[OE-core] qemu + initramfs

[Patrick Ohly]

On Mon, 2015-08-24 at 13:50 +0200, Patrick Ohly wrote:
> However, that failed initially with:
[...]
>         Kernel Offset: 0x0 from 0xc1000000 (relocation range: 0xc0000000-0xd07dffff)
>         ---[ end Kernel panic - not syncing: /dev/console is missing or not a character device!
>         Please ensure your rootfs is properly configured
> 
> Searching for the kernel panic led me to:
> http://stackoverflow.com/questions/10437995/initramfs-built-into-custom-linux-kernel-is-not-running
> 
> The hint given there (/dev/console must exist in the initramfs because
> the kernel opens it before executing /init) worked for like this:
> 
> diff --git a/meta/recipes-core/initrdscripts/initramfs-live-boot_1.0.bb
> b/meta/recipes-core/initrdscripts/initramfs-live-boot_1.0.bb
> index b54cb61..4066beb 100644
> --- a/meta/recipes-core/initrdscripts/initramfs-live-boot_1.0.bb
> +++ b/meta/recipes-core/initrdscripts/initramfs-live-boot_1.0.bb
> @@ -11,9 +11,12 @@ S = "${WORKDIR}"
>  
>  do_install() {
>          install -m 0755 ${WORKDIR}/init-live.sh ${D}/init
> +        install -d ${D}/dev
> +        mknod -m 622 ${D}/dev/console c 5 1
> +        mknod -m 622 ${D}/dev/tty0 c 4 0
>  }
>  
> -FILES_${PN} += " /init "
> +FILES_${PN} += " /init /dev "
>  
>  # Due to kernel dependency
>  PACKAGE_ARCH = "${MACHINE_ARCH}"
> 
> But I am surprised that I had to make such an adjustment. Isn't that
> something that also occurs in other build configurations? Do I perhaps
> miss something which avoids the issue (some kernel configuration
> perhaps)?

This is getting weirder. I checked MACHINE=intel-corei7-64 from
meta-intel with a regular live image (i.e. without my fix above). Some
additional ls debugging commands at the top of the init script show
that /dev/console exists, with a time that changes during each boot.
There's also /dev/0 -> /dev/console and similar entries for 1 and 2.

I know that /dev/ is from the rootfs (i.e. no tmpfs mounted on top of
it) because I still see a fake /dev/rootfs-dev file that I created in
the core-image-minimal-initramfs.

It almost looks like an overlay created or modified file system by the
kernel (because it's there before /init does anything), but I have no
idea what feature might responsible for that. Any hints?

-- 
Best Regards, Patrick Ohly

The content of this message is my personal opinion only and although
I am an employee of Intel, the statements I make here in no way
represent Intel's position on the issue, nor am I authorized to speak
on behalf of Intel on this matter.