usb: usbtmc: Add ioctl USBTMC_IOCTL_API_VERSION

Add ioctl USBTMC_IOCTL_API_VERSION to get current API version
of usbtmc driver.

This is to allow an instrument library to determine whether
the driver API is compatible with the implementation.

The API may change in future versions. Therefore the macro
USBTMC_API_VERSION should be incremented when changing tmc.h
with new flags, ioctls or when changing a significant behavior
of the driver.
Signed-off-by: Guido Kiener <guido.kiener@rohde-schwarz.com>
Reviewed-by: Steve Bayless <steve_bayless@keysight.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/usbtmc.c

@@ -22,6 +22,10 @@
 #include <linux/compat.h>
 #include <linux/usb/tmc.h>
 
+/* Increment API VERSION when changing tmc.h with new flags or ioctls
+ * or when changing a significant behavior of the driver.
+ */
+#define USBTMC_API_VERSION (2)
 
 #define USBTMC_HEADER_SIZE	12
 #define USBTMC_MINOR_BASE	176
@@ -2179,6 +2183,11 @@ static long usbtmc_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 						   (void __user *)arg);
 		break;
 
+	case USBTMC_IOCTL_API_VERSION:
+		retval = put_user(USBTMC_API_VERSION,
+				  (__u32 __user *)arg);
+		break;
+
 	case USBTMC488_IOCTL_GET_CAPS:
 		retval = copy_to_user((void __user *)arg,
 				&data->usb488_caps,

include/uapi/linux/usb/tmc.h

@@ -89,6 +89,7 @@ struct usbtmc_message {
 #define USBTMC_IOCTL_WRITE		_IOWR(USBTMC_IOC_NR, 13, struct usbtmc_message)
 #define USBTMC_IOCTL_READ		_IOWR(USBTMC_IOC_NR, 14, struct usbtmc_message)
 #define USBTMC_IOCTL_WRITE_RESULT	_IOWR(USBTMC_IOC_NR, 15, __u32)
+#define USBTMC_IOCTL_API_VERSION	_IOR(USBTMC_IOC_NR, 16, __u32)
 
 #define USBTMC488_IOCTL_GET_CAPS	_IOR(USBTMC_IOC_NR, 17, unsigned char)
 #define USBTMC488_IOCTL_READ_STB	_IOR(USBTMC_IOC_NR, 18, unsigned char)