I discovered that when a VM has an ISO attached via CD-ROM, libguestfs fails to read its partition table and therefore fails to perform basic operations on a VM, e.g. listing a directory or editing a file:
# virsh domblklist rocky9-vm Target Source --------------------------------------------------------------------------- sda /vz/vmprivate/e827caad-b9e4-4858-b3dc-53ae6b8a5145/harddisk.hdd sdb /vzt/images/Rocky-9.3-x86_64-minimal.iso # virt-ls -d rocky9-vm / libguestfs: error: inspect_os: sgdisk: Invalid partition data! # virt-edit -d rocky9-vm /etc/fstab libguestfs: error: inspect_os: sgdisk: Invalid partition data! Even virt-inspector can't give us proper output on an ISO9660 image: # virt-inspector /vzt/images/Rocky-9.3-x86_64-minimal.iso libguestfs: error: inspect_os: sgdisk: Invalid partition data! virt-inspector: no operating system could be detected inside this disk image. ... First I found a 3 years old topic where you suggested that sgdisk itself might be too old: https://listman.redhat.com/archives/libguestfs/2021-March/025939.html. However this doesn't seem to be it in this case: I've compiled the latest version from https://sourceforge.net/projects/gptfdisk -- no luck as well. Seems that sgdisk isn't capable of recognizing ISO9660 images. Then I noticed 2 things: 1. libguestfs appliance is being created (with backend=libvirt) with ISO attached as device='disk' (not 'cdrom'): > <disk type='file' device='disk'> > > <driver name='qemu' type='qcow2' cache='unsafe'/> > > <source file='/tmp/libguestfsD7IHvF/overlay2.qcow2' index='2'/> > > <backingStore type='file' index='5'> > > <format type='raw'/> > > > <source file='/vzt/images/Rocky-9.3-x86_64-minimal.iso'/> > > <backingStore/> > > </backingStore> > > <target dev='sdb' bus='scsi'/> > > <alias name='scsi0-0-1-0'/> > > <address type='drive' controller='0' bus='0' target='1' unit='0'/> > > </disk> That forces this disk to be supplied with "scsi-hd" driver in use, which in turn leads to the device being visible inside the guest as a regular SCSI hdd /dev/sdb. Shouldn't we, for instance, make sure that for such images device='cdrom' and "scsi-cd" driver are being used? In this case the guest will see it as /dev/sr0, and I suspect srX devices are being skipped by guestfs_inspect_os. 2. When trying to perform the same operation via guestfish, everything appears to be working: # guestfish -a /vzt/images/Rocky-9.3-x86_64-minimal.iso -m /dev/sda ls / >/dev/null && echo $? 0 File edit works as well. From debug output I see that sgdisk isn't being invoked at all. That means there's a code path for the same operations where sgdisk can be omitted. Maybe we should follow that same code path when invoking other tools like virt-ls or virt-edit? Overall, what would be an appropriate fix in your opinion? We should at least make sure that working with domains (with the "-d" option) works no matter what. Andrey _______________________________________________ Libguestfs mailing list -- guestfs@lists.libguestfs.org To unsubscribe send an email to guestfs-le...@lists.libguestfs.org
