I have some progress booting Maemo 5 from mmc card. Bootmenu did not work for me so I was editing /sbin/preinit. So far I've managed to switch the root filesystem to card at boot time and start the init there. But there are some problems.
Firs of all is it really necessary to do
in the /etc/init.d/rcS script? Everything here is mounted in /sbin/preinit script.

Another strange thing is that in /sbin/preinit pivot_root is done without moving the parts of filesystem that are already mounted. If it is not done than i suppose we should mount them again as it is done in /etc/init.d/rcS if the root has been changed (but i think than they will be mounted two times in old root and new). But if we are booting from internal flash i think it will generate warnings. I think the right way id to remove mounts from /etc/init.d/rcS and do the pivot_root somehow like this:
So how and where should mounting be handled correctly during the boot from card?

I've got past the /etc/init.d/rcS script during the boot process from card. The screen shows that the devise is booting (first it starts the boot animation, then the screen goes blank and indicator flashes yellow and green, then it starts playing the animation but noting happens after that). Which stage of the boot process is that? How can I get the system boot log at that time?
I see that the /etc/init.d/rc script stops all the scripts in /etc/rc?.d/ but which script starts them? (so that i can add some output in that script and see on which script the system hangs).

For good measure, you did see that I corrected the bootmenu deb URL? the old one was faulty.

You would want to flash a fbcon enabled kernel and disable the boot animation to track it. As well as adjusting console= parameter in CONFIG_CMDLINE to tty0 only.

Yes I saw the right link. My preinit script now does pretty much the same as bootmenu (only I added some more output for testing). I think it should work the same now as the problem is actually somewhere in startup scripts in the original system.
Where can I get precompiled kernel with fbcon enabled? I was trying to recompile the kernel. If I don't change options from the original rx51 default config it boot fine, but I couldn't get a working version if i change something.

Could you put your preinit patches somewhere btw?

Do you recompile in the FREMANTLE_ARMEL target? Someone had luck enabling CONFIG_FBCON=y.

Here is my version of preinit that at least start to boot from card:
http://sr.uz/tmp/preinit
I constantly change it (vi on the devise saves me). So the most useful from it right now would be the list of kernel modules in the right order to load and some ideas on what to do with mounted parts of file system (described in the first post). There is no debug output in it because I moved one to startup scripts. I was saving dmesg output and monitoring devises here.

I've compiled it in the FREMANTLE_ARMEL target with no additional options and outside the scratchbox with ARCH and CROSS_COMPILE options defined. The results were the same. With default settings produced kernel works fine (it even worked when I disabled some debug options). By the whay “make ARCH=arm CROSS_COMPILE=/scratchbox/compilers/cs
2007q3-glibc2.5-arm7/bin/arm-none-linux-gnueabi- menuconfig” only worked outside the scratchbox. I will try my luck compiling the kernel tomorrow.

ps. At least for now I managed to move /usr to the card

Sorry. I'm a noob when it comes ti Maemo/Linux.

What benefits or possibilities do booting off MicroSD give? =)

First of all you will have more free space in you root partition. There is ~228Mb of free space in internal flash memory. Only /opt is on memory card. Most of the programs are installed in /opt but they also use some space in internal memory. Even in guidelines for building programs for maemo it is stated that it is ok to use up to 500kb of space in internal memory for program. And some programs just can't be installed in /otp. I have already run into free space limit in internal memory installing programs.
Another advantage is that you can make system backup by coping the content of the card. It will save the exact state of the system with all the programs and configurations. I am not sure that backup utility can save all the changes that were made in internal memory (it's purpose is mainly to save contacts and phone configuration).
You can also boot other distributions like Mer from card. You can even have not only one system installed on the card and you will be able to chose witch one to load.
Internal NAND memory has number of erase-write cycles. This number is big but is possible to ware off the internal memory. And you can't replace it. If you ware off your card you can get a new one.

I would love to help here but I still don't have real device.


BTW, the mount --move look like the way but I am not sure if busybox allows it. If not, it is possible to use '-o bind', that's how it is done with /tmp in previous tablets because /tmp already has critical files/sockets there (bme, dsme). After pivot_root is done and /sbin/init is exec-ed in new root, there is 'mount -n -o bind /mnt/initfs/tmp /tmp' in /etc/init.d/rcS for previous tablets.

Not sure about N900 but maybe there is something important in /tmp (or elsewhere) too?

Other filesystem (/proc, /sys, /dev/pts ...) can be simply mounted again and old versions unmounted when no longer needed.
EDIT: it should not be needed to to any such changes, please ignore all in italic above and see later post

BTW, I managed to extract N900 firmware image and checked /sbin/preinit etc. but still having the device would be invaluable here.

Silly question, do you mount your MMC rootfs read-write?

Looks like N900 was developed with initfs in place just like previous tablets and it was disabled relatively late in development. So there is lot of code which make sense with initfs but which is just skipped in current state. This makes it more confusing but hopefully it makes it more likely to work when going back to having separate initfs or switching to mmc via pivot_root.

From current /sbin/preinit code it looks like pivot_root is not done at all when booting default system from flash. By default root_mounted=1 so the boot() code skips the pivot root completely.

But still fini_system is always called so /proc /sys /tmp etc. is unmounted and needs to be mounted again in new root. So when thinking more about it, it looks simpler in N900 version and no modifications of /etc/init/d/rcS should be needed in copied system. It should expect that nothing is mounted and nothing is running and should do everything again. So it also means there is no trouble with /tmp. So I wonder what problem you are having when starting cloned system.