cdrom: factor out a cdrom_read_tocentry helper

Factor out a version of the CDROMREADTOCENTRY ioctl handler that can
be called directly from kernel space.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/cdrom.h

@@ -94,6 +94,9 @@ struct cdrom_device_ops {
 			       struct packet_command *);
 };
 
+int cdrom_read_tocentry(struct cdrom_device_info *cdi,
+		struct cdrom_tocentry *entry);
+
 /* the general block_device operations structure: */
 extern int cdrom_open(struct cdrom_device_info *cdi, struct block_device *bdev,
 			fmode_t mode);