sharing a partition betweed FC3 and FC5

[Paul Howarth]

On Sun, 2006-08-06 at 01:38 -0400, D. Hugh Redelmeier wrote:
> [I sent this to fedora-list at redhat.com a couple of minutes ago.  I 
> apologize for cross-posting.]
> 
> I installed 32-bit Fedora Core 5 on an Athlon-64 box.  I intended this
> installation to co-exist with a 64-bit Fedora Core 3 installation.
> The two installations share a /home ext3 partition and the swap partition.
> This is often how I do upgrades: a dual boot system with both old and
> new bootable.
> 
> The problem is that the FC5 installation did something to
> the /home partition that prevents the FC3 from mounting it.
> 
> When I manually try a mount of /home from FC3, the useless
> mount-failure message is preceded by these messages.  I think that
> they are the key:
> 
>     inode_doinit_with_dentry:  context_to_sid(system_u:object_r:home_root_t:s0) returned 22 for dev=hda5 ino=2
>     inode_doinit_with_dentry:  context_to_sid(system_u:object_r:home_root_t:s0) returned 22 for dev=hda5 ino=2
> 
> (In dmesg, these two messages were preceded by these that might be relevant:
>     kjournald starting.  Commit interval 5 seconds
>     EXT3 FS on hda5, internal journal
>     EXT3-fs: mounted filesystem with ordered data mode.
>     SELinux: initialized (dev hda5, type ext3), uses xattr
> )
> 
> (The useless mount failure message is:
>   mount: wrong fs type, bad option, bad superblock on /dev/hda5
>          or too many mounted file systems
>  This message is disgracefully non-specific.)
> 
> I think that this is a problem with SELinux.  The following thread
> looks relevant but unhelpful:
>   http://www.redhat.com/archives/fedora-selinux-list/2006-April/msg00002.html
> It provides a solution (I hope) for FC4 but FC3 would not have such an update.

I think you're right; the underlying issue is that FC5 file contexts
have 4 parts and FC4 and earlier have 3 parts (the extra part being for
MLS). The fix for FC4 was to apply a patch so that the kernel could deal
with (though probably not use) the MLS part. With FC3 now supported by
the Fedora Legacy project, who only usually do updates for security
issues, I think the chances of this getting fixed by them for FC3 are
slim to none.

You might be able to find the MLS patch in the FC4 kernel and see if you
could get it to apply on the FC3 kernel though.

> I tried using enforcing=0 on the FC3 kernel command line, but nothing changed.
> 
> I thought ext3 was compatible between Fedora releases.  Unfortunately,
> SELinux seems to have made things a lot more brittle.
> 
> ==> Is there something simple that I can do to allow the existing
>     /home ext3 partition to be shared between FC3 and FC5?

Can't think of any offhand.

Paul.