Index: usr.sbin/jail/command.c
===================================================================
--- usr.sbin/jail/command.c
+++ usr.sbin/jail/command.c
@@ -148,7 +148,8 @@
 		if (j->comstring == NULL || j->comstring->len == 0 ||
 		    (create_failed && (comparam == IP_EXEC_PRESTART ||
 		    comparam == IP_EXEC_CREATED || comparam == IP_EXEC_START ||
-		    comparam == IP_COMMAND || comparam == IP_EXEC_POSTSTART)))
+		    comparam == IP_COMMAND || comparam == IP_EXEC_POSTSTART ||
+		    comparam == IP_EXEC_PREPARE)))
 			continue;
 		switch (run_command(j)) {
 		case -1:
Index: usr.sbin/jail/config.c
===================================================================
--- usr.sbin/jail/config.c
+++ usr.sbin/jail/config.c
@@ -71,6 +71,7 @@
     [IP_EXEC_JAIL_USER] =	{"exec.jail_user",	PF_INTERNAL},
     [IP_EXEC_POSTSTART] =	{"exec.poststart",	PF_INTERNAL},
     [IP_EXEC_POSTSTOP] =	{"exec.poststop",	PF_INTERNAL},
+    [IP_EXEC_PREPARE] =		{"exec.prepare",	PF_INTERNAL},
     [IP_EXEC_PRESTART] =	{"exec.prestart",	PF_INTERNAL},
     [IP_EXEC_PRESTOP] =		{"exec.prestop",	PF_INTERNAL},
     [IP_EXEC_CREATED] =		{"exec.created",	PF_INTERNAL},
Index: usr.sbin/jail/jail.8
===================================================================
--- usr.sbin/jail/jail.8
+++ usr.sbin/jail/jail.8
@@ -726,6 +726,11 @@
 .Pp
 The pseudo-parameters are:
 .Bl -tag -width indent
+.It Va exec.prepare
+Command(s) to run in the system environment to prepare a jail for creation.
+These commands are executed before assigning IP addresses and before mounting
+filesystems, so they may be used to create a new jail filesystem if it does
+not already exist.
 .It Va exec.prestart
 Command(s) to run in the system environment before a jail is created.
 .It Va exec.created
Index: usr.sbin/jail/jail.c
===================================================================
--- usr.sbin/jail/jail.c
+++ usr.sbin/jail/jail.c
@@ -87,6 +87,7 @@
 
 static const enum intparam startcommands[] = {
     IP__NULL,
+    IP_EXEC_PREPARE,
 #ifdef INET
     IP__IP4_IFADDR,
 #endif
Index: usr.sbin/jail/jailp.h
===================================================================
--- usr.sbin/jail/jailp.h
+++ usr.sbin/jail/jailp.h
@@ -87,6 +87,7 @@
 	IP_EXEC_JAIL_USER,	/* Run jailed commands as this user */
 	IP_EXEC_POSTSTART,	/* Commands run outside jail after creating */
 	IP_EXEC_POSTSTOP,	/* Commands run outside jail after removing */
+	IP_EXEC_PREPARE,	/* Commands run outside jail before addrs and mounting */
 	IP_EXEC_PRESTART,	/* Commands run outside jail before creating */
 	IP_EXEC_PRESTOP,	/* Commands run outside jail before removing */
 	IP_EXEC_CREATED,	/* Commands run outside jail right after it was started */