Restoring joydev BTNMAP ioctl compatibility

[Stephen Kitt <steve@sk2.org>]

Hi,

The KEY_MAX change in 2.6.28 changed the definitions of the button map
joydev ioctls (JSIOCSBTNMAP and JSIOCGBTNMAP). Thus software built using
pre-2.6.28 headers fails when retrieving or setting the button map on 2.6.28
and greater kernels.

The attached patch reintroduced the old ioctl definitions to restore
compatibility. It only copies as much information as was supported in
previous versions, but since this still allows for devices with 256 buttons I
doubt there's much chance of losing information, hence the lack of a printk()
warning.

Signed-off-by: Stephen Kitt <steve@sk2.org>

 joydev.c |   23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/input/joydev.c b/drivers/input/joydev.c
index 4cfd084..764700e 100644
--- a/drivers/input/joydev.c
+++ b/drivers/input/joydev.c
@@ -35,6 +35,11 @@ MODULE_LICENSE("GPL");
 #define JOYDEV_MINORS		16
 #define JOYDEV_BUFFER_SIZE	64
 
+/* Support for old ioctls using the old value of KEY_MAX. */
+#define OLD_KEY_MAX		0x1ff
+#define OLD_JSIOCSBTNMAP	_IOW('j', 0x33, __u16[OLD_KEY_MAX - BTN_MISC + 1])
+#define OLD_JSIOCGBTNMAP	_IOR('j', 0x34, __u16[OLD_KEY_MAX - BTN_MISC + 1])
+
 struct joydev {
 	int exist;
 	int open;
@@ -529,10 +534,28 @@ static int joydev_ioctl_common(struct joydev *joydev,
 
 		return 0;
 
+	case OLD_JSIOCSBTNMAP:
+		if (copy_from_user(joydev->keypam, argp,
+				   sizeof(__u16) * (OLD_KEY_MAX - BTN_MISC + 1)))
+			return -EFAULT;
+
+		for (i = 0; i < joydev->nkey && i < OLD_KEY_MAX - BTN_MISC + 1; i++) {
+			if (joydev->keypam[i] > KEY_MAX ||
+			    joydev->keypam[i] < BTN_MISC)
+				return -EINVAL;
+			joydev->keymap[joydev->keypam[i] - BTN_MISC] = i;
+		}
+
+		return 0;
+
 	case JSIOCGBTNMAP:
 		return copy_to_user(argp, joydev->keypam,
 			sizeof(__u16) * (KEY_MAX - BTN_MISC + 1)) ? -EFAULT : 0;
 
+	case OLD_JSIOCGBTNMAP:
+		return copy_to_user(argp, joydev->keypam,
+				    sizeof(__u16) * (OLD_KEY_MAX - BTN_MISC + 1)) ? -EFAULT : 0;
+
 	default:
 		if ((cmd & ~IOCSIZE_MASK) == JSIOCGNAME(0)) {
 			int len;