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

[David de Marneffe]

Hello Gene, thanks for your reply.

Yes BIOS mode. The config wants a menu, which loads fine under ext4
and not under btrfs. Under btrfs I have also tried to remove the
syslinux.cfg file altogether (which should trigger the boot: prompt if
I am not mistaken) and the result is the same: only the copyright line
appears and no prompt.

The three letter sequence is EDD.

The disk is 160GB, here is the fdisk. Tried to install on /dev/sda6
and /dev/sda3.

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders, total 312581808 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x92e4538c

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1              63   167750729    83875333+   7  HPFS/NTFS/exFAT
/dev/sda2       167750791   296093695    64171452+   f  W95 Ext'd (LBA)
/dev/sda3   *   296094015   312496379     8201182+  83  Linux
/dev/sda4       312496380   312576704       40162+  ef  EFI (FAT-12/16/32)
/dev/sda5       167750793   259915634    46082421    7  HPFS/NTFS/exFAT
/dev/sda6       259917824   296093695    18087936   83  Linux

It's true I am normally chainloading my Linux installations from the
WinXP bootloader, and that is what I initially tried with my btrfs
attempts, however in the course of testing I just backed up my MBR and
let syslinux overwrite it (yes I did set the boot flag before
installing syslinux and overwriting the MBR). That didn't make any
difference.

I am not performing any extra steps (although I tried adding hooks etc
but it didn't work). Simply put, if I follow the Arch wiki step by
step and format with ext4, everything works as expected. If I do the
same with btrfs, it's a no-no.

On 21/01/2014, Gene Cumm <gene.cumm at gmail.com> wrote:
> 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
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