Creating a filesystem for QEMU

I am trying to use QEMU for development of embedded systems using Real
Time Linux. Buildroot seems to be the tool I need, but I still don't know how
to build a disk image recognized by QEMU. Right now I am trying to use only x86 and x86_64 architectures.
Does anyone know how to build a file system usable in QEMU ?
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- You can generate a cloop root filesystem using buildroot, and then convert it to the format you want using qemu-img
- Create an initramfs, and boot it using qemu
- Create an ext2 filesystem and write it on a qemu disk through an install cdrom
- and so on....

Quoted 7 lines · On Thursday 12 November 2009 16:58:15 you wrote:

- You can generate a cloop root filesystem using buildroot, and then convert it to the format you want using qemu-img
- Create an initramfs, and boot it using qemu
- Create an ext2 filesystem and write it on a qemu disk through an install cdrom
- and so on....

Thank you for your feedback, I'll try to explore these options in the
next
days. IMHO it could be extremely useful to have these indications into the help page of buildroot.
Could you expand a little more the last option (Create an ext2 filesystem
and write it on a qemu disk through an install cdrom). I don't understand that
part.

thanks
Bogdan

Thank you for your feedback, I'll try to explore these options in the next
days. IMHO it could be extremely useful to have these indications into the help page of buildroot.
Could you expand a little more the last option (Create an ext2 filesystem
and write it on a qemu disk through an install cdrom). I don't understand that part.

qemu-img create qemu.img 4G
mount -o loop,offset=32256 qemu.img /mnt

? ?I am trying to use QEMU for development of embedded systems using Real Time Linux. Buildroot seems to be the tool I need, but I still don't know how to build a disk image recognized by QEMU. Right now I am trying to use only x86 and x86_64 architectures.
? ?Does anyone know how to build a file system usable in QEMU ?
_______________________________________________
buildroot mailing list
buildroot at busybox.net
http://lists.busybox.net/mailman/listinfo/buildroot

I've just started doing the same thing myself. After a bit of googling the trick I found was to ask buildroot to generate a cpio target file system. Start with the i386_defconfig or i686_defconfig and set BR2_TARGET_ROOTFS_CPIO=y (or use "make menuconfig" an find the cpio option under the "Target file system" menu)

Making use of qemus ability to replace the bootloader you can invoke qemu with

    qemu -kernel output/images/bzImage \
         -initrd output/images/rootfs.i686.cpio

Quoted 6 lines · On Thursday 12 November 2009 16:46:32 you wrote:

I've just started doing the same thing myself. After a bit of googling the trick I found was to ask buildroot to generate a cpio target file system. Start with the i386_defconfig or i686_defconfig and set BR2_TARGET_ROOTFS_CPIO=y (or use "make menuconfig" an find the cpio option under the "Target file system" menu)

Quoted 4 lines

Making use of qemus ability to replace the bootloader you can invoke qemu with

    qemu -kernel output/images/bzImage \
         -initrd output/images/rootfs.i686.cpio

Quoted 1 line

I have tried this approach, but it does not seem to work. First
inconvenient is that rootfs.i686.cpio file is very large (600 MB) and when using the above command I only get a black screen from QEMU while the entire
computer seems to be slower.
Lionel, suggested other approaches but till now I have no luck. Trying
to
obtain first a cloop root filesystem and then convert that to a QEMU format seem to work and the file size is small (3 MB), but still when using that disk
image, QEMU is not able to recognize any root partition.
If you have any other suggestion it would be helpful.
_______________________________________________
buildroot mailing list
buildroot at busybox.net
http://lists.busybox.net/mailman/listinfo/buildroot

Quoted 7 lines · Bogdan Cristea

Quoted 6 lines · On Thursday 12 November 2009 16:46:32 you wrote:

I've just started doing the same thing myself. After a bit of googling the trick I found was to ask buildroot to generate a cpio target file system. Start with the i386_defconfig or i686_defconfig and set BR2_TARGET_ROOTFS_CPIO=y (or use "make menuconfig" an find the cpio option under the "Target file system" menu)

Quoted 5 lines

Quoted 4 lines

Making use of qemus ability to replace the bootloader you can invoke qemu with

    qemu -kernel output/images/bzImage \
         -initrd output/images/rootfs.i686.cpio

Shouldn't be the cpio image gunzipped ? :

$ file /boot/initrd.img-2.6.30-2-686
/boot/initrd.img-2.6.30-2-686: gzip compressed data, from Unix, last
modified: Fri Nov 13 09:08:02 2009
$ gunzip -c /boot/initrd.img-2.6.30-2-686 > test
$ file test
test: ASCII cpio archive (SVR4 with no CRC)

Quoted 19 lines

Quoted 1 line

I have tried this approach, but it does not seem to work. First
inconvenient is that rootfs.i686.cpio file is very large (600 MB) and when using the above command I only get a black screen from QEMU while the entire
computer seems to be slower.
Lionel, suggested other approaches but till now I have no luck. Trying
to
obtain first a cloop root filesystem and then convert that to a QEMU format
seem to work and the file size is small (3 MB), but still when using that disk
image, QEMU is not able to recognize any root partition.
If you have any other suggestion it would be helpful.
_______________________________________________
buildroot mailing list
buildroot at busybox.net
http://lists.busybox.net/mailman/listinfo/buildroot

Quoted 6 lines

Quoted 4 lines

Quoted 4 lines

Making use of qemus ability to replace the bootloader you can invoke qemu with
? ? qemu -kernel output/images/bzImage \
? ? ? ? ?-initrd output/images/rootfs.i686.cpio

Shouldn't be the cpio image gunzipped ? :

I mean gzipped of course...

Quoted 5 lines · Lionel Landwerlin

Quoted 5 lines

Quoted 4 lines

Quoted 4 lines

Making use of qemus ability to replace the bootloader you can invoke qemu with

    qemu -kernel output/images/bzImage \
         -initrd output/images/rootfs.i686.cpio

Quoted 3 lines

Quoted 1 line

Shouldn't be the cpio image gunzipped ? :

I mean gzipped of course...

Unzipped works for me. The cpio target makes 2 files. rootfs.ARCH.cpio and rootfs.ARCH.cpio.gz.
I just tried the .gz file and that works too.

Quoted 12 lines · Bogdan Cristea

Quoted 10 lines · On Thursday 12 November 2009 16:46:32 you wrote:

I've just started doing the same thing myself. After a bit of googling the trick I found was to ask buildroot to generate a cpio target file system. Start with the i386_defconfig or i686_defconfig and set BR2_TARGET_ROOTFS_CPIO=y (or use "make menuconfig" an find the cpio option under the "Target file system" menu)

Making use of qemus ability to replace the bootloader you can invoke qemu with

    qemu -kernel output/images/bzImage \
         -initrd output/images/rootfs.i686.cpio

Quoted 9 lines

I have tried this approach, but it does not seem to work. First
inconvenient is that rootfs.i686.cpio file is very large (600 MB) and when using the above command I only get a black screen from QEMU while the entire computer seems to be slower.
Lionel, suggested other approaches but till now I have no luck. Trying
to obtain first a cloop root filesystem and then convert that to a QEMU format seem to work and the file size is small (3 MB), but still when using that disk image, QEMU is not able to recognize any root partition.
If you have any other suggestion it would be helpful.

I'd double check your configuration. I must admit I started hacking away without looking at the i686_defconfig. But I've got a rootfs thats only 3M and a kernel thats just under 4M. I've attached my buildroot config (.config) and kernel config (i386_defconfig) for your reference.

Also when you are hacking away re-configuring buildroot doesn't know to remove something up if you've de-selected it so you may need to manually clean out output/target/ manually (or start from fresh each time).

when using your .config file my compilation fails due to a missing patch file mpfr-2.4.1.patch. What is the role of that patch ?

Quoted 2 lines · Bogdan Cristea

when using your .config file my compilation fails due to a missing patch file mpfr-2.4.1.patch. What is the role of that patch ?

mpfr is used when generating gcc with floating point support. Its not something I've added locally.

My buildroot repository is based off the commit id 5e5f3209f which has got numerous changes since the 2009.08 release (including some in mpfr). If you do want to persue using my config you may want to get fresh git clone and seek to the same point as me. i.e.

git clone http://git.buildroot.net/buildroot
cd buildroot
git checkout -b test 5e5f3209f

Failing that maybe you just want to compare your config to mine and see if you have a bunch of extra packages that are causing your target file system to be so big.