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.kroge...@linux.intel.com>
> > 
> > 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

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