uio: add ioctl to uio

In TCMU, if backstore holds its own userspace buffer, for read cmd, the
data needs to be copied from userspace buffer to tcmu data area first,
and then needs to be copied from tcmu data area to scsi sgl pages again.

To solve this problem, add ioctl to uio to let userspace backstore can
copy data between scsi sgl pages and its own buffer directly.

Reviewed-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>

drivers/uio/uio.c

@@ -815,6 +815,24 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
 	return ret;
 }
 
+long uio_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
+{
+	struct uio_listener *listener = filep->private_data;
+	struct uio_device *idev = listener->dev;
+	long retval = 0;
+
+	mutex_lock(&idev->info_lock);
+	if (!idev->info || !idev->info->ioctl) {
+		retval = -EINVAL;
+		goto out;
+	}
+
+	retval = idev->info->ioctl(idev->info, cmd, arg);
+out:
+	mutex_unlock(&idev->info_lock);
+	return retval;
+}
+
 static const struct file_operations uio_fops = {
 	.owner		= THIS_MODULE,
 	.open		= uio_open,
@@ -825,6 +843,10 @@ static const struct file_operations uio_fops = {
 	.poll		= uio_poll,
 	.fasync		= uio_fasync,
 	.llseek		= noop_llseek,
+	.unlocked_ioctl = uio_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl   = uio_ioctl,
+#endif
 };
 
 static int uio_major_init(void)

include/linux/uio_driver.h

@@ -109,6 +109,7 @@ struct uio_info {
 	int (*open)(struct uio_info *info, struct inode *inode);
 	int (*release)(struct uio_info *info, struct inode *inode);
 	int (*irqcontrol)(struct uio_info *info, s32 irq_on);
+	long (*ioctl)(struct uio_info *info, unsigned int cmd, unsigned long arg);
 };
 
 extern int __must_check