Index: sbin/mdmfs/mdmfs.8
===================================================================
--- sbin/mdmfs/mdmfs.8
+++ sbin/mdmfs/mdmfs.8
@@ -36,7 +36,7 @@
 driver
 .Sh SYNOPSIS
 .Nm
-.Op Fl DLlMNPStUX
+.Op Fl DLlMNPStTUX
 .Op Fl a Ar maxcontig
 .Op Fl b Ar block-size
 .Op Fl c Ar blocks-per-cylinder-group
@@ -52,6 +52,7 @@
 .Op Fl o Ar mount-options
 .Op Fl p Ar permissions
 .Op Fl s Ar size
+.Op Fl T Ar fstype
 .Op Fl v Ar version
 .Op Fl w Ar user : Ns Ar group
 .Ar md-device
@@ -231,6 +232,20 @@
 .Xr md 4
 device supports the BIO_DELETE command, enabling the TRIM on created
 filesystem allows return of freed memory to the system pool.
+.It Fl T Ar fstype
+Specify a file system type for a vnode-backed memory disk.
+The
+.Cm cd9660 ,
+.Cm ext2fs ,
+.Cm msdosfs ,
+and
+.Cm udf
+file systems are supported.
+This only makes sense if both
+.Fl F
+and
+.Fl P
+are specified.
 .It Fl U
 Enable soft-updates on the file system.
 This is the default, and is accepted only
@@ -293,7 +308,13 @@
 .Fl o
 option is passed to
 .Xr mount 8
-with the same letter.
+with the same letter;
+the
+.Fl T
+option is passed to
+.Xr mount 8
+as
+.Fl t .
 See the programs that the options are passed to for more information
 on their semantics.
 .Sh EXAMPLES
@@ -334,6 +355,10 @@
 using automatic device numbering:
 .Pp
 .Dl "mdmfs -P -F foo.img mds1a /tmp/"
+.Pp
+Mount a vnode-backed cd9660 file system using automatic device numbering:
+.Pp
+.Dl "mdmfs -T cd9660 -P -F foo.iso md /tmp"
 .Sh COMPATIBILITY
 The
 .Nm
Index: sbin/mdmfs/mdmfs.c
===================================================================
--- sbin/mdmfs/mdmfs.c
+++ sbin/mdmfs/mdmfs.c
@@ -80,6 +80,7 @@
 static void	 do_mdconfig_detach(void);
 static void	 do_mount(const char *, const char *);
 static void	 do_mtptsetup(const char *, struct mtpt_info *);
+static int	 valid_fstype(const char *fstype);
 static void	 do_newfs(const char *);
 static void	 extract_ugid(const char *, struct mtpt_info *);
 static int	 run(int *, const char *, ...) __printflike(2, 3);
@@ -129,7 +130,7 @@
 	}
 
 	while ((ch = getopt(argc, argv,
-	    "a:b:Cc:Dd:E:e:F:f:hi:LlMm:NnO:o:Pp:Ss:tUv:w:X")) != -1)
+	    "a:b:Cc:Dd:E:e:F:f:hi:LlMm:NnO:o:Pp:Ss:tT:Uv:w:X")) != -1)
 		switch (ch) {
 		case 'a':
 			argappend(&newfs_arg, "-a %s", optarg);
@@ -218,6 +219,11 @@
 		case 't':
 			argappend(&newfs_arg, "-t");
 			break;
+		case 'T':
+			if (!valid_fstype(optarg))
+				usage();
+			argappend(&mount_arg, "-t %s", optarg);
+			break;
 		case 'U':
 			softdep = true;
 			break;
@@ -500,6 +506,23 @@
 	}
 }
 
+static int
+valid_fstype(const char *fstype)
+{
+	unsigned int i;
+	static const char *fs[] = {
+	"cd9660", "ext2fs", "msdosfs", "udf",
+	NULL
+	};
+
+	for (i = 0; fs[i] != NULL; ++i) {
+		if (strcmp(fstype, fs[i]) == 0)
+			return (1);
+	}
+
+	return (0);
+}
+
 /*
  * Put a file system on the memory disk.
  */