Mailinglist Archive: opensuse-bugs (2150 mails)

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[Bug 841247] Grub2 fails with btrfs

--- Comment #16 from Chris Murphy <bugzilla@xxxxxxxxxxxxxxxxx> 2014-04-16
04:33:20 UTC ---
(In reply to comment #14)
I did not actually create a bootable system, I was only trying to reproduce the
grub install failure in the original description, but in fact sdb6 contains
boot.img and core.img with no bootloader installation error. No "unusually
large" core.img message or failure to embed.

As for what's supported, I don't see how "do not install bootloader to the MBR"
is ever a supportable configuration. As soon as the user chooses this, they are
effectively choosing to create an unbootable system. To make it bootable
requires post-install configuration to chainload from a preexisting bootloader,
to the one installed in the VBR (e.g. sdb6 in my case). Nevertheless it seems a
bug somewhere that grub2-install failed with such error messages like in the
original description.

If there OP doesn't post the log for this failure, or no one can reproduce the
failure, then I think the bug could be closed for insufficient information.

(In reply to comment #15)
We don't modify upstream grub-install so probably some fedora patches make the
difference ?

Uncertain, I don't know the last time I even tested --force on Btrfs. Long
time. Maybe with 2.02-beta I'll try it but it's a weird use case IMO, and wow
what a hassle to support this long term.

Also, GRUB upstream prefers the use of a 1MB MBR gap or BIOS Boot over the
Btrfs bootloader pad.

IF your operating system too old (like Windoze XP) the partition tool with
partition in cylinder bounties and the size is determined by sectors per
In most case it's 63 sectors and you have only 32kB to use, far less than 1MB.

Yeah I understand. No matter what it means something must make use of the Btrfs
bootloader pad: extlinux does this explicitly by design, and GRUB2 does it
without complaint even though its devs prefer putting it somewhere else.

(it looks typically like comment#4). Plus the logical partition makes the
situation even worse .. (the logical partition and bootloader pad in it can't
be chainloaded by mbr directly ..).

I don't know if grub2 has an option for this, but boot.img always points to an
LBA. It's only a jump command, it doesn't tell the BIOS to "check MBR for
partition with active flag and go there". It seems to me it should be possible
to put boot.img in the MBR (wipe out the Windows stage1 bootloader) which then
points to the LBA for core.img which is e.g. /dev/sdb6 +2 (2nd sector in that
partition is the start of core.img, while the 1st sector is boot.img).

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