Re: [PATCH 1/4] cdc-acm: reassemble fragmented notifications

[Tobias Herzog <t-herzog@gmx.de>]

Hi,

thank you for your feedback. I tried to fix all issues with v2. I was
just unsure with one point (see comment).


/tobias


> Am Dienstag, den 14.03.2017, 21:14 +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,
> 
> thank you for the patch. Unfortunately it has some issue.
> Please see the comments inside.
> 
> 	Regards
> 		Oliver
> 
> > 
> > 
> > Signed-off-by: Tobias Herzog <t-herzog@gmx.de>
> > ---
> >  drivers/usb/class/cdc-acm.c | 102 +++++++++++++++++++++++++++++++-
> > ------------
> >  drivers/usb/class/cdc-acm.h |   2 +
> >  2 files changed, 75 insertions(+), 29 deletions(-)
> > 
> > diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-
> > acm.c
> > index e35b150..40714fe 100644
> > --- a/drivers/usb/class/cdc-acm.c
> > +++ b/drivers/usb/class/cdc-acm.c
> > @@ -282,39 +282,13 @@ static DEVICE_ATTR(iCountryCodeRelDate,
> > S_IRUGO, show_country_rel_date, NULL);
> >   * Interrupt handlers for various ACM device responses
> >   */
> >  
> > -/* control interface reports status changes with "interrupt"
> > transfers */
> > -static void acm_ctrl_irq(struct urb *urb)
> > +static void acm_process_notification(struct acm *acm, unsigned
> > char *buf)
> >  {
> > -	struct acm *acm = urb->context;
> > -	struct usb_cdc_notification *dr = urb->transfer_buffer;
> > -	unsigned char *data;
> >  	int newctrl;
> >  	int difference;
> > -	int retval;
> > -	int status = urb->status;
> > +	struct usb_cdc_notification *dr = (struct
> > usb_cdc_notification *)buf;
> > +	unsigned char *data = (unsigned char *)(dr + 1);
> >  
> > -	switch (status) {
> > -	case 0:
> > -		/* success */
> > -		break;
> > -	case -ECONNRESET:
> > -	case -ENOENT:
> > -	case -ESHUTDOWN:
> > -		/* this urb is terminated, clean up */
> > -		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);
> > -
> > -	data = (unsigned char *)(dr + 1);
> >  	switch (dr->bNotificationType) {
> >  	case USB_CDC_NOTIFY_NETWORK_CONNECTION:
> >  		dev_dbg(&acm->control->dev,
> > @@ -363,8 +337,74 @@ 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 */
> > +		kfree(acm->notification_buffer);
> > +		acm->notification_buffer = NULL;
> Why? Disconnect() will free it anyway. It should be enough
> to discard the content.
> 
> > 
> > +		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->notification_buffer)
> > +		dr = (struct usb_cdc_notification *)acm-
> > >notification_buffer;
> > +
> > +	/* assume the first package contains at least two bytes */
> > +	expected_size = dr->wLength + 8;
> You need the explain where you got the 8 from. In fact a define would
> be best.
I feel better to use 'sizeof(struct usb_cdc_notification)' here, than
using an separate, hard-coded define. In fact this is really what we
want here, as the buffer needs to cover the notification header (i.e.
struct usb_cdc_notification) + the additional (optional) data.

> 
> > 
> > +
> > +	if (current_size < expected_size) {
> > +		/* notification is transmitted framented,
> > reassemble */
> Please fix the typo.
> 
> > 
> > +		if (!acm->notification_buffer) {
> > +			acm->notification_buffer =
> > +					kmalloc(expected_size,
> > GFP_ATOMIC);
> This can fail. You _must_ check for that.
> 
> > 
> > +			acm->nb_index = 0;
> > +		}
> > +
> > +		copy_size = min(current_size,
> > +				expected_size - acm->nb_index);
> > +
> > +		memcpy(&acm->notification_buffer[acm->nb_index],
> > +		       urb->transfer_buffer, copy_size);
> > +		acm->nb_index += copy_size;
> > +		current_size = acm->nb_index;
> > +	}
> > +
> > +	if (current_size < expected_size)
> > +		goto exit;
> This is an unneeded goto.
> 
> > 
> > +	/* notification complete */
> > +	acm_process_notification(acm, (unsigned char *)dr);
> > +
> > +	kfree(acm->notification_buffer);
> Why? If one message was fragmented, the next one will also likely be
> fragmented. Why release the buffer before you know whether it can be
> reused?
> 
> > 
> > +	acm->notification_buffer = NULL;
> > +
> >  exit:
> >  	retval = usb_submit_urb(urb, GFP_ATOMIC);
> >  	if (retval && retval != -EPERM)
> > @@ -1488,6 +1528,8 @@ static int acm_probe(struct usb_interface
> > *intf,
> >  			 epctrl->bInterval ? epctrl->bInterval :
> > 16);
> >  	acm->ctrlurb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
> >  	acm->ctrlurb->transfer_dma = acm->ctrl_dma;
> > +	acm->notification_buffer = NULL;
> > +	acm->nb_index = 0;
> >  
> >  	dev_info(&intf->dev, "ttyACM%d: USB ACM device\n", minor);
> >  
> > @@ -1580,6 +1622,8 @@ static void acm_disconnect(struct
> > usb_interface *intf)
> >  	usb_free_coherent(acm->dev, acm->ctrlsize, acm-
> > >ctrl_buffer, acm->ctrl_dma);
> >  	acm_read_buffers_free(acm);
> >  
> > +	kfree(acm->notification_buffer);
> > +
> >  	if (!acm->combined_interfaces)
> >  		usb_driver_release_interface(&acm_driver, intf ==
> > acm->control ?
> >  					acm->data : acm->control);
> > diff --git a/drivers/usb/class/cdc-acm.h b/drivers/usb/class/cdc-
> > acm.h
> > index c980f11..bc07fb2 100644
> > --- a/drivers/usb/class/cdc-acm.h
> > +++ b/drivers/usb/class/cdc-acm.h
> > @@ -98,6 +98,8 @@ struct acm {
> >  	struct acm_wb *putbuffer;			/* for
> > acm_tty_put_char() */
> >  	int rx_buflimit;
> >  	spinlock_t read_lock;
> > +	u8 *notification_buffer;			/* to
> > reassemble fragmented notifications */
> > +	unsigned int nb_index;
> >  	int write_used;					/*
> > number of non-empty write buffers */
> >  	int transmitting;
> >  	spinlock_t write_lock;