Am Freitag, den 24.03.2017, 22:50 +0100 schrieb Tobias Herzog:
> Hi Oliver,
>
> thank you for your patience... :) I have a question to one of your
> comments (see below).
>
> Best regards,
> Tobias
>
> >
> > Am Samstag, den 18.03.2017, 19:52 +0100 schrieb Tobias Herzog:
> > >
> > >
> > > USB devices may have very limitited endpoint packet sizes, so that
> > > notifications can not be transferred within one single usb packet.
> > > Reassembling of multiple packages may be necessary.
> > Hi,
> >
> > almost perfect.
> > A few new issue. Comments inline.
> >
> > >
> > >
> > >
> > > + struct usb_cdc_notification *dr = (struct
> > > usb_cdc_notification *)buf;
> > > + unsigned char *data = (unsigned char *)(dr + 1);
> > This is border line incorrect. It depends on the compiler not
> > adding padding. Please make it
> >
> > buf + sizeof(struct usb_cdc_notification)
> >
> > >
> > >
> > > - usb_mark_last_busy(acm->dev);
> > > -
> > > - data = (unsigned char *)(dr + 1);
> > > switch (dr->bNotificationType) {
> > > case USB_CDC_NOTIFY_NETWORK_CONNECTION:
> > > dev_dbg(&acm->control->dev,
> > > @@ -363,8 +337,77 @@ static void acm_ctrl_irq(struct urb *urb)
> > > __func__,
> > > dr->bNotificationType, dr->wIndex,
> > > dr->wLength, data[0], data[1]);
> > > + }
> > > +}
> > > +
> > > +/* control interface reports status changes with "interrupt"
> > > transfers */
> > > +static void acm_ctrl_irq(struct urb *urb)
> > > +{
> > > + struct acm *acm = urb->context;
> > > + struct usb_cdc_notification *dr = urb->transfer_buffer;
> > > + unsigned int current_size = urb->actual_length;
> > > + unsigned int expected_size, copy_size;
> > > + int retval;
> > > + int status = urb->status;
> > > +
> > > + switch (status) {
> > > + case 0:
> > > + /* success */
> > > break;
> > > + case -ECONNRESET:
> > > + case -ENOENT:
> > > + case -ESHUTDOWN:
> > > + /* this urb is terminated, clean up */
> > > + acm->nb_index = 0;
> > > + dev_dbg(&acm->control->dev,
> > > + "%s - urb shutting down with status:
> > > %d\n",
> > > + __func__, status);
> > > + return;
> > > + default:
> > > + dev_dbg(&acm->control->dev,
> > > + "%s - nonzero urb status received: %d\n",
> > > + __func__, status);
> > > + goto exit;
> > > }
> > > +
> > > + usb_mark_last_busy(acm->dev);
> > > +
> > > + if (acm->nb_index)
> > > + dr = (struct usb_cdc_notification *)acm-
> > > >
> > > > notification_buffer;
> > > +
> > > + /* size = notification-header + (optional) data */
> > > + expected_size = sizeof(struct usb_cdc_notification) +
> > > + le16_to_cpu(dr->wLength);
> > > +
> > > + if (current_size < expected_size) {
> > > + /* notification is transmitted fragmented,
> > > reassemble */
> > > + if (acm->nb_size < expected_size) {
> > > + if (acm->nb_size) {
> > > + kfree(acm->notification_buffer);
> > > + acm->nb_size = 0;
> > > + }
> > > + acm->notification_buffer =
> > > + kmalloc(expected_size,
> > > GFP_ATOMIC);
> > Given how kmalloc works you'd better round this up to a power of two.
> >
> > >
> > >
> > > + if (!acm->notification_buffer)
> > > + goto exit;
> > This is most subtle. Please add a comment that this prevents a double
> > free if we get a disconnect()
> I'm unsure if I got this right: Are you talking about the fact, that
> the use of 'kmalloc' will make 'acm->notification_buffer' valid again
> (i.e. NULL or pointing to a correctly allocated block), after it was
yes
> "invalidated" by 'kfree' (in case the previously allocated buffer was
> too small)?
> The 'goto exit'-thing for me is just not to use the buffer if
> allocation fails. Or am I missing anything here?
You need to consider the hot unplug case.
Regards
Oliver
