Syslinux - Apr 2014 - Bootloader data in /boot vs package systems (and atomic updates)

Hi,

I'm working on https://wiki.gnome.org/Projects/OSTree which is a 
general-purpose update system for Linux-based operating systems.  It 
isn't a package system itself, but operates at the same level.

A primary goal of OSTree is fully atomic updates, and the "swapped 
chroots" model works well for most of userspace and the 
kernel/initramfs.

However, syslinux relies on loadable modules in /boot.  At present in 
Fedora at least, the RPM package updates these, and it has a %post to 
ensure that when a newer version of extlinux is installed, we update 
both the boot modules and the MBR.

For more background, see:
https://bugzilla.redhat.com/show_bug.cgi?id=1090083

In constrat, GRUB2 keeps its modules in /usr/lib, and grub-install 
*copies* them to /boot at the same time that the MBR is updated.

I like this model more as it allows me to decouple the delivery of 
updated bootloader data with its actual installation, and ensure that 
when I do want to update the bootloader, it can happen at a safe(r) 
time.

Would there be any interest in patches for extlinux to support this 
model?

Any thoughts on the general topic?

On Tue, Apr 22, 2014 at 6:58 PM, Colin Walters <walters at verbum.org>
wrote:
> Hi,
>
> I'm working on https://wiki.gnome.org/Projects/OSTree which is a
> general-purpose update system for Linux-based operating systems.  It
isn't a
> package system itself, but operates at the same level.
>
> A primary goal of OSTree is fully atomic updates, and the "swapped
chroots"
> model works well for most of userspace and the kernel/initramfs.
>
> However, syslinux relies on loadable modules in /boot.  At present in
Fedora
> at least, the RPM package updates these, and it has a %post to ensure that
> when a newer version of extlinux is installed, we update both the boot
> modules and the MBR.
I think you mean the VBR since no Syslinux variant lives in the MBR
and on Linux, the MBR requires manual installation (outside executing
one of the installer binaries like linux/syslinux or
extlinux/extlinux; paths relative to source tree root in versions
before 6.00)
> For more background, see:
> https://bugzilla.redhat.com/show_bug.cgi?id=1090083
>
> In constrat, GRUB2 keeps its modules in /usr/lib, and grub-install *copies*
> them to /boot at the same time that the MBR is updated.
Does the installation of an updated package of GRUB2 trigger an
installation of modules during install on Fedora or does the
installation of an updated package require manual installation every
time?  Or is this perhaps a configuration?

The alternative is an additional script that would run the installer
binary extlinux and copy *.c32 at the same time.
> I like this model more as it allows me to decouple the delivery of updated
> bootloader data with its actual installation, and ensure that when I do
want
> to update the bootloader, it can happen at a safe(r) time.
This would also be a distinct departure from past behavior.
> Would there be any interest in patches for extlinux to support this model?
>
> Any thoughts on the general topic?
Unlike GRUB*, Syslinux will never be in the MBR and the post-MBR
sectors (aka hidden sectors or reserved sectors).  GRUB* can live
inside the partition entirely to allow a standard MBR but this is
dependent on file system and version.

-- 
-Gene

On Tue, Apr 22, 2014 at 8:16 PM, Gene Cumm <gene.cumm at gmail.com>
wrote:
> 
> I think you mean the VBR since no Syslinux variant lives in the MBR
> and on Linux, 
Right, thanks.
> Does the installation of an updated package of GRUB2 trigger an
> installation of modules during install on Fedora
It used to, but no longer does.  There's some background here:
https://bugzilla.redhat.com/show_bug.cgi?id=735259
> The alternative is an additional script that would run the installer
> binary extlinux and copy *.c32 at the same time.
Yeah, I'm considering changing at least the Fedora extlinux package to 
work this way.
> This would also be a distinct departure from past behavior.
Right, that's why I wanted to get feedback here first.  I'm not sure if 
other distributions have encountered this.  Maybe it doesn't matter 
much for traditional package systems as they're not robust against 
interruption at all anyways.

Colin Walters <walters at verbum.org> writes:
> I'm working on https://wiki.gnome.org/Projects/OSTree which is a
> general-purpose update system for Linux-based operating systems.  It
> isn't a package system itself, but operates at the same level.
>
> A primary goal of OSTree is fully atomic updates, and the "swapped
> chroots" model works well for most of userspace and the
> kernel/initramfs.
>
> However, syslinux relies on loadable modules in /boot.  At present in
> Fedora at least, the RPM package updates these, and it has a %post to
> ensure that when a newer version of extlinux is installed, we update
> both the boot modules and the MBR.
>
> For more background, see:
> https://bugzilla.redhat.com/show_bug.cgi?id=1090083
>
> In constrat, GRUB2 keeps its modules in /usr/lib, and grub-install
> *copies* them to /boot at the same time that the MBR is updated.
>
> I like this model more as it allows me to decouple the delivery of
> updated bootloader data with its actual installation, and ensure that
> when I do want to update the bootloader, it can happen at a safe(r)
> time.
>
> Would there be any interest in patches for extlinux to support this
> model?
I don't think vanilla extlinux (or generally, Syslinux) has anything to
do with this.  Some Fedora RPM packages might exhibit undesirable
behaviour, but you should bring that up with the package maintainer.
Syslinux upstream does not provide RPM packages, as far as I can see.

Moreover, the Syslinux package in Debian (and Archlinux, according to
Ady) does not put files into /boot, but leaves copying the modules to
some distro- (and packaging-) specific install script, which should fit
your purposes.

If you still need something supported in extlinux, please provide more
details.
-- 
Regards,
Feri.

On Apr 24, 2014 3:19 AM, "Ferenc Wagner" <wferi at niif.hu>
wrote:
>
> Colin Walters <walters at verbum.org> writes:
> > However, syslinux relies on loadable modules in /boot.  At present in
> > Fedora at least, the RPM package updates these, and it has a %post to
> > ensure that when a newer version of extlinux is installed, we update
> > both the boot modules and the MBR.
> I don't think vanilla extlinux (or generally, Syslinux) has anything to
> do with this.
syslinux.spec.in here:
http://git.kernel.org/cgit/boot/syslinux/syslinux.git/tree/syslinux.spec.in

--Gene