On Thu, Nov 8, 2018 at 2:05 PM Nathan Rossi <nat...@nathanrossi.com> wrote: > > On Wed, 7 Nov 2018 at 23:32, Andrea Adami <andrea.ad...@gmail.com> wrote: > > > > On Wed, Nov 7, 2018 at 1:16 PM Nathan Rossi <nat...@nathanrossi.com> wrote: > > > > > > The kernel has two differing code paths when handling a built-in cpio > > > versus a cpio passed to the kernel from a boot loader. When the kernel > > > is booted with the built-in cpio it expects the /dev/console node to > > > exist and will panic if it does not exist. > > > > > > Kernel panic - not syncing: /dev/console is missing or not a character > > > device! > > > > > > When the cpio is passed to the kernel via a bootloader, this behaviour > > > is not observed. > > > > > > > Well, of course once booted you have devtmpfs or you have provided > > your devices-list. > > We fight since long with this early issues and I think this approach > > is wrong: there are more things needed, not only /dev/consoleI'd say > > the responsability to check for devtmpfs or recreate the devices is up > > to init manager of the image. > > Ok, so I do not think my commit message was clear enough in this regard. > > Firstly the kernel requires the /dev/console node before the init > process is started, but after it has unpacked the built-in ramfs and > after it has mounted the initrd (rd or ramfs). You can see the exact > call that attempts to open /dev/console here: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/init/main.c?h=v4.20-rc1#n1154 > > The exact problem this change is solving is the fact that by embedding > a user source cpio into the kernel, the default kernel initramfs is > replaced. The default kernel ramfs contains /dev, /dev/console and > /root. > > Also for reference when the kernel is built without > initramfs/BLK_DEV_INITRD support it will create this default rootfs > with an alternate initcall: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/init/noinitramfs.c?h=v4.20-rc1 > > So essentially the kernel is always expecting the rootfs to contain > this /dev/console node. > > > > > We don't use busybox, just a single binary running as init: kexecboot > > will exactly do that, check and recreate devices if missing: > > http://cgit.openembedded.org/meta-openembedded/tree/meta-initramfs/recipes-bsp/kexecboot/kexecboot_git.bb > > This only solves the user space requirements for device nodes. Since > kexecboot or busybox will not be executed before the kernel tries to > open the /dev/console file. > Rightm and nothing bad will happen, just the pr_err("Warning: unable to open an initial console.\n");
then init is run. > > > > Please don't inject anything in the cpio, let the image-engineer decide. > > > > This poor image is regularly attacked by new changes filling the cpio > > with undesidered stuff: > > http://cgit.openembedded.org/meta-openembedded/tree/meta-initramfs/recipes-bsp/images/initramfs-kexecboot-image.bb > > How does this image handle this /dev/console dependency? Is there > something I am missing with how it is built into the kernel, or with > how the kernel you are using is configured? > > It appears the initramfs-framework images of oe-core solve this by > creating the node in the image itself. > http://git.openembedded.org/openembedded-core/tree/meta/recipes-core/initrdscripts/initramfs-framework_1.0.bb#n51 > http://git.openembedded.org/openembedded-core/tree/meta/recipes-core/initrdscripts/initramfs-live-boot_1.0.bb#n15 > http://git.openembedded.org/openembedded-core/tree/meta/recipes-core/initrdscripts/initramfs-live-boot-tiny_1.0.bb > > Looking at the log of those files, it appears this might have been a > kernel version and/or architecture specific thing back in 2013... > http://git.openembedded.org/openembedded-core/commit/?id=0352841cd92f6316bcac092e2fff9d28c352b36b > > > And I had to revert it... http://cgit.openembedded.org/meta-openembedded/commit/meta-initramfs/recipes-kernel?id=7183bacd5c866d433467a750e485e6c01af4aafc > > Maybe we are on the corner-case, size-contraints limit us to be within > > 1MiB, neverthless I think it is a good exercise to keep things small > > and clean ;) > > I would also like to avoid this change if there is an alternative that > works better. > Well, at the beginning we used IMAGE_DEVICE_TABLES to populate it. Then whit the introduction of devtmpfs (3.2 iirc) we switched using it, to save the few kb of the /dev:the trick here is that devtmpfs automount does not work in the initramfs so you have to mount devtmpfs by hand in your init, like here https://github.com/kexecboot/kexecboot/blob/master/src/kexecboot.c#L734 Cheers Andrea > Thanks, > Nathan > > > > > As for the previous patch touching initramfs, I hold my comments for > > the moment: let me first test it. > > Cheers > > > > Andrea > > > > > To resolve this issue, ensure any cpio that is built into the kernel is > > > prepared with a /dev/console node. This is done by appending to the > > > copied cpio of the INITRAMFS_IMAGE. In order to create the node to > > > append, the task must be executed with root permission (to run mknod). > > > As such this change creates and intermediate _prepare task between the > > > existing _bundle and _copy tasks. > > > > > > Note: The default/minimal initramfs that the kernel sources > > > gen_initramfs_list.sh generates contains this device node. > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/usr/gen_initramfs_list.sh?h=master#n55 > > > > > > Signed-off-by: Nathan Rossi <nat...@nathanrossi.com> > > > --- > > > meta/classes/kernel-initramfs.bbclass | 15 ++++++++++++++- > > > 1 file changed, 14 insertions(+), 1 deletion(-) > > > > > > diff --git a/meta/classes/kernel-initramfs.bbclass > > > b/meta/classes/kernel-initramfs.bbclass > > > index b23fb51495..135f4c8949 100644 > > > --- a/meta/classes/kernel-initramfs.bbclass > > > +++ b/meta/classes/kernel-initramfs.bbclass > > > @@ -16,7 +16,8 @@ python __anonymous () { > > > if image and bundle: > > > # add all the tasks > > > bb.build.addtask('do_initramfs_copy', 'do_initramfs_bundle', > > > 'do_install', d) > > > - bb.build.addtask('do_initramfs_bundle', 'do_deploy', > > > 'do_initramfs_copy', d) > > > + bb.build.addtask('do_initramfs_prepare', 'do_initramfs_bundle', > > > 'do_initramfs_copy', d) > > > + bb.build.addtask('do_initramfs_bundle', 'do_deploy', > > > 'do_initramfs_prepare', d) > > > > > > # make the do_initramfs_copy task depend on the image > > > do_image_complete task > > > d.appendVarFlag('do_initramfs_copy', 'depends', ' > > > ${INITRAMFS_IMAGE}:do_image_complete') > > > @@ -67,6 +68,18 @@ do_initramfs_copy () { > > > echo "Finished copy of initramfs into ./usr" > > > } > > > > > > +do_initramfs_prepare[dirs] = "${B}" > > > +fakeroot do_initramfs_prepare () { > > > + echo "Preparing initramfs by creating required /dev/ nodes" > > > + # append a /dev/console node, this node must be created in the rootfs > > > + # for built-in initramfs cpios otherwise it will error with: > > > + # Kernel panic - not syncing: /dev/console is missing or not a > > > character device! > > > + rm -rf ${B}/usr/append > > > + mkdir -p ${B}/usr/append/dev > > > + mknod -m 600 ${B}/usr/append/dev/console c 5 1 > > > + (cd ${B}/usr/append && echo "./dev/console" | cpio -oA -H newc -F > > > ${B}/usr/${INITRAMFS_IMAGE_NAME}.cpio) > > > +} > > > + > > > do_initramfs_bundle[dirs] = "${B}" > > > do_initramfs_bundle () { > > > echo "Creating a kernel image with a bundled initramfs..." > > > --- > > > 2.19.1 > > > -- > > > _______________________________________________ > > > Openembedded-core mailing list > > > Openembedded-core@lists.openembedded.org > > > http://lists.openembedded.org/mailman/listinfo/openembedded-core -- _______________________________________________ Openembedded-core mailing list Openembedded-core@lists.openembedded.org http://lists.openembedded.org/mailman/listinfo/openembedded-core
