compat_ioctl: bsg: add handler

bsg_ioctl() calls into scsi_cmd_ioctl() for a couple of generic commands
and relies on fs/compat_ioctl.c to handle it correctly in compat mode.

Adding a private compat_ioctl() handler avoids that round-trip and lets
us get rid of the generic emulation once this is done.

Note that bsg implements an SG_IO command that is different from the
other drivers and does not need emulation.
Reviewed-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

block/bsg.c

@@ -382,6 +382,7 @@ static const struct file_operations bsg_fops = {
 	.open		=	bsg_open,
 	.release	=	bsg_release,
 	.unlocked_ioctl	=	bsg_ioctl,
+	.compat_ioctl	=	compat_ptr_ioctl,
 	.owner		=	THIS_MODULE,
 	.llseek		=	default_llseek,
 };