[Buildroot] Creating/installing images

Willy Lambert lambert.willy at gmail.com
Thu Dec 13 01:08:39 UTC 2012

2012/12/12 Thomas Petazzoni <thomas.petazzoni at free-electrons.com>:
> Dear Willy Lambert,
> On Wed, 12 Dec 2012 22:28:10 +0100, Willy Lambert wrote:
>> I was using for my embedded system a standard debian + a set of
>> apt-get to get a customized OS on a 2GB on board persistent memory (so
>> I have a working system, as kernel config for instance). But now I
>> decided to dive into the wonderfull world of "linux from scratch" with
>> the great help of busybox in order to :
>> _ know exactly what's on my board
>> _ reduce persistent size
>> _ stop doing overkill with a 2GB system that can fit in 32Mb
>> So I have setup busybox and spent some days into documentation and
>> sandbox, but I'm stuck with the target image installation. The
>> documentation stops at this point and I'm alone in the dark. I spent 2
>> days in searching docs on the internet without great success.
>> I have a successful qemu working to test the buildroot output, cause I
>> don't need bootloader or proper image, just giving bzImage and
>> rootfs.ext2 is enougth.
>> But as to create something that my embedded system can boot on .... I
>> really don't know what and how to do. So I would be glad if anyone
>> could help me, at least in giving links or keyword for documentation.
>> My target has an onboard flash memory. World would have been simplier
>> if I could have a removable "root" memory but it's not the case. So If
>> I'm correct I need to boot my target (either with an external boot
>> device like usb key, or with the existing linux installed on it) and
>> then replace the rootfs. What would you do in this case (knowing that
>> it will happen often in the dev cycle) ?
>> _ use a ram pivot_root from the current linux?
>> _ use a dd from an external usb key boot ?
>> _ re-partition all this to have a little 10Mb part for a "Tool OS"
>> that can be used for rootfs installation ?
>> _ do somethig else ?
>> _ take a beer and think more ?
> I would use the capacity of your board to boot over the network. Since
> it is a x86 platform with a BIOS, I guess it is capable of doing PXE.
> So during development, I would load the kernel using PXE, and then
> mount the root filesystem over NFS.
> Then, to flash the devices before they go in production in the field, I
> would create a minimal Linux system,

Do you mean that I have the honor to use buildroot twice for one
device ?! :D once for the little network boot, and one operationnal.

> that you boot over the network
> using PXE, and this Linux system downloads and flash the real Linux
> system in the internal Flash of your system (which apparently is
> accessed as a normal ATA hard drive). You make sure this minimal Linux
> system makes all this process automatically when it is booted, so
> whenever you boot one of your system on a network that has your
> PXE/TFTP server on it, it will be erased and reflashed (of course, be
> careful not to boot a real laptop or desktop system in the same network
> segment, or it might boot over the network and get erased).
> Does this helps?

Yes ! It's a nice solution that I wouldn't have found alone. It'll
take me some time to manage all concepts behind this (I mean general
network boot). I really like the idea of auto reflash when the pxe
server is started.

I just have one robot, and he will be the only one to boot on PXE, so
it should be ok.

> For a simple PXE/TFTP server solution, I would strongly suggest using
> ptftpd/pxed: <https://ssl.bulix.org/svn/ptftpd/trunk/>. It is very
> simple to setup (just *one* command to have a complete PXE solution
> running).
>> For completness here is my board datasheet, but I don't expect anyone
>> to read :-). It's an Advantech PCM-3362
>> http://support.elmark.com.pl/advantech/pdf/pcm-3362man.pdf
> I actually read it, and verified that your board is capable of booting
> over the network, and it apparently is.

Yes. I have to check that my CAN stack doesn't conflict with memory/irq/...

>> Is it possible to use other filesystems, like ext3 or 4 ?
> Yes, you just need to do some tuning of your ext2 image using tune2fs.
> I really should submit a patch to add support for ext3 and ext4 image
> generation in Buildroot.

Yes please ! Among others, I would really love that.

> Best regards,
> Thomas
> --
> Thomas Petazzoni, Free Electrons
> Kernel, drivers, real-time and embedded Linux
> development, consulting, training and support.
> http://free-electrons.com

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