Booting Android from sd card on Dream/G1

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Hi all,

Here are my findings about how to boot android from an SD card, useful for example to test development Android builds without messing your phone. This procedure was inspired by legacy GNU/Linux boot process and then should work on most hardware with a flashable recovery.

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I can't stress enough the fact that this procedure is targeted to experienced user. A good knowledge of linux/android booting process is more than required. This procedure is not meant to be useful to most people given its limitations (no recovery mode, rebuild of boot.img required)
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I won't propose a step by step tutorial as it's better to understand how to do it and adapt the procedure to each need.

Two modifications are required:
1. Declare to mount sd card partitions instead of internal flash volumes. This has to be done in the init.rc script.
For example:
mount yaffs2 mtd@system /system
mount yaffs2 mtd@system /system ro remount
with
mount ext2 /dev/block/mmcblk0p6 /system

2. For some reasons, in the boot process, sd card partitions generally show up later than the mount actions, so it is generally necessary to add a timer in init binary to give to to the kernel to detect sd card partitions before mounting them (adding a sleep(5) after the "A N D R O I D" text in init.c is enough).


Build your special boot.img embedding those two modifications and flash it on the recovery volume of your phone. Now, booting into recovery will launch the system on your sd.

Regards,

I would like to report success on booting the G1 from a system located on sd card (cyanogenmod 4.2.7.1). I will describe the procedure step by steps when every thing is okay.

There is just an issue that you might have encountered during cyanogenmod ROM cooking, all wireless connexions (wifi, BT, GSM) do not work. The same system on flash if okay. I made a diff on boot log messages and the only notable difference is this error :
E/MemoryHeapBase( 83): error opening /dev/pmem_gpu0: Permission denied
E/MemoryHeapBase( 83): error opening /dev/pmem_gpu1: Permission denied
E/MemoryHeapBase( 83): error opening /dev/hw3d: Permission denied

I tried to chmod 0555 /dev/pmem* with no success.... Any idea ?

Although I finally managed to have a usable system, this work is still experimental. Please fell free to test and report success, failures here so I can improve the thing.
Let's see how we can boot a copy of cyanogen ROM 4.2.7.1 located on sd card. The main purpose is to test future ROMs (eclair ?) without messing up your phone...


DISCLAIMER : This procedure is targeted to experienced user. I am not responsible if you loose your data, your phone or your Mom !


Prerequisites are :
- adb and fastboot operationnal on your host computer
- Boot image file boot.img :
http://www28.zippyshare.com/v/19654421/file.html
- files data.cpio.gz, system.cpio.gz (data.cpio.gz and system.cpio.gz are unmodified images of a fresh install of cyanogen ROM that fit the modified boot.img) from :
http://www15.zippyshare.com/v/57489279/file.html
http://www15.zippyshare.com/v/13077582/file.html


1.
Create 3 partitions on sd card. The first one (vfat) is to store your music, videos etc. The second and the third will hold /data and /system. Result shoul look like this :

# fdisk /dev/block/mmcblk0

Command (m for help): p

Disk /dev/block/mmcblk0: 1977 MB, 1977614336 bytes
64 heads, 63 sectors/track, 957 cylinders
Units = cylinders of 4032 * 512 = 2064384 bytes

Device Boot Start End Blocks Id System
/dev/block/mmcblk0p1 1 864 1741792+ c Win95 FAT32 (LBA)
/dev/block/mmcblk0p2 865 903 78624 83 Linux
/dev/block/mmcblk0p3 904 957 108864 83 Linux

Command (m for help):

2.
Copy data.cpio and system.cpio on the first partition of your sd card.

3.
Connect to your device with adb :
adb shell

4.
Mount mmcblk0p2 on temporary folder and extract user.cpio.gz archive :
mkdir /dev/tmp
mount /dev/block/mmcblk0p2 /dev/tmp
cd /dev/tmp
gunzip -c /sdcard/data.cpio.gz | cpio -i
cd /
umount /dev/tmp

5.
Mount mmcblk0p3 on temporary folder and extract system.cpio.gz archive :
mount /dev/block/mmcblk0p3 /dev/tmp
cd /dev/tmp
gunzip -c /sdcard/system.cpio.gz | cpio -i
cd /
umount /dev/tmp

6.
Reboot the phone in bootloader :
adb reboot bootloader

7.
Boot the phone with custom boot image :
unzip boot.img.zip
fastboot boot boot.img


Reports are welcome !

I haven't tried this, but great idea. Well done.

Maybe a nice additional idea would be a boot-menu style idea. Eg, detect OS on mem card and display a menu of "Internal" or "SD Card"?

I'm on it but as it will imply flashing people's phone, I need more testing and suggestions from experienced hackers. I only own my G1 for 5 days...

I acytually just started a thread about this in the Dream development subforum! :P
Some suggestions:
-Use a recovery image to boot the ROM on the sd card (look at modifying the CM recovery image) if this is possible. This way, you can boot from sd card when you want to, by booting into recovery image, without interfering with the flashed rom at all. No worries that flashin a new rom will require a reflash of your bootloader. Also, you can use the ROM installed in flash after a reboot without any hassle, which would be very useful when testing a ROM from the SD if it doesn't work very well and you need a working phone.

-Have the /data and /system-partition as folders on the 4th partition on the SD card, or as logical volumes on a primary one. Why?
Well, many people have their sd-cards set up with fat, extX, swap in that order. The partition layout you have described here simply isn't compatible with that, and will require a separate SD card just for this testing (which everyone might not have).

I must say, I think this is a GREAT idea! I so often want to test a few ROMS, but often they don't get the test-time they deserve because I need to swicth back to my working environment for job/uni the day after. This would be a great way to test a ROM thoroughly. And also it would be the best way to give a ROM a quick testdrive. switchroming back and forth is, for all its simplicity, hassle.

Using the recovery is the only way I found at the moment to boot from the sd card and was about to extend cm recovery with a dedicated menu Nevertheless, there will be a limitation with that: it will not be possible to use a different kernel for the system on sd as it will have to use the kernel of the recovery... Anyway, many custom roms around here use cm kernel (even those I saw with eclair) so it is not so problematic I think (tested Eugene373 AOSP20 yesterday). Anyway, it is possible to adapt the recovery with a test kernel...
I think I found a workaround for sd partitionning scheme pb, using bind mounts but I have not tested already. I will work on it this WE.

If I remember correctly you can use the command "reboot recovery" from the recovery shell to reboot again into recovery. It could mean that it is possible to choose what (kernel) to boot after the reboot. Even cyanogenmod has made quite a few changes to the kernel since the recovery image came out, and I think it would not be a very good solution to use the same kernel as the recovery image for all ROMs loaded via SD. (Especially the Hero ones won't work at all, I'm afraid.

It could also be possible maybe, to tweak the built-in bootloader into booting form either SD-card or from the internal flash? It already has the possibility to boot different things on different keypresses (home for recovery mode, and camera for fastboot). I have (again) no idea of its capabilities for reading anything off of the sd card, though.

I get your point naguz . I am not satisfied either with the solution of using the recovery kernel to boot the system on sd. I found that it adds quite much complexity to the init process: I tweaked the recovery executable to add an entry to boot from sd but I faced troubles in services startup and pre-init definitions. I think that the solution of using the recovery menu to choose to boot from sd have to be abandoned as it will require heavy additional changes to the init.rc scripts of the second system and will break its advanced features.

The ideal solution (as you suggested) would be to tweak the bootloader to boot natively from the sd card but unfortunately, we do not have the sources of the SPL (tell me if I am wrong) so it is definitely not possible.

The remaining solution is to use the recovery partition to flash the boot image of the second system. I works well, just press the home key and the second system boots ! The drawback is that you do not have recovery any more... Personnaly, I don't find that so problematic as I is still possible to boot a recovery image with fastboot when needed, so I think I will stick to this solution. I somebody have another solution, I am ok to investigate...

Aha, it makes sense that booting the sd directly from recovery mode would mess something up. I would think some of the same problems would be faced when booting the kernel from the recovery partiotion, doesn't it look like a different device to the kernel? Well, if it works, it works. :P

Regarding the source of the SPL, I have no idea, but I know hyakuro (a (former?) user here) has released a modified one. Trying to get in touch with him

As for the latest method: Is the recovery partiotion big enough to hold both the recovery image AND the kernel? If so, one could maybe have both. Maybe make a new "recovery image" that can either boot from sd or boot recovery image? Just throwing out ideas here.

Personally I don't see the big problem with not having a recovery image, as I would (in a dual-boot scenario) already have another, working install on the flash that I could use if the one booted from sd wasn't good enough. Re-flashing the recovery image could also be done from the working ROM in flash, for those without the SDK tools.

I think, however, that quite a few people will object to not having a recovery image.

Btw, was your latest working test done with one (4th) partition on the sd card for loading the ROM from SD? If so, new instructions please. I'd like to give it a try.