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

Alex Williamson
2019-06-28T15:56:14Z

On Thu, 27 Jun 2019 10:19:14 +0200
Cornelia Huck <cohuck@redhat.com> wrote:

> On Wed, 26 Jun 2019 08:27:58 -0600
> Alex Williamson <alex.williamson@redhat.com> 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";
>
> This string is probably reasonable enough.
>
> > + 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);
>
> I also agree with the positioning here.
>
> > +
> > return 0;
> >
> > add_dev_err:
> > @@ -220,6 +223,8 @@ EXPORT_SYMBOL(mdev_register_device);
> > void mdev_unregister_device(struct device *dev)
> > {
> > struct mdev_parent *parent;
> > + char *env_string = "MDEV_STATE=unregistered";
>
> Ok.
>
> > + char *envp[] = { env_string, NULL };
> >
> > mutex_lock(&parent_list_lock);
> > parent = __find_parent_device(dev);
> > @@ -228,7 +233,6 @@ void mdev_unregister_device(struct device *dev)
> > mutex_unlock(&parent_list_lock);
> > return;
> > }
> > - dev_info(dev, "MDEV: Unregistering\n");
> >
> > list_del(&parent->next);
> > mutex_unlock(&parent_list_lock);
> > @@ -243,6 +247,8 @@ void mdev_unregister_device(struct device *dev)
> > up_write(&parent->unreg_sem);
> >
> > mdev_put_parent(parent);
> > +
> > + kobject_uevent_env(&dev->kobj, KOBJ_CHANGE, envp);
>
> I'm wondering whether we should indicate this uevent earlier: Once we
> have detached from the parent list, we're basically done for all
> practical purposes. So maybe move this right before we grab the
> unreg_sem?

That would make it a "this thing is about to go away" (ie.
"unregistering") rather than "this thing is gone" ("unregistered"). I
was aiming for the latter as the former just seems like it might make
userspace race to remove devices. Note that I don't actually make use
of this event in mdevctl currently, so we could maybe save it for
later, but the symmetry seemed preferable. Thanks,

Alex