[libvirt] [RFC PATCH] lxc: don't return error on GetInfo when cgroups not yet set up

Daniel P. Berrange berrange at redhat.com
Thu Sep 29 08:38:45 UTC 2011

On Wed, Sep 28, 2011 at 02:14:52PM -0500, Serge E. Hallyn wrote:
> Nova (openstack) calls libvirt to create a container, then
> periodically checks using GetInfo to see whether the container
> is up.  If it does this too quickly, then libvirt returns an
> error, which in libvirt.py causes an exception to be raised,
> the same type as if the container was bad.

lxcDomainGetInfo(), holds a mutex on 'dom' for the duration of
its execution. It checks for virDomainObjIsActive() before
trying to use the cgroups.

lxcDomainStart(), holds the mutex on 'dom' for the duration of
its execution, and does not return until the container is running
and cgroups are present.

Similarly when we delete the cgroups, we again hold the lock
on 'dom'.

Thus any time viDomainObjIsActive() returns true, AFAICT, we have
guaranteed that the cgroup does in fact exist.

So can't see how control gets to the 'else' part of this
condition if the cgroups don't exist like you describe.

    if (!virDomainObjIsActive(vm) || driver->cgroup == NULL) {
        info->cpuTime = 0;
        info->memory = vm->def->mem.cur_balloon;
    } else {
        if (virCgroupForDomain(driver->cgroup, vm->def->name, &cgroup, 0) != 0) {
                     _("Unable to get cgroup for %s"), vm->def->name);
            goto cleanup;

What libvirt version were you seeing this behaviour with ?

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