Re: [PATCH] mdev: Send uevents around parent device registration

Cornelia Huck
2019-07-01T08:10:26Z

On Thu, 27 Jun 2019 19:42:32 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> On 6/27/2019 1:51 PM, Cornelia Huck wrote:
> > On Thu, 27 Jun 2019 00:33:59 +0530
> > Kirti Wankhede <kwankhede@nvidia.com> wrote:
> >
> >> On 6/26/2019 11:35 PM, Alex Williamson wrote:
> >>> On Wed, 26 Jun 2019 23:23:00 +0530
> >>> Kirti Wankhede <kwankhede@nvidia.com> wrote:
> >>>
> >>>> On 6/26/2019 7:57 PM, Alex Williamson wrote:
> >>>>> This allows udev to trigger rules when a parent device is registered
> >>>>> or unregistered from mdev.
> >>>>>
> >>>>> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> >>>>> ---
> >>>>> drivers/vfio/mdev/mdev_core.c | 10 ++++++++--
> >>>>> 1 file changed, 8 insertions(+), 2 deletions(-)
> >>>>>
> >>>>> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> >>>>> index ae23151442cb..ecec2a3b13cb 100644
> >>>>> --- a/drivers/vfio/mdev/mdev_core.c
> >>>>> +++ b/drivers/vfio/mdev/mdev_core.c
> >>>>> @@ -146,6 +146,8 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops)
> >>>>> {
> >>>>> int ret;
> >>>>> struct mdev_parent *parent;
> >>>>> + char *env_string = "MDEV_STATE=registered";
> >>>>> + char *envp[] = { env_string, NULL };
> >>>>>
> >>>>> /* check for mandatory ops */
> >>>>> if (!ops || !ops->create || !ops->remove || !ops->supported_type_groups)
> >>>>> @@ -196,7 +198,8 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops)
> >>>>> list_add(&parent->next, &parent_list);
> >>>>> mutex_unlock(&parent_list_lock);
> >>>>>
> >>>>> - dev_info(dev, "MDEV: Registered\n");
> >>>>> + kobject_uevent_env(&dev->kobj, KOBJ_CHANGE, envp);
> >>>>> +
> >>>>
> >>>> Its good to have udev event, but don't remove debug print from dmesg.
> >>>> Same for unregister.
> >>>
> >>> Who consumes these? They seem noisy. Thanks,
> >>>
> >>
> >> I don't think its noisy, its more of logging purpose. This is seen in
> >> kernel log only when physical device is registered to mdev.
> >
> > Yes; but why do you want to log success? If you need to log it
> > somewhere, wouldn't a trace event be a much better choice?
> >
>
> Trace events are not always collected in production environment, there
> kernel log helps.

I'm with you for *errors*, but I'm not sure you should rely on
*success* messages, though. If you want to be able to figure out the
sequence of registering etc. in all cases, I think it makes more sense
to invest in an infrastructure like tracing and make sure that is it
turned on for any system that matters.