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

[Martin Kletzander]

On Tue, Mar 04, 2014 at 06:44:01AM -0700, Eric Blake wrote:
> 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?
>

I haven't thought that through, just from top of my head:

#define SESSION_UNSUPP(what) if (!cfg->privileged) {              \
    virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s %s",           \
                   what, _("is not available in sesison mode"));  \
    goto cleanup;                                                 \
    }

because the code repeats a lot, but it seems like it would not be that
readable.  Separate function would do as well.

> >
> >      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.
>

I was just trying to output a better error message and forgot to add
the BZ that started it:

https://bugzilla.redhat.com/show_bug.cgi?id=1023366

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

Anyway, I'll have a second version which allows at least cpu pinning
as setaffinity works and is used when no cgroups are available.

Martin
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