[LEDE-DEV] Supporting crashdumps w/ kexec

[monster_philip at redfish-solutions.com]

> On Mar 8, 2017, at 8:32 PM, Luiz Angelo Daros de Luca <luizluca at gmail.com> wrote:
> 
> 1st: Is where does /boot get unmounted, and is there an easy way to
> keep it around a bit longer, at least until the init.d scripts have
> finished running?
> A: /boot (aka sda1) is never mounted on x86/x86_64. It could but it is
> simply unnecessary. grub is the only one that reads it (for loading
> grub confs and the kernel)
> 
> 2nd: Or what if I want to configure an extra menuentry in /boot/grub/grub.cfg?
> A: If you need to add extra kernel parameters, you simply need to
> mount sda1 somewhere (like /boot) and do as you would in a normal
> linux. You can edit grub conf there.
> 
> 3rd: how does a regular package force these kernel options?
> A: you can depend on a kernel config just like you depend on any other
> kernel config. CONFIG_KERNEL_XXX becomes CONFIG_XXX in kernel config.
> See procd makefile for reference. However, note that any selecting the
> package is enough to enable the config for any kernel compiled, even
> those that do not install your package.
> 
> 4th:  Is there an easy way to have the image include a 3rd partition
> for collecting crash dumps?
> A: your kexec package could configure the mounting. I don't know where
> is the best place for mounting, if /etc/fstab, /etc/config/fstab or
> mounting with a custom /etc/init.d/kexec service
> 
> 5th: what would be involved in mashing /dev/sda1 into the root unionfs?
> A: kernel could live inside rootfs. There is even an existing menu
> option (TARGET_ROOTFS_INCLUDE_KERNEL) for it (but not for x86). I
> guess grub2 can read files both from squashfs and ext4. Grub just need
> to look for the kernel there (you need to change the target partition
> from sda1 to sda2) and you must put the kernel inside sda2 and not
> sda1 during image build. The only drawback is that even if you change
> the kernel (writing to overlayfs), grub would still read from pristine
> squashfs. I don't know if this is really a problem because in
> LEDE/OpenWRT, you normally change kernel reflashing your system and
> not updating kernel.
> 
> I did some code (CC era) in order to put the kernel inside rootfs. It
> was used for a A/B upgrade strategy. grub conf was changed to boot
> either sda2 or sda3 rootfs. sysupgade could replace only the other
> rootfs partition or the whole system (boot+rootfs). It still misses
> some kind of hardware watchdog (I used a human watchdog). If there is
> interest for this particular A/B image solution (only for x86/x86_64
> and no watchdog), I can spend some time to bring it to LEDE trunk,
> 
> Regards,
> 
> ---
>     Luiz Angelo Daros de Luca, Me.
>            luizluca at gmail.com
> 
> _______________________________________________
> Lede-dev mailing list
> Lede-dev at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/lede-dev