lxc container startup error and RFC patch

[Cole Robinson]

Hi all,

I'm seeing LXC container startup failures. This is with libvirt git,
fedora 34 host with systemd-248.6-1.fc34.x86_64 (I didn't confirm with
other versions). Reproducer:

sudo virt-install --connect lxc:/// --name test-container --memory 128 
--boot init=/bin/sh

Starting install...
ERROR    error from service: 
GDBus.Error:org.freedesktop.machine1.NoMachineForPID: PID 2145047 does 
not belong to any known machine

libvirt 7.0.0 works but 7.1.0+ does not. The root error seems to predate 
that, showing up in syslog, but commit 9c1693eff made it fatal:

commit 9c1693eff427661616ce1bd2795688f87288a412
Author: Pavel Hrdina <phrdina at redhat.com>
Date:   Fri Feb 5 16:17:35 2021 +0100

    vircgroup: use DBus call to systemd for some APIs

The error comes from virSystemdGetMachineByPID. The PID that shows up in 
the above error message does not match the leader PID as reported by 
machinectl. This change fixes the error but I don't know if it's correct 
or if it has other implications:

diff --git a/src/lxc/lxc_controller.c b/src/lxc/lxc_controller.c
index 066e013ed4..54ecb1316b 100644
--- a/src/lxc/lxc_controller.c
+++ b/src/lxc/lxc_controller.c
@@ -866,12 +866,12 @@ static int virLXCControllerSetupCgroupLimits(virLXCController *ctrl)
     nodeset = virDomainNumatuneGetNodeset(ctrl->def->numa, auto_nodeset, -1);
 
     if (!(ctrl->cgroup = virLXCCgroupCreate(ctrl->def,
-                                            ctrl->initpid,
+                                            getpid(),
                                             ctrl->nnicindexes,
                                             ctrl->nicindexes)))
         goto cleanup;
 
-    if (virCgroupAddMachineProcess(ctrl->cgroup, getpid()) < 0)
+    if (virCgroupAddMachineProcess(ctrl->cgroup, ctrl->initpid) < 0)
         goto cleanup;
 
     /* Add all qemu-nbd tasks to the cgroup */


Maybe something else isn't working elsewhere. Clearly we try to add both
pids to the systemd machine, but virSystemdGetMachineByPID is not
working to match the non-leader pid, which is the one that the LXC
driver knows about.

Thoughts?
Can anyone else reproduce?

Thanks,
Cole