[libvirt] [PATCH 2/2] qemu: Reject unsupported tuning in session mode

[Eric Blake]

On 03/03/2014 10:21 AM, Martin Kletzander wrote:
> When domain is started with setting that cannot be done, i.e. those
> that require cgroups, there is no error reported and it succeeds
> without any message whatsoever.
> 
> When setting with API, virsh, an error is reported, but only due to
> the fact that no cgroups are mounted (priv->cgroup == NULL).
> 
> Given the above it seems reasonable to reject such unsupported
> settings.
> 
> Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
> ---
> 
> Notes:
>     Few questions came to my mind while writing the commit message:
>     
>      1) Would helper function (macro) be preferred so the code looks
>         cleaner?

What macro do you have in mind?

>     
>      2) Do we want to allow reading of some of these settings through an
>         API?  This would however require our cgroup handling to be
>         reworked.
>     
>      3) Would new error type (for session-unsupported settings) be any
>         good or it doesn't make sense to create one just for these added
>         messages plus few older ones (just guessing the amount)?

Looks like your use of VIR_ERR_CONFIG_UNSUPPORTED was reasonable.

> +    if (!cfg->privileged) {
> +        /* If we have no cgroups than we can have no tunings that
> +         * require them */
> +
> +        if (def->mem.hard_limit || def->mem.soft_limit ||
> +            def->mem.min_guarantee || def->mem.swap_hard_limit) {
> +            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> +                           _("Memory tuning is not available in session mode"));
> +            goto error;
> +        }
> +

Or maybe we should think about some day adding a daemon that accepts RPC
commands for manipulating cgroups on behalf of a session client.  But
that would be a later and bigger patch.

Seems reasonable to me, but it might be nice to also get Dan's opinion
on this one.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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