[syslinux] syslinux and btrfs-formatted dos/MBR partition

[Gene Cumm]

On Tue, Jan 21, 2014 at 2:53 AM, David de Marneffe
<daviddemarneffe at gmail.com> wrote:
> Hello syslinux list,
>
> I have installed Arch over a btrfs-formatted dos/MBR primary
> partition* (no btrfs subvolumes, just installing everything including
> /boot in the root of the btrfs).
>
> I have been unsuccessful for several days trying to get it to boot
> with syslinux (6.02-8 package from Arch, also tried 4.07-1  Arch
> package). All I am getting is the copyright header line and a blinking
> cursor without keyboard control (can't type). No boot: prompt, no
> menu, no response to CTRL-ALT-DEL (have to power off to reboot).

So BIOS-mode boot.  If your config wants a menu (likely "UI menu.c32"
or the like), you will never see a prompt unless it fails to load.

> I am following the steps in Arch's beginner wiki and their syslinux
> page (tried both the script provided by Arch and the manual method).
> When I do this over ext4, everything works as expected, the copyright
> line appears briefly then the menu pops up. No go with btrfs no matter
> what I tried. So either it's a bug, or maybe I am repeatedly missing a
> step?

What 3-4 letter sequence do you see that indicates its disk access
mode?  It should be CHS or EDD.

> It looks to me like the ldlinux.sys code embedded in the first 64k of
> the btrfs partition crashes but no error message is generated. I have dd-ed
> the first 64k of the btrfs partition and compared the file in a hex
> editor with the ldlinux.sys file from an ext4 installation, and while
> no exactly identical it seems to me that ldlinux.sys gets correctly
> embedded as expected and does not overflow beyond the first 64k.

It won't be identical as the chunks are in differing volume offsets
and as a result the map and checksum differ.

How big is this disk?  Where is the beginning address?  Are you
installing a new MBR?  Are you doing any other steps outside those on
the wiki?

> Any insight would be appreciated. I have been advised to talk to
> Raphael_sc on irc about it, but I haven't managed to get a hold of him
> so far.

The only person I recall getting that advice was attempting to
chainload from Windows to a btrfs volume.

> * I am not using gpt because I want dual boot with winXP.

This should be OK as long as you're under the 2TiB limit on total disk
size and your BIOS cooperates.

-- 
-Gene