On Thu, Mar 25, 2021 at 05:14:42PM +0200, Heikki Krogerus wrote:
> On Thu, Mar 25, 2021 at 10:41:09AM -0400, Alan Stern wrote:
> > On Thu, Mar 25, 2021 at 03:29:21PM +0300, Heikki Krogerus wrote:
> > > Introducing usb_for_each_port(). It works the same way as
> > > usb_for_each_dev(), but instead of going through every USB
> > > device in the system, it walks through the USB ports in the
> > > system.
> > >
> > > Signed-off-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> >
> > This has a couple of nasty errors.
> >
> > > ---
> > > drivers/usb/core/usb.c | 43 ++++++++++++++++++++++++++++++++++++++++++
> > > include/linux/usb.h | 1 +
> > > 2 files changed, 44 insertions(+)
> > >
> > > diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
> > > index 2ce3667ec6fae..6d49db9a1b208 100644
> > > --- a/drivers/usb/core/usb.c
> > > +++ b/drivers/usb/core/usb.c
> > > @@ -398,6 +398,49 @@ int usb_for_each_dev(void *data, int (*fn)(struct usb_device *, void *))
> > > }
> > > EXPORT_SYMBOL_GPL(usb_for_each_dev);
> > >
> > > +struct each_hub_arg {
> > > + void *data;
> > > + int (*fn)(struct device *, void *);
> > > +};
> > > +
> > > +static int __each_hub(struct device *dev, void *data)
> > > +{
> > > + struct each_hub_arg *arg = (struct each_hub_arg *)data;
> > > + struct usb_device *hdev = to_usb_device(dev);
> >
> > to_usb_device() won't work properly if the struct device isn't embedded
> > in an actual usb_device structure. And that will happen, since the USB
> > bus type holds usb_interface structures as well as usb_devices.
>
> OK, so I need to filter them out.
>
> > In fact, you should use usb_for_each_dev here; it already does what you
> > want.
>
> Unfortunately I can't use usb_for_each_dev here, because it deals with
> struct usb_device while I need to deal with struct device in the
> callback.
I see; the prototypes of arg->fn are different. Oh well, it's a shame
the code can't be reused. In any case, you should copy what
usb.c:__each_dev() does.
Alan Stern
> > > + struct usb_hub *hub;
> > > + int ret;
> > > + int i;
> > > +
> > > + hub = usb_hub_to_struct_hub(hdev);
> > > + if (!hub)
> > > + return 0;
> > > +
> > > + for (i = 0; i < hdev->maxchild; i++) {
> > > + ret = arg->fn(&hub->ports[i]->dev, arg->data);
> > > + if (ret)
> > > + return ret;
> > > + }
> > > +
> > > + return 0;
> > > +}
> >
> > Don't you need some sort of locking or refcounting here? What would
> > happen if this hub got removed while the routine was running?
>
> I'll use a lock then.
>
> thanks,
>
> --
> heikki
