- sys/sys/systm.h
+++ sys/sys/systm.h
@@ -205,11 +205,15 @@
 	    __va_list) __printflike(1, 0);
 void	log(int, const char *, ...) __printflike(2, 3);
 void	log_console(struct uio *);
+int	asprintf(char **ret, struct malloc_type *mtp, const char *format, 
+	    ...) __printflike(3, 4);
 int	printf(const char *, ...) __printflike(1, 2);
 int	snprintf(char *, size_t, const char *, ...) __printflike(3, 4);
 int	sprintf(char *buf, const char *, ...) __printflike(2, 3);
 int	uprintf(const char *, ...) __printflike(1, 2);
 int	vprintf(const char *, __va_list) __printflike(1, 0);
+int	vasprintf(char **ret, struct malloc_type *mtp, const char *format,
+	    __va_list ap) __printflike(3, 0);
 int	vsnprintf(char *, size_t, const char *, __va_list) __printflike(3, 0);
 int	vsnrprintf(char *, size_t, int, const char *, __va_list) __printflike(4, 0);
 int	vsprintf(char *buf, const char *, __va_list) __printflike(2, 0);