Re: Xen bootloader (was: Re: [Xen-devel] Xen Roadmap proposal)

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> > IIRC, Linux kexec can boot other OSes in principle, so we should be able
> > to make this work for anything Linux can read the filesystem of.
>
> Which is a pretty serious restriction.

From the grub info page, supported filesystems are:
"BSD FFS", "DOS FAT16 and FAT32", "Minix fs", "Linux ext2fs", "ReiserFS", 
"JFS", "XFS", and "VSTa fs"

Of these, Linux supports: Minix, FAT*, Minix, Reiser, JFS, XFS  I understand 
that the Linux UFS driver can support a number of filesystems, including 
BSD's FFS.  I think there's some support for Solaris' UFS in there also.  The 
UFS driver had experimental write support last time I checked, but all that's 
really needed is basic read support to scrape the kernel off the disk.

There's also a Summer of Code project to make ZFS available as a FUSE 
filesystem, which grub can't support (at the moment...).  But until Solaris 
uses ZFS as a root fs this probably doesn't matter so much.

> I'm still not clear on why this
> is a preferable approach to modifying grub?

It's not necessarily a replacement for grub, but I think it'd be good to 
consider as an interim measure or as an alternative (there are already 
patches for kexec-under Xen floating around, so all we'd need to do in 
principle is to compile a kboot_sl ramdisk and run with it).

After all, it's not like there's a working grub port (that I know of) at the 
moment, so it's not like we lose anything ;-)

Is there anything I've missed in grub that's really not supported well enough 
to be done in Linux?

Cheers,
Mark


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