I'm trying to loopback mount an ISO image and then share it via HTTP.  This
needs the public_content_t type, so I tried to mount like:

 mount -t iso9660 -o context=system_u:object_r:public_content_t,ro,loop
/install/pub/fedora/linux/core/5/i386/iso/FC-5-i386-DVD.iso
/install/pub/fedora/linux/core/5/i386/os

That gives me (from dmesg):

ISO 9660 Extensions: Microsoft Joliet Level 3
ISO 9660 Extensions: RRIP_1991A
SELinux: security_context_to_sid(system_u:object_r:public_content_t) failed for
(dev loop0, type iso9660) errno=-22

Am I doing something wrong or is this a bug?

I thought I'd try to learn about the new modular SELinux, but I couldn't figure
out how to build a module to do that.