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1. Bernie (codewiz@mstdn.io)'s status on Sunday, 19-Dec-2021 08:03:24 UTC Bernie

   Anyone knows how to setup kvm/libvirt to boot a VM directly from an LVM partition containing a filesystem?

   I just want the host to load the latest kernel + initrd from the root filesystem of the VM without the need for a DOS partition table, an MBR to load GRUB, etc.

   • Bernie (codewiz@mstdn.io)'s status on Sunday, 19-Dec-2021 08:06:32 UTC Bernie

     in reply to

     • Stanislas :NotLikeThis:
     • Benoit

     And if the solution starts with "create a GPT and a UEFI boot partition", then I'm happy to keep the MBR.

     What I'm looking for is to simplify VM disks down to a plain filesystem hosted in an LVM logical volume. Now I have this DOS/GPT disk nonsense that can't be mounted on the host without special magic.

     cc: @benoit @angristan

   • スプリットショックウイルス :arch_linux: (splitshockvirus@distrotoot.com)'s status on Sunday, 19-Dec-2021 09:25:00 UTC スプリットショックウイルス :arch_linux:

     in reply to

     @codewiz I think libvirt manager has xml support for filesystems as a way to attach disk storage.

     I don't know if it can be used to accomplish what you described (as in I've never done that). However there is the ability to mount qcow2 disks directly onto a linux filesystem via qemu-nbd so I don't see why what you described wouldn't be possible.

     I'll look into this later today if you haven't found out an answer.

   • Bernie (codewiz@mstdn.io)'s status on Sunday, 19-Dec-2021 09:25:00 UTC Bernie

     in reply to

     • スプリットショックウイルス :arch_linux:

     @SplitShockVirus Thank you!

   • Bernie (codewiz@mstdn.io)'s status on Sunday, 19-Dec-2021 09:35:01 UTC Bernie

     in reply to

     • Patrick Georgi

     @patrick I like the qemu + coreboot with a grub payload idea because it should work seamlessly with any distro which updates the grub config after installing a kernel update.

     Where do I find the right image? Or how would I build it myself?

   • Patrick Georgi (patrick@georgi.family)'s status on Sunday, 19-Dec-2021 09:35:03 UTC Patrick Georgi

     in reply to
     @codewiz mount -oro,loop your-lvm-partition /somewhere; cp /somewhere/bzImage /somewhere/initrd /tmp/foo; umount /somewhere; kvm -kernel /tmp/foo/kernel -initrd /tmp/foo/initrd -all -the -other -kvm -cruft
     
     ;-)
     
     The more sophisticated variant (that gets by without the host kernel touching VM data, which can be awkward if the VM kernel messed with it in unknown ways) would be an emulation/qemu-q35 coreboot image with grub2 or filo or something as payload. That way the in-"flash" code knows your filesystem and can load kernels directly.
     
     The option for enable such an image in kvm would be "kvm -bios /path/to/bios/image", and I guess libvirt has some underexercised config field doing the same.