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Re: syslinux: updating in stretch?

Hi Lukas,

And thanks for your mail. I'm adding debian-boot@ for their information.

Lukas Schwaighofer <lukas@schwaighofer.name> (2017-10-17):
> as it turns out, syslinux in stretch is in a quite sorry state.  To
> summarize:
> 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:
>     https://bugs.debian.org/857597

It might be a good idea to have a bug report against syslinux as well,
which can be used for version tracking purposes, which is most
appreciated by people handling stable-proposed-updates requests (we
usually consider this mandatory, even if we sometimes let a few
exceptions go through).

> [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.

On top of the stretch package? It's always reassuring for stable release
managers to have people actually test packages for stable.

> 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.

That seems reassuring enough as far as I'm concerned.

> 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.

That seems like an appropriate course of action indeed.

> [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?

Your proposed changes fit the stable-proposed-updates criteria exactly,
with fixes in unstable, backports/cherry-picks to stretch already tested
and confirmed good, and reasonably-sized diffs. Really nice!

> * What kind of testing is required / expected so these changes can be
>   considered?

I think debian-cd@ is most qualified on this topic, I'm not sure d-i
uses syslinux for many things except for booting from an ISO anyway.
Consequently, what follows is just generic advice:

If you get a green light from debian-cd@, I think you only need to:
 - open a bug report for bug #3 (see my first paragraph);
 - open a pu request with a source debdiff against the package in
   stretch with an appropriate version number (probably
   3:6.03+dfsg-14.1+deb9u1); including as many details as in this
   mail would probably do the trick.


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