Index: lib/libc/sys/minherit.2
===================================================================
--- lib/libc/sys/minherit.2
+++ lib/libc/sys/minherit.2
@@ -29,7 +29,7 @@
 .\"
 .\"	@(#)minherit.2	8.1 (Berkeley) 6/9/93
 .\"
-.Dd October 30, 2007
+.Dd July 23, 2014
 .Dt MINHERIT 2
 .Os
 .Sh NAME
@@ -91,6 +91,11 @@
 after the parent forks and there is no way to get the previous
 shared-backing-store mapping without unmapping and remapping the address
 space in the parent.
+.It Dv INHERIT_ZERO
+This option causes the address space in question to be mapped as new
+anonymous pages,
+which would be initialized to all zero bytes,
+in the child process.
 .El
 .Sh RETURN VALUES
 .Rv -std minherit
@@ -130,6 +135,13 @@
 .Ox
 and then in
 .Fx 2.2 .
+.Pp
+The
+.Dv INHERIT_ZERO
+support first appeared in
+.Ox 5.6
+and then in
+.Fx 10.1 .
 .Sh BUGS
 Once you set inheritance to
 .Dv MAP_PRIVATE
Index: sys/sys/mman.h
===================================================================
--- sys/sys/mman.h
+++ sys/sys/mman.h
@@ -43,6 +43,7 @@
 #define INHERIT_SHARE	0
 #define INHERIT_COPY	1
 #define INHERIT_NONE	2
+#define INHERIT_ZERO	3
 #endif
 
 /*
Index: sys/vm/vm.h
===================================================================
--- sys/vm/vm.h
+++ sys/vm/vm.h
@@ -68,6 +68,7 @@
 #define	VM_INHERIT_SHARE	((vm_inherit_t) 0)
 #define	VM_INHERIT_COPY		((vm_inherit_t) 1)
 #define	VM_INHERIT_NONE		((vm_inherit_t) 2)
+#define	VM_INHERIT_ZERO		((vm_inherit_t) 3)
 #define	VM_INHERIT_DEFAULT	VM_INHERIT_COPY
 
 typedef u_char vm_prot_t;	/* protection codes */
Index: sys/vm/vm_map.c
===================================================================
--- sys/vm/vm_map.c
+++ sys/vm/vm_map.c
@@ -2228,6 +2228,7 @@
 	case VM_INHERIT_NONE:
 	case VM_INHERIT_COPY:
 	case VM_INHERIT_SHARE:
+	case VM_INHERIT_ZERO:
 		break;
 	default:
 		return (KERN_INVALID_ARGUMENT);
@@ -3343,6 +3344,31 @@
 			vm_map_copy_entry(old_map, new_map, old_entry,
 			    new_entry, fork_charge);
 			break;
+
+		case VM_INHERIT_ZERO:
+			/*
+			 * Clone the entry and link into the map.
+			 */
+			new_entry = vm_map_entry_create(new_map);
+			*new_entry = *old_entry;
+			/*
+			 * Copied entry is COW over the old object.
+			 */
+			new_entry->eflags &= ~(MAP_ENTRY_USER_WIRED |
+			    MAP_ENTRY_IN_TRANSITION | MAP_ENTRY_VN_WRITECNT);
+			new_entry->wiring_thread = NULL;
+			new_entry->wired_count = 0;
+			new_entry->object.vm_object = NULL;
+			new_entry->cred = NULL;
+			vm_map_entry_link(new_map, new_map->header.prev,
+			    new_entry);
+			vmspace_map_entry_forked(vm1, vm2, new_entry);
+			if (old_entry->cred != NULL) {
+				new_entry->cred = curthread->td_ucred;
+				crhold(new_entry->cred);
+				*fork_charge += (new_entry->end - new_entry->start);
+			}
+			break;
 		}
 		old_entry = old_entry->next;
 	}