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Re: [Xen-users] Strange interaction from grub2 and XEN

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Strange interaction from grub2 and XEN
From: Marco Nenciarini <mnencia@xxxxxxxxxxxxxx>
Date: Mon, 23 Nov 2009 10:42:29 +0100
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Marco Nenciarini ha scritto:

I'm testing how xen and grub2 can work together.

I'm using xen 3.4.2 and grub2 1.97+20091115-1 from debian sid.

After many failed attempts I've discovered that on my system the first argument that grub2 should pass to the linux kernel is lost.

This is my working grub2 configuration:

menuentry "Xen 3.4.0 / Debian GNU/Linux, Linux 2.6.31-1-xen-amd64" {
    insmod xfs
    set root=(hd0,2)
    multiboot /boot/xen-3.4-amd64.gz
module /boot/vmlinuz-2.6.31-1-xen-amd64 dummy=dummy root=UUID=e9ed5af4-0503-4314-9d28-415a0eb7b0a0 ro quiet
    module /boot/initrd.img-2.6.31-1-xen-amd64
}

Looking in /proc/cmdline, there isn't any dummy=dummy argument

mnencia@manwe:/tmp$ cat /proc/cmdline
root=UUID=e9ed5af4-0503-4314-9d28-415a0eb7b0a0 ro quiet

Before the addition of dummy=dummy in front of line, the missing argument was the root=*, so my initrd had no idea of which root it have to mount.

BTW, the problem happens with both oldschool kernels and pvops ones.

I've googled around a bit, but I haven't found anything about this issue.

I've just found something on this issue in a debian bug report

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=555985#10

Here I quote the interesting part (Felix Zielcke talking of grub):

        With newest releases you have to double the filename both in multiboot
and module line or add a dummy parameter but the filename would reassemble GRUB Legacy's behaviour.
        I.e. with 1.97 change it to
            multiboot /xen-3.4-amd64.gz /xen-3.4-amd64.gz dom0_mem=512M
module /vmlinuz-2.6.31.5-xen-00513-g47dfde5 /vmlinuz-2.6.31.5-xen-00513-g47dfde5 nomodeset

So is a known issue/feature. Maybe some record of this are needed in xen wiki.

Kind Regards,
Marco

P.S: I'm still curious on why grub2 behaves in this manner.

--
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|    Marco Nenciarini    | Debian/GNU Linux Developer - Plug Member |
| mnencia@xxxxxxxxxxxxxx | http://www.prato.linux.it/~mnencia       |
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