mount_ext2fs returning ENODEV on 6.1

[Perry Hutchison]

> > # ll /dev/ad0s7
> > crw-r-----  1 root  operator    0,  93 Sep  4 02:30 /dev/ad0s7
> > # file -s /dev/ad0s7
> > /dev/ad0s7: Linux rev 1.0 ext2 filesystem data
> > # grep -w ad0s7 /etc/fstab
> > /dev/ad0s7      /linux          ext2fs  ro              0       0
> > # ll -d /linux
> > drwxr-xr-x  2 root  wheel  512 Aug 24 12:09 /linux
> > # mount /linux
> > mount_ext2fs: /dev/ad0s7: Operation not supported by device
> 
> No ext2fs support in your kernel?

I had not thought that was the problem, since according to
something in the docs or manpages -- which I now cannot locate
-- missing kernel support should have resulted in a different
message.  How would I check, to be sure?  I am using the kernel
from the installation CD, not one I have built:

# uname -a
FreeBSD fbsd61 6.1-RELEASE FreeBSD 6.1-RELEASE #0: Sun May  7 04:32:43 UTC 2006     root at opus.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  i386