USB: skel_read really sucks royally
The read code path of the skeleton driver really sucks - skel_read works only for devices which always send data - the timeout comes out of thin air - it blocks signals for the duration of the timeout - it disallows nonblocking IO by design This patch fixes it by using a real urb, a completion and interruptible waits. Signed-off-by: Oliver Neukum <oliver@neukum.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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@ -52,15 +52,21 @@ struct usb_skel {
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struct usb_interface *interface; /* the interface for this device */
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struct semaphore limit_sem; /* limiting the number of writes in progress */
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struct usb_anchor submitted; /* in case we need to retract our submissions */
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struct urb *bulk_in_urb; /* the urb to read data with */
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unsigned char *bulk_in_buffer; /* the buffer to receive data */
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size_t bulk_in_size; /* the size of the receive buffer */
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size_t bulk_in_filled; /* number of bytes in the buffer */
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size_t bulk_in_copied; /* already copied to user space */
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__u8 bulk_in_endpointAddr; /* the address of the bulk in endpoint */
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__u8 bulk_out_endpointAddr; /* the address of the bulk out endpoint */
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int errors; /* the last request tanked */
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int open_count; /* count the number of openers */
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bool ongoing_read; /* a read is going on */
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bool processed_urb; /* indicates we haven't processed the urb */
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spinlock_t err_lock; /* lock for errors */
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struct kref kref;
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struct mutex io_mutex; /* synchronize I/O with disconnect */
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struct completion bulk_in_completion; /* to wait for an ongoing read */
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};
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#define to_skel_dev(d) container_of(d, struct usb_skel, kref)
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@ -71,6 +77,7 @@ static void skel_delete(struct kref *kref)
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{
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struct usb_skel *dev = to_skel_dev(kref);
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usb_free_urb(dev->bulk_in_urb);
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usb_put_dev(dev->udev);
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kfree(dev->bulk_in_buffer);
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kfree(dev);
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@ -174,38 +181,182 @@ static int skel_flush(struct file *file, fl_owner_t id)
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return res;
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}
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static void skel_read_bulk_callback(struct urb *urb)
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{
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struct usb_skel *dev;
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dev = urb->context;
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spin_lock(&dev->err_lock);
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/* sync/async unlink faults aren't errors */
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if (urb->status) {
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if(!(urb->status == -ENOENT ||
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urb->status == -ECONNRESET ||
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urb->status == -ESHUTDOWN))
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err("%s - nonzero write bulk status received: %d",
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__func__, urb->status);
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dev->errors = urb->status;
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} else {
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dev->bulk_in_filled = urb->actual_length;
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}
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dev->ongoing_read = 0;
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spin_unlock(&dev->err_lock);
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complete(&dev->bulk_in_completion);
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}
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static int skel_do_read_io(struct usb_skel *dev, size_t count)
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{
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int rv;
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/* prepare a read */
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usb_fill_bulk_urb(dev->bulk_in_urb,
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dev->udev,
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usb_rcvbulkpipe(dev->udev,
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dev->bulk_in_endpointAddr),
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dev->bulk_in_buffer,
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min(dev->bulk_in_size, count),
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skel_read_bulk_callback,
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dev);
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/* tell everybody to leave the URB alone */
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spin_lock_irq(&dev->err_lock);
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dev->ongoing_read = 1;
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spin_unlock_irq(&dev->err_lock);
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/* do it */
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rv = usb_submit_urb(dev->bulk_in_urb, GFP_KERNEL);
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if (rv < 0) {
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err("%s - failed submitting read urb, error %d",
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__func__, rv);
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dev->bulk_in_filled = 0;
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rv = (rv == -ENOMEM) ? rv : -EIO;
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spin_lock_irq(&dev->err_lock);
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dev->ongoing_read = 0;
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spin_unlock_irq(&dev->err_lock);
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}
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return rv;
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}
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static ssize_t skel_read(struct file *file, char *buffer, size_t count, loff_t *ppos)
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{
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struct usb_skel *dev;
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int retval;
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int bytes_read;
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int rv;
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bool ongoing_io;
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dev = (struct usb_skel *)file->private_data;
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mutex_lock(&dev->io_mutex);
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/* if we cannot read at all, return EOF */
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if (!dev->bulk_in_urb || !count)
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return 0;
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/* no concurrent readers */
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rv = mutex_lock_interruptible(&dev->io_mutex);
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if (rv < 0)
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return rv;
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if (!dev->interface) { /* disconnect() was called */
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retval = -ENODEV;
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rv = -ENODEV;
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goto exit;
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}
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/* do a blocking bulk read to get data from the device */
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retval = usb_bulk_msg(dev->udev,
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usb_rcvbulkpipe(dev->udev, dev->bulk_in_endpointAddr),
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dev->bulk_in_buffer,
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min(dev->bulk_in_size, count),
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&bytes_read, 10000);
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/* if IO is under way, we must not touch things */
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retry:
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spin_lock_irq(&dev->err_lock);
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ongoing_io = dev->ongoing_read;
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spin_unlock_irq(&dev->err_lock);
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/* if the read was successful, copy the data to userspace */
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if (!retval) {
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if (copy_to_user(buffer, dev->bulk_in_buffer, bytes_read))
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retval = -EFAULT;
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else
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retval = bytes_read;
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if (ongoing_io) {
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/*
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* IO may take forever
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* hence wait in an interruptible state
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*/
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rv = wait_for_completion_interruptible(&dev->bulk_in_completion);
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if (rv < 0)
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goto exit;
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/*
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* by waiting we also semiprocessed the urb
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* we must finish now
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*/
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dev->bulk_in_copied = 0;
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dev->processed_urb = 1;
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}
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if (!dev->processed_urb) {
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/*
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* the URB hasn't been processed
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* do it now
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*/
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wait_for_completion(&dev->bulk_in_completion);
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dev->bulk_in_copied = 0;
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dev->processed_urb = 1;
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}
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/* errors must be reported */
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if ((rv = dev->errors) < 0) {
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/* any error is reported once */
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dev->errors = 0;
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/* to preserve notifications about reset */
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rv = (rv == -EPIPE) ? rv : -EIO;
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/* no data to deliver */
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dev->bulk_in_filled = 0;
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/* report it */
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goto exit;
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}
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/*
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* if the buffer is filled we may satisfy the read
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* else we need to start IO
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*/
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if (dev->bulk_in_filled) {
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/* we had read data */
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size_t available = dev->bulk_in_filled - dev->bulk_in_copied;
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size_t chunk = min(available, count);
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if (!available) {
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/*
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* all data has been used
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* actual IO needs to be done
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*/
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rv = skel_do_read_io(dev, count);
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if (rv < 0)
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goto exit;
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else
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goto retry;
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}
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/*
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* data is available
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* chunk tells us how much shall be copied
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*/
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if (copy_to_user(buffer,
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dev->bulk_in_buffer + dev->bulk_in_copied,
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chunk))
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rv = -EFAULT;
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else
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rv = chunk;
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dev->bulk_in_copied += chunk;
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/*
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* if we are asked for more than we have,
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* we start IO but don't wait
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*/
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if (available < count)
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skel_do_read_io(dev, count - chunk);
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} else {
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/* no data in the buffer */
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rv = skel_do_read_io(dev, count);
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if (rv < 0)
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goto exit;
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else
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goto retry;
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}
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exit:
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mutex_unlock(&dev->io_mutex);
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return retval;
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return rv;
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}
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static void skel_write_bulk_callback(struct urb *urb)
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@ -363,6 +514,7 @@ static int skel_probe(struct usb_interface *interface, const struct usb_device_i
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mutex_init(&dev->io_mutex);
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spin_lock_init(&dev->err_lock);
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init_usb_anchor(&dev->submitted);
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init_completion(&dev->bulk_in_completion);
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dev->udev = usb_get_dev(interface_to_usbdev(interface));
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dev->interface = interface;
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@ -384,6 +536,11 @@ static int skel_probe(struct usb_interface *interface, const struct usb_device_i
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err("Could not allocate bulk_in_buffer");
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goto error;
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}
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dev->bulk_in_urb = usb_alloc_urb(0, GFP_KERNEL);
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if (!dev->bulk_in_urb) {
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err("Could not allocate bulk_in_urb");
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goto error;
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}
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}
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if (!dev->bulk_out_endpointAddr &&
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@ -453,6 +610,7 @@ static void skel_draw_down(struct usb_skel *dev)
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time = usb_wait_anchor_empty_timeout(&dev->submitted, 1000);
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if (!time)
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usb_kill_anchored_urbs(&dev->submitted);
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usb_kill_urb(dev->bulk_in_urb);
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}
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static int skel_suspend(struct usb_interface *intf, pm_message_t message)
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