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https://github.com/vincentbernat/eudyptula-boot

Boot a Linux kernel in a VM without a dedicated root filesystem.
https://github.com/vincentbernat/eudyptula-boot

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Boot a Linux kernel in a VM without a dedicated root filesystem.

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README 

        
eudyptula-boot

==============



`eudyptula-boot` boots a Linux kernel in a VM without a dedicated root

filesystem. The root filesystem is the underlying root filesystem (or

some pre-built chroot). This is a convenient way to do quick tests

with a custom kernel.



The name comes from [Eudyptula][] which is a genus for penguins. This

is also the name of a [challenge for the Linux kernel][].



This utility is aimed at development only. This is a hack. It relies

on AUFS/overlayfs and 9P to build the root filesystem from the running

system.



[Eudyptula]: http://en.wikipedia.org/wiki/Eudyptula

[challenge for the Linux kernel]: http://eudyptula-challenge.org/



Also see

[this blog post](http://vincent.bernat.ch/en/blog/2014-eudyptula-boot)

for a quick presentation of this tool.



Usage

-----



It is preferable to have a kernel with AUFS or OverlayFS

enabled. Ubuntu and Debian kernels are patched to support AUFS. Since

3.18, vanilla kernels have OverlayFS built-in. Ubuntu kernels also

come with OverlayFS support. Check you have one of those options:



    CONFIG_AUFS_FS=y

    CONFIG_OVERLAY_FS=y

    CONFIG_OVERLAYFS_FS=y



Ensure you have the following options enabled (as a module or builtin):



    CONFIG_9P_FS=y

    CONFIG_NET_9P=y

    CONFIG_NET_9P_VIRTIO=y

    CONFIG_VIRTIO=y

    CONFIG_VIRTIO_PCI=y

    CONFIG_VIRTIO_CONSOLE=y



To get a somewhat minimal configuration, have a look at the

`minimal-configuration` script.



Once compiled, the kernel needs to be installed in some work directory:



    $ make modules_install install INSTALL_MOD_PATH=$WORK INSTALL_PATH=$WORK



Then, boot your kernel with:



    $ eudyptula-boot --kernel $WORK/vmlinuz-3.15.0~rc5-02950-g7e61329b0c26



Use `--help` to get additional available options.



Before booting the kernel, the path to GDB socket will be

displayed. You can use it by running gdb on `vmlinux` (which is

somewhere in the source tree):



    $ gdb vmlinux

    GNU gdb (GDB) 7.4.1-debian

    Reading symbols from /home/bernat/src/linux/vmlinux...done.

    (gdb) target remote /path/to/vm-eudyptula-gdb.pipe

    Remote debugging using /path/to/vm-eudyptula-gdb.pipe

    native_safe_halt () at /home/bernat/src/linux/arch/x86/include/asm/irqflags.h:50

    50  }

    (gdb)



If you have modules, you also need to manually load debug symbols for

them. In guest:



    $ grep . /sys/module/vxlan/sections/{.text,.data,.bss}

    /sys/module/vxlan/sections/.text:0xffffffffc0370000

    /sys/module/vxlan/sections/.data:0xffffffffc0378000

    /sys/module/vxlan/sections/.bss:0xffffffffc0378900



In GDB:



    (gdb) add-symbol-file /usr/lib/debug/lib/modules/$(uname -r)/kernel/drivers/net/vxlan.ko \

                          0xffffffffc0370000 \

                 -s .data 0xffffffffc0378000 \

                 -s .bss  0xffffffffc0378900



This can be automated with `lx-symbols` command if you source

`vmlinux-gdb.py` from a compiled kernel.



A serial port is also exported. It can be convenient for remote

debugging of userland processes. More details can be found in this

[blog post][] (which also covers debugging the kernel).



[blog post]: http://vincent.bernat.ch/en/blog/2012-network-lab-kvm



QEMU monitor is also attached to a UNIX socket. You can use the

following command to interact with it:



    $ socat - UNIX:/path/to/vm-eudyptula-console.pipe

    QEMU 2.0.0 monitor - type 'help' for more information

    (qemu)



You can also get something similar to [guestfish][]:



    $ eudyptula-boot --qemu="-drive file=someimage.qcow2,media=disk,if=virtio"



With `--extra-gettys`, you can allocate additional consoles. To access

one of them, use:



    $ socat STDIO,echo=0,icanon=0 UNIX:/tmp/tmp.oCshB5ryj4/getty-1.pipe



[guestfish]: http://libguestfs.org/guestfish.1.html



Alternatives

------------



Similar projects exist:



 - https://github.com/g2p/vido

 - https://git.kernel.org/cgit/utils/kernel/virtme/virtme.git/