Re Molle and Carl-Daniel, some last words

Tue Mar 22 11:56:38 UTC 2005

On Tue, Mar 22, 2005 at 09:32:46AM +0100, Molle Bestefich wrote:
> Gerte Hoogewerf wrote:
> >> need to know: You can install GRUB just fine IFF you boot
> >> from a GRUB boot floppy. NEVER (except for trivial configurations)
> >> use the GRUB shell running under any operating system.
> >
> > Saying that (meaning: "IFF") would mean we would never be able to
> > install Linux using an installer. That's not true, so don't say it.
> 
> Hm, you're right.
> The patch is good if you want a Linux installer to be able to install
> on device-mapped devices.
> 
> Gerte, do you have the time to check that the patch is "clean" (I
> think it is), and perhaps vote +1 over on bug-grub for getting it
> included in GRUB?
> 
> 
> > (hd0,x) must be on (hd0) (duh!)
> 
> Well, as mentioned before, even though it's real simple, the GRUB
> stage2 simulator seems to screw it up.  I'll see if I can fix that bug
> another day.
> 
> 
> > I agree that installing grub is don't most safely when running the GRUB
> > shell in real-mode.
> 
> I think that dmraid should protect the HPT metadata blocks :-).

Well, it can't. GRUB needs fixing.

> 
> 
> >> and it destroyed my RAID0.
> >> GRUB is such a piece of crap :-).
> > GRUB is not a piece of crap. It's very very sensible when running it on
> > "unknown" things like the device-mapper stuff.
> 
> Right, sorry, just got a little worked up because it borked my RAID array again.
> 
> 
> > My experience is, you should always specify a (correct or in this case
> > empty) device-map when running grub:
> > /sbin/grub --device-map=/dev/null
> 
> Yes.  It seems, well, a bit dumb that the default in GRUB is to take a
> wild guess, assuming that's what it does if you don't tell it to relax
> and smoke a null file?
> 
> > Remember always to specify partitions (like: (hd0,x)) with with the grub
> > "device" command first and to specify the disk (like: (hd0)) in the last
> > place!!
> 
> Order shouldn't matter, that's a bug in GRUB as I see it.
> At least if we want GRUB to be user friendly.
> 
> > And don't ever blame me of installing bootloaders into (hd0,5),
> > I never recommend people to do this.
> 
> I'll just quote your web site,
> http://tienstra4.flatnet.tudelft.nl/~gerte/gen2dmraid/.
> === Installing grub on a /boot partition:
> # That's it, the rest should be easy:
> [...]
> grub> setup (hd0,0)
> ===
> Humn :-).
> (It isn't *exactly* (hd0,5), but isn't (hd0,0) equivalent?  or?)
> 
> 
> I'll just take the opportunity to thank you very much for the effort
> you put into helping others by making the gen2dmraid ISO images and
> the nice guides on your web site available.  They are a great help,
> thanks!
> 
> That said, could you perhaps share with us the LILO patch you use to
> make LILO work with device-mapped devices?  Your site only mentions
> that it "needs to be patched", no link to the patch.  Also, feel free
> to include my patch, it could be helpful for others wanting GRUB to
> work with dmraid from eg. inside the livecd or any booted Linux :-).
> 
> 
> > My last words on bootloaders and device-mapper stuff:
> > * I'm too busy to fix Saout's patch for Lilo to include straight
> > mappings.
> 
> I took a quick look, but can't figure out what's needed.
> Care to explain real quick?
> 
> 
> > * To make grub more dmraid-friendly, device-map code (asigning realmode
> > names to /dev names) {c,sh}ould be improved a tiny little bit.
> 
> Or just dropping the feature, seeing as there's no reasonably sane way
> to implement it for the foreseeable future.  Rather let the user know
> that he has to tell us, than to make some wild guess that's correct "a
> lot of the time" and turns your data into bitsoup the other half.
> 
> 
> > It could be an idea to make it less important in which order device commands are
> > given on the Grub shell.
> 
> Paramount to user friendliness, if you ask me.
> 
> Further, I think that the device (hdx,y) command should just be
> disallowed - as you said, (hdx,y) always resides on (hdx)!  Entering
> just device (hdx) instead of both (as seen in your example), works for
> me, so perhaps it's time to modify the example and remove the "device
> (hd0,0) /dev/blah" line?
> 
> 
> > * To make dmraid more accepted in the Linux world, we have to find a
> > generic way of (re-)reading partitiontables and giving names to devices
> > that might be 'something bootable'.
> 
> I seem to remember fdisk spewing out "Calling ioctl() to re-read
> partition tables" when you do part modifications under Linux.  What's
> wrong with doing the same with device-mapped devices?  Just tell the
> kernel to re-read partition tables?
> 
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-- 

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

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Heinz Mauelshagen                                 Red Hat GmbH
Consulting Development Engineer                   Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen at RedHat.com                            +49 2626 141200
                                                       FAX 924446
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