[U-Boot-Users] [RFC] Implementing Boot Image Fallback on U-Boot

[Matthias Fuchs]

Hi, 

take a look at Wolfgang's last posting from Tuesday on the 'intended behavior 
of bootm'. The bootlimit/altbootcmd function (in your case probably together 
with a hardware watchdog) could be the stuff you are (and I was) looking for.

Matthias

On Thursday 24 April 2008 04:53:48 Makito SHIOKAWA wrote:
> Boot Image Fallback is a mechanism that enables a system to fallback to a
> "known good" boot image in the event of catastrophic boot failure (i.e.
> failure to boot, panic on boot, failure to initialize HW/SW). (CGL
> Availability Requirements Definition V4.0: AVL.9.0). On system especially
> used in telecommunication, 99.999% high availability is required. So, this
> function is highly needed (like my customer requires).
>
> This time, I'm thinking of implementing Boot Image Fallback on U-Boot as
> follows (like a way GRUB does). So, I would appreciate any comments to
> this.
>
>
> It uses new U-Boot command "bootmf" and fw_setenv.
>
> * bootmf
>
> It is a wrapper of "bootm", and it boots kernel with fallback enabled on
> multiple kernel images.
>
>
> Also, it uses new U-Boot environment variables as follows.
>
> * imgaddr<N>
>
> It holds physical address of flash partition that kernel image is written.
> <N> is integer and becomes an entry of corresponding kernel image.
>
> (ex.) imgaddr0=0xf8000000, imgaddr1=0xf8200000
>
> * bootargs<N>
>
> It holds kernel parameter of entry <N>.
>
> (ex.) bootargs0=root=/dev/mtdblock1 , bootargs1=root=/dev/mtdblock3
>
> * default
>
> It holds default entry that "bootmf" tries to boot on default.
>
> (ex.) default=1
>
> * fallback
>
> It holds list of fallback entry that "bootmf" tries to boot on next if it
> fails to boot default entry.
>
> (ex.) fallback=1 2
>
>
> Now, I assume that circumstances are as follows. (In my case, Linux on
> Freescale MPC8540.)
>
> * There are three flash partitions "kernel-0", "kernel-1", "kernel-2" that
> kernel images are written.
>
> * Environment variables are set as follows.
>
> bootcmd=bootmf
> imgaddr0=0xf8000000 (physical address of "kernel-0")
> imgaddr1=0xf8200000 (physical address of "kernel-1")
> imgaddr2=0xf8400000 (physical address of "kernel-2")
> bootargs0=root=/dev/mtdblock1 (rootfs of "kernel-0")
> bootargs1=root=/dev/mtdblock3 (rootfs of "kernel-1")
> bootargs2=root=/dev/mtdblock5 (rootfs of "kernel-2")
> default=0
> fallback=1 2
>
> * "fw_setenv default 0" is written to /etc/rc.local.
>
>
> Then it behaves as follows.
>
> 1. When U-Boot boots up, "bootmf" is executed and tries to boot default
> entry in "default". Before booting kernel, "bootmf" sets corresponding
> fallback entry in "fallback" to "default". ((ex.) When booting entry "0",
> "1" is set and when booting entry "1", "2" is set.)
>
> 2. If kernel succeeds to boot, "default" is set to "0" by fw_setenv. So,
> next time U-Boot boots up and "bootmf" is executed, entry "0" will be
> booted again.
>
> 3. If kernel fails to boot, "default" stays to fallback entry "1" because
> fw_setenv won't be executed. So, next time U-Boot boots and "bootmf" is
> executed, fallback entry "1" will be booted.
>
>
> By this way, Boot Image Fallback on U-Boot can be realized. I recognize
> that this needs to rewrite flash each time booting a kernel, but I think
> there won't be so many reboots once stable system operation have started.
>
> I'll write and send a prototype of "bootmf" if it is needed.
>
>
> Best regards,
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