There is a bug in qemu-guest-agent: $ virsh -c qemu:///system domfstrim gentoo-builder error: Unable to invoke fstrim error: internal error: unable to execute QEMU agent command «guest-fstrim»: failed to trim /home: Invalid argument This bug is reproducible with stable -2.1.2 and unstable -2.3.0. More details in the following commit: http://git.qemu-project.org/?p=qemu.git;a=patch;h=73a652a1b08445e8d91e50cdbb2da50e571c61b3 I've tested this patch with qemu-guest-agent-2.3.0. It fixes the issue: $ virsh -c qemu:///system domfstrim gentoo-builder $ echo $? 0
the 2.4.0 release should be soon since they've already started the rc's, so probably just wait for that and be lazy
2.4.0 is in the tree now