Re: how can i make the skeleton read function blocking function?

On 4/24/07, Oliver Neukum <[email protected]> wrote:
> Am Dienstag, 24. April 2007 12:06 schrieb Wael Adel:
> > On 4/24/07, Oliver Neukum <[email protected]> wrote:
> > > Am Dienstag, 24. April 2007 11:46 schrieb Wael Adel:
> > > >         retval = usb_submit_urb(urb, GFP_KERNEL);
> > > >         if (retval) {
> > > >                 err("%s - failed submitting write urb, error %d",
> > > __FUNCTION__, retval);
> > > >                 goto error;
> > > >         }
> > > >
> > > >         if (buf != NULL)
> > > >         {
> > > >                 if (copy_to_user(user_buffer, buf , readsize))
> > > >                 {
> > > >                         retval = -EFAULT;
> > > >                         goto error;
> > > >                 }
> > > >         }
> > >
> > > You are copying the the buffer to user space without waiting for the
> > > URB to be executed. That cannot work.
> >
> > so how can i wait for the urb to be executed then copying the data to
> > the user space?
> > is there a flag that i should loop on it or what?
>
> - init an instance of "struct completion"
> - submit the URB, passing a pointer to the struct completion
> - use wait_for_completion()
>
> - in the completion handler call complete()


so these are the required modifications required to wait until the urb
is finished then i can transfer the read data to the user-space

***********************************************************************************************************************
static void skel_read_bulk_callback(struct urb *urb, struct pt_regs *regs)
{
	struct usb_skel *dev;
	complete((struct completion *)urb->context);
	dev = (struct usb_skel *)urb->context;


	/* sync/async unlink faults aren't errors */
	if (urb->status &&
	    !(urb->status == -ENOENT ||
	      urb->status == -ECONNRESET ||
	      urb->status == -ESHUTDOWN)) {
		dbg("%s - nonzero write bulk status received: %d",
		    __FUNCTION__, urb->status);
	}

	/* free up our allocated buffer */
	usb_buffer_free(urb->dev, urb->transfer_buffer_length,
			urb->transfer_buffer, urb->transfer_dma);
	up(&dev->limit_sem);
}

static ssize_t skel_read(struct file *file, const char *user_buffer,
size_t count, loff_t *ppos)
{
	struct completion done;
	struct usb_skel *dev;
	int retval = 0,readbytes;
	struct urb *urb = NULL;
	char *buf = NULL;
	size_t readsize = min(count, (size_t)MAX_TRANSFER);

	dev = (struct usb_skel *)file->private_data;

	/* verify that we actually have some data to write */
	if (count == 0)
		goto exit;

	/* limit the number of URBs in flight to stop a user from using up all RAM */
	if (down_interruptible(&dev->limit_sem)) {
		retval = -ERESTARTSYS;
		goto exit;
	}

	/* create a urb, and a buffer for it, and copy the data to the urb */
	urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!urb) {
		retval = -ENOMEM;
		goto error;
	}

	buf = usb_buffer_alloc(dev->udev, readsize, GFP_KERNEL, &urb->transfer_dma);
	if (!buf) {
		retval = -ENOMEM;
		goto error;
	}

	/* initialize the urb properly */
	usb_fill_bulk_urb(urb, dev->udev,
			  usb_rcvbulkpipe(dev->udev, dev->bulk_in_endpointAddr),
			  buf, readsize, skel_read_bulk_callback, dev);
	urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;

	/* send the data out the bulk port */
	retval = usb_submit_urb(urb, GFP_KERNEL);
	if (retval) {
		err("%s - failed submitting write urb, error %d", __FUNCTION__, retval);
		goto error;
	}

	wait_for_completion(&done);

	if (   copy_to_user(user_buffer, dev->bulk_in_buffer, readbytes) )
		retval = -EFAULT;
	else
		retval = readbytes;


	return retval;

	/* release our reference to this urb, the USB core will eventually
free it entirely */
	usb_free_urb(urb);

exit:
	return readsize;

error:
	usb_buffer_free(dev->udev, readsize, buf, urb->transfer_dma);
	usb_free_urb(urb);
	up(&dev->limit_sem);
	return retval;
}
*********************************************************************************************************************
is it right? or there is something else i should adjust.
thanks in advance.

>
> 	HTH
> 		Oliver
> --
> SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nürnberg)
> This signature is a legal requirement
>

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