Arch Linux

djrollins

Member

From: Leeds, UK

Registered: 2016-07-11

Posts: 6

Website

Custom kernel won't boot on btrfs. Cannot open /dev/btrfs-control.

Hi all,

I'm working on a series of challenges and one of them is to compile the latest kernel revision and boot into it.

I've gone through this successfully a number of times before but for some reason I cannot boot into the new kernel because btrfs fails with an error and I get dumped into a root shell.

My usual process is the following:

$ git pull                                  # update to tip of master
$ make clean && make mrproper               # completely clean repository for new build
$ make localmodconfig                       # use current config as a base and accept defaults for new configs
$ vim .config                               # enable CONFIG_LOCALVERSION_AUTO
$ make -j8
$ sudo make modules_install
$ cp /etc/mkinitcpio.conf ~/mkinicpio.conf
$ vim ~/mkinicpio.conf                      # remove nvidia junk from MODULES
$ sudo cp arch/x86_64/boot/bzImage /boot/vmlinuz-custom
$ sudo mkinitcpio -k /boot/vmlinuz-custom -g /boot/initramfs-custom.img -c ~/mkinicpio.conf
$ sudo grub-mkconfig -o /boot/grub/grub.cfg

On boot, when trying to find btrfs filesystems, I get an error saying /dev/btrfs-control cannot be opened.

From the root shell, I can see the /dev/btrfs-control node, so it does exist.

Any ideas what is causing this problem or if there are any steps I'm forgetting about?

Many thanks,

Daniel

EDITS:
- I have tried compiling v4.10 (same as my main installation) and have the same issue there which suggests it's not a newly introduced bug.
- I can boot into my main installation fine, this is purely an issue with my the custom kernel.

Last edited by djrollins (2017-03-29 20:56:35)

loqs

Member

Registered: 2014-03-06

Posts: 18,961

Re: Custom kernel won't boot on btrfs. Cannot open /dev/btrfs-control.

please post the config for the custom kernel.
Edit:
Also the dmesg from the failed boot.

Last edited by loqs (2017-03-29 21:31:10)

djrollins

Member

From: Leeds, UK

Registered: 2016-07-11

Posts: 6

Website

Re: Custom kernel won't boot on btrfs. Cannot open /dev/btrfs-control.

Hi loqs,

Sorry for the delayed response.

I recompiled the kernel using the config straight from /proc/config.gz and everything compiled and booted correctly. It seems to be that the btrfs module is not loading on boot if I compile with a config from localmodconfig.

The working config (/proc/config.gz)  is here
The broken config (make localmodconfig)  is here

As for the dmesg output, I do not have network capabilities in my initramfs, so couldn't export the whole thing. I did take a picture, if that suffices.

link

It shows that nothing is added to the dmesg output when I try to modprobe btrfs.