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Old 09-22-2011, 04:18 PM
Mark McLoughlin
 
Default grub / grub2 conflicts

On Thu, 2011-09-22 at 17:00 +0100, Matthew Garrett wrote:
> On Thu, Sep 22, 2011 at 04:50:16PM +0100, Mark McLoughlin wrote:
> > On Thu, 2011-09-22 at 14:05 +0100, Matthew Garrett wrote:
> > > The grub maintainer is telling you that the way in which you're trying
> > > to use grub is broken. You *need* to use the grub files that are in
> > > guest, not the host. This will be even more true with grub 2. It's not a
> > > matter of disliking the approach, it's a matter of it being demonstrably
> > > technically incorrect.
> >
> > There's nothing technically incorrect about the approach, demonstrably
> > or otherwise, if the version of grub in the guest and host is
> > compatible.
>
> grub provides no mechanism for you to know that, which means you can't
> reliably know that. Which means relying on them being compatible is
> incorrect.

You described yourself how libguestfs could check it. And failing
libguestfs doing it, the user could be warned to check it.

But again, all of this orthogonal to the issue of the Conflicts.

Whether the Conflicts is correct is a completely separate discussion
from how libguestfs should use grub and grub2.

Conflating the two discussions makes it appear like the maintainer of
one package is refusing to fix a bug in his package until another
maintainer agrees to change the design of his program to the first
maintainers taste.

Cheers,
Mark.

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Old 09-22-2011, 04:37 PM
Matthew Garrett
 
Default grub / grub2 conflicts

On Thu, Sep 22, 2011 at 05:18:09PM +0100, Mark McLoughlin wrote:
> On Thu, 2011-09-22 at 17:00 +0100, Matthew Garrett wrote:
> > grub provides no mechanism for you to know that, which means you can't
> > reliably know that. Which means relying on them being compatible is
> > incorrect.
>
> You described yourself how libguestfs could check it. And failing
> libguestfs doing it, the user could be warned to check it.

I described something that is, practically speaking, impossible.

> But again, all of this orthogonal to the issue of the Conflicts.
>
> Whether the Conflicts is correct is a completely separate discussion
> from how libguestfs should use grub and grub2.

There is no rational reason to have grub and grub2 installed on the same
system at once, and having them both there increases the complexity of
the system.

> Conflating the two discussions makes it appear like the maintainer of
> one package is refusing to fix a bug in his package until another
> maintainer agrees to change the design of his program to the first
> maintainers taste.

There's no bug in grub.
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Old 09-22-2011, 05:11 PM
Felix Miata
 
Default grub / grub2 conflicts

On 2011/09/22 17:37 (GMT+0100) Matthew Garrett composed:

> There is no rational reason to have grub and grub2 installed on the same
> system at once, and having them both there increases the complexity of
> the system.

For which definition of "system"? My systems typically contain 20 or more
partitions, of which 6 or more are /boot or / partitions on which Grub has
been installed, and all of which (except on Mac) contain DOS
compatible/legacy MBR code. I definitely don't need the additional complexity
that putting Grub2 on any of them would produce. It's bad enough
https://bugzilla.redhat.com/show_bug.cgi?id=107748 is nearly 8 years old with
no action.
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Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!

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Old 09-22-2011, 06:02 PM
David Airlie
 
Default grub / grub2 conflicts

> On Thu, Sep 22, 2011 at 05:18:09PM +0100, Mark McLoughlin wrote:
> > On Thu, 2011-09-22 at 17:00 +0100, Matthew Garrett wrote:
> > > grub provides no mechanism for you to know that, which means you
> > > can't
> > > reliably know that. Which means relying on them being compatible
> > > is
> > > incorrect.
> >
> > You described yourself how libguestfs could check it. And failing
> > libguestfs doing it, the user could be warned to check it.
>
> I described something that is, practically speaking, impossible.

you run rpm -q grub in the guest and on the host, if they are the same nvr,
then they are the same package, where's the rocket science here.

> There is no rational reason to have grub and grub2 installed on the
> same
> system at once, and having them both there increases the complexity
> of
> the system.

you can install KDE and GNOME and you are worrying about grub and grub2?

surely grubby could detect which one is actually in use and pick it without the world ending.

but I agree with Mark, you guys are completely conflating two very different things and using
one to justify the other.

the is no technical reason why grub and grub2 should conflict, if there is syslinux should also conflict.

Maybe I have a grub USB key I want to update with a new grub while my main MBR is grub2.

Dave.
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Old 09-22-2011, 06:18 PM
Matthew Garrett
 
Default grub / grub2 conflicts

On Thu, Sep 22, 2011 at 02:02:15PM -0400, David Airlie wrote:

> you run rpm -q grub in the guest and on the host, if they are the same nvr,
> then they are the same package, where's the rocket science here.

No, that's not good enough. You need to know the version installed on
the system, not the packaged version. Upgrading the package doesn't
cause grub-install to be rerun.

> > There is no rational reason to have grub and grub2 installed on the
> > same
> > system at once, and having them both there increases the complexity
> > of
> > the system.
>
> you can install KDE and GNOME and you are worrying about grub and grub2?

They don't both attempt to sit in the same few bytes.

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Old 09-22-2011, 06:18 PM
Peter Jones
 
Default grub / grub2 conflicts

On 09/22/2011 02:02 PM, David Airlie wrote:
>
>> On Thu, Sep 22, 2011 at 05:18:09PM +0100, Mark McLoughlin wrote:
>>> On Thu, 2011-09-22 at 17:00 +0100, Matthew Garrett wrote:
>>>> grub provides no mechanism for you to know that, which means you
>>>> can't
>>>> reliably know that. Which means relying on them being compatible
>>>> is
>>>> incorrect.
>>>
>>> You described yourself how libguestfs could check it. And failing
>>> libguestfs doing it, the user could be warned to check it.
>>
>> I described something that is, practically speaking, impossible.
>
> you run rpm -q grub in the guest and on the host, if they are the same nvr,
> then they are the same package, where's the rocket science here.

The whole point of libguestfs's usage was that the package isn't actually
installed in the guest. So that won't work.

The rest of your point ignores that grub1 is going away as soon as is
reasonably practicable.

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Old 09-22-2011, 06:38 PM
Adam Williamson
 
Default grub / grub2 conflicts

On Thu, 2011-09-22 at 17:18 +0100, Mark McLoughlin wrote:

> You described yourself how libguestfs could check it. And failing
> libguestfs doing it, the user could be warned to check it.

'check' it? And what's the user expected to do if they're incorrect?
Crowbar Ubuntu's grub2 into Fedora, or vice versa, so the host and the
guest will be compatible?

I hate to say it, but honestly, this thread looks pretty clear-cut to an
outsider: pjones and mjg59 are correct, and you and rwmj are incorrect.
Their arguments that it is fundamentally unsafe to use the host's grub
or, even more so, grub2 in a guest have clear merit, and it honestly
feels like the counter-arguments so far have been 'we've got away with
it so far' and 'doing it any other way is hard, and we already wrote all
this code, so please stop raising inconvenient questions'. Neither of
those arguments are at all compelling. I haven't seen a single serious
attempt to refute the central point that there is no guarantee of
compatibility between any particular two versions or even builds of grub
or grub2, and there is not even a mechanism for denoting and testing
compatibility. Given this, it's hard to see how it can possibly be the
right thing to do to use the host's grub or grub2 in the guest.

You have provided lots of arguments of the form 'but it would make
things so much easier for everyone if we could do that', but that's
really beside the point: it may be sad that you can't, but if you can't,
you can't. It's like saying "it'd be really cool if I could fly, so I'm
just gonna go ahead and jump off the side of this building". It's not
that anyone thinks it wouldn't be cool if you could fly, it's just that,
in point of fact, you can't.
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Old 09-22-2011, 06:38 PM
"Richard W.M. Jones"
 
Default grub / grub2 conflicts

On Thu, Sep 22, 2011 at 05:37:39PM +0100, Matthew Garrett wrote:
> On Thu, Sep 22, 2011 at 05:18:09PM +0100, Mark McLoughlin wrote:
> > On Thu, 2011-09-22 at 17:00 +0100, Matthew Garrett wrote:
> > > grub provides no mechanism for you to know that, which means you can't
> > > reliably know that. Which means relying on them being compatible is
> > > incorrect.
> >
> > You described yourself how libguestfs could check it. And failing
> > libguestfs doing it, the user could be warned to check it.
>
> I described something that is, practically speaking, impossible.

We allow you to inspect the guest to find the OS version, and even
versions of individual packages installed in it.

Using this you can make rules like "only apply grub-install to Fedora
guests <= version 15", or "only to guests that have grub version
between 1.A and 1.B".

http://libguestfs.org/guestfs.3.html#inspection

Rich.

PS. Also orthogonal to this discussion: It turns out that virt-v2v
doesn't use grub-install. However virt-v2v still needs some
development work to support grub2 configuration.

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Old 09-22-2011, 06:40 PM
Matthew Garrett
 
Default grub / grub2 conflicts

On Thu, Sep 22, 2011 at 07:38:54PM +0100, Richard W.M. Jones wrote:
> On Thu, Sep 22, 2011 at 05:37:39PM +0100, Matthew Garrett wrote:
> > I described something that is, practically speaking, impossible.
>
> We allow you to inspect the guest to find the OS version, and even
> versions of individual packages installed in it.

The package version of grub does nothing to tell you which version of
grub is actually installed in the boot sector.

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Old 09-22-2011, 06:41 PM
"Richard W.M. Jones"
 
Default grub / grub2 conflicts

On Thu, Sep 22, 2011 at 02:18:48PM -0400, Peter Jones wrote:
> On 09/22/2011 02:02 PM, David Airlie wrote:
> >
> >> On Thu, Sep 22, 2011 at 05:18:09PM +0100, Mark McLoughlin wrote:
> >>> On Thu, 2011-09-22 at 17:00 +0100, Matthew Garrett wrote:
> >>>> grub provides no mechanism for you to know that, which means you
> >>>> can't
> >>>> reliably know that. Which means relying on them being compatible
> >>>> is
> >>>> incorrect.
> >>>
> >>> You described yourself how libguestfs could check it. And failing
> >>> libguestfs doing it, the user could be warned to check it.
> >>
> >> I described something that is, practically speaking, impossible.
> >
> > you run rpm -q grub in the guest and on the host, if they are the same nvr,
> > then they are the same package, where's the rocket science here.
>
> The whole point of libguestfs's usage was that the package isn't actually
> installed in the guest. So that won't work.

This is not correct, grub is installed in the guest, but we don't want
to run it from the guest because of security problems. I outlined it
in an earlier email in this thread.

Rich.

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