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syslinux: updating in stretch?


as it turns out, syslinux in stretch is in a quite sorry state.  To

1. Booting from ext4 partitions created with Debian stretch does not
   work, because ext4's 64bit feature is enabled by default (since
   Debian stretch) and not supported by syslinux [1].
2. Booting from btrfs does not work [2].
3. A bug in the isolinux isohybrid MBR causing boot failures with some
   old BIOS [3].
4. Booting from xfs does not work (which was already the case in
   jessie, so not a regression in stretch) [4].

You will notice that this does not really leave any modern Unix
filesystem for syslinux/extlinux to boot from… from the above problems,
1-3 are a regression compared to Debian jessie.

[1] https://bugs.debian.org/833057
[2] https://bugs.debian.org/865462
[3] I didn't think to open a separate bug against syslinux, which would
    have been the right thing to do… the bug against debian-cd, which
    is affected by this problem, holds relevant information:
[4] https://bugs.debian.org/803938

Problems 1 and 2 have an upstream fix each [5, 6] which is pretty small
in size.  I'm able to locally reproduce each of the two problems and
also confirm that the respective patches fix the problems.

Problem 3 also has a small and self-contained upstream fix.  And
although I have no way to test this myself, the built isohdpfx.bin file
(with the fix applied) is identical to a known-good and tested version.

Problem 4 is fixed upstream as well (which I have not tested yet), but
the number of changes for that is pretty high.  Since this is both a
large patch and a not a regression from jessie, I don't intend to fix
this in Debian stretch.

[5] http://git.zytor.com/syslinux/syslinux.git/commit/?id=af7e95c32cea40c1e443ae301e64b27f068b4915
[6] http://git.zytor.com/syslinux/syslinux.git/commit/?id=548386049cd41e887079cdb904d3954365eb28f3

The current version in unstable contains the patches for 2 and 3
already and I've just requested sponsorship for another update which
also fixes 1.  Provided we do not find any regressions related to the
fixes for problems 1-3, I would like to push those patches [7, 8, 9] to
the version in Debian stretch in the next point release.

I know the next point release is still ~6 weeks off, but bootloader
changes are obviously critical.  So I wanted to raise this issue well
before the deadline to get an idea how (or if) I should proceed:

* Is this a reasonable request, or are these changes too dangerous
  for a point release anyways?
* What kind of testing is required / expected so these changes can be


[7] https://anonscm.debian.org/git/debian-cd/syslinux.git/tree/debian/patches/0016-btrfs-fix.patch?id=c61f3d0ef77ca726a0ff242c6ca6f1db90a8b9c6
[8] https://anonscm.debian.org/git/debian-cd/syslinux.git/tree/debian/patches/0017-isohdpfx.S-correct-heads-sectors.patch?id=c61f3d0ef77ca726a0ff242c6ca6f1db90a8b9c6
[9] https://anonscm.debian.org/git/debian-cd/syslinux.git/tree/debian/patches/0018-ext4-Fix-64bit-feature.patch?id=c61f3d0ef77ca726a0ff242c6ca6f1db90a8b9c6

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