On Fri, Mar 05, 2021 at 09:45:41AM +0100, Bartosz Golaszewski wrote:
> On Fri, Mar 5, 2021 at 9:34 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > On Fri, Mar 05, 2021 at 09:18:30AM +0100, Geert Uytterhoeven wrote:
> > > CC Greg
> > >
> > > On Thu, Mar 4, 2021 at 11:30 AM Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
> > > >
> > > > From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> > > >
> > > > Export the symbol for device_is_bound() so that we can use it in gpio-sim
> > > > to check if the simulated GPIO chip is bound before fetching its driver
> > > > data from configfs callbacks in order to retrieve the name of the GPIO
> > > > chip device.
> > > >
> > > > Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> > > > ---
> > > > drivers/base/dd.c | 1 +
> > > > 1 file changed, 1 insertion(+)
> > > >
> > > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> > > > index 9179825ff646..c62c02e3490a 100644
> > > > --- a/drivers/base/dd.c
> > > > +++ b/drivers/base/dd.c
> > > > @@ -353,6 +353,7 @@ bool device_is_bound(struct device *dev)
> > > > {
> > > > return dev->p && klist_node_attached(&dev->p->knode_driver);
> > > > }
> > > > +EXPORT_SYMBOL_GPL(device_is_bound);
> >
> > No. Please no. Why is this needed? Feels like someone is doing
> > something really wrong...
> >
> > NACK.
> >
>
> I should have Cc'ed you the entire series, my bad.
>
> This is the patch that uses this change - it's a new, improved testing
> module for GPIO using configfs & sysfs as you (I think) suggested a
> while ago:
>
> https://lkml.org/lkml/2021/3/4/355
>
> The story goes like this: committing the configfs item registers a
> platform device.
Ick, no, stop there, that's not a "real" device, please do not abuse
platform devices like that, you all know I hate this :(
Use the virtbus code instead perhaps?
> As far as I understand - there's no guarantee that
> the device will be bound to a driver before the commit callback (or
> more specifically platform_device_register_full() in this case)
> returns so the user may try to retrieve the name of the device
> immediately (normally user-space should wait for the associated uevent
> but nobody can force that) by doing:
>
> mv /sys/kernel/config/gpio-sim/pending/foo /sys/kernel/config/gpio-sim/live/
> cat /sys/kernel/config/gpio-sim/live/foo/dev_name
>
> If the device is not bound at this point, we'll have a crash in the
> kernel as opposed to just returning -ENODEV.
How will the kernel crash? What has created the dev_name sysfs file
before it is possible to be read from? That feels like the root
problem.
> Please advise on how to handle it without device_is_bound().
Please do not create sysfs files before they can be read from :)
thanks,
greg k-h
