[Libguestfs] debug a corrupted VHDX file with libguestfs

Hi I am using libguestfs-1.46.2 on Ubuntu 22.04 I already enabled export LIBGUESTFS_DEBUG=1 export LIBGUESTFS_TRACE=1 I want to mount a vhdx file (which is known to be corrupted) with root@HenrikUbuntu2204:/mnt/sdj# guestmount -a c1eef115-00000006-ec888b8d-64888b8d-00155000-4a448456 -m /dev/sda1 --ro /mnt/sdk/ where I can see the following error message from output [ 46.629055] EXT4-fs (sda1): ext4_check_descriptors: Block bitmap for group 524288 not in group (block 0)! [ 46.629656] EXT4-fs (sda1): group descriptors corrupted! command: mount returned 32 I want to actually add debug logs into ext4_check_descriptors with printk To print out the hex values of superblock in the corrupted vhdx file I tried to recompile Ubuntu kernel and add some printk messages, they don't show up in dmesg when I run root@HenrikUbuntu2204:/mnt/sdj# guestmount -a c1eef115-00000006-ec888b8d-64888b8d-00155000-4a448456 -m /dev/sda1 --ro /mnt/sdk/ I guess the following messages are from libvirt / KVM ? [ 46.629055] EXT4-fs (sda1): ext4_check_descriptors: Block bitmap for group 524288 not in group (block 0)! [ 46.629656] EXT4-fs (sda1): group descriptors corrupted! How do I use printk to add logs in the kernel messages from libguestfs? Regards Henrik Internal Use - Confidential