block: split scsi_request out of struct request

And require all drivers that want to support BLOCK_PC to allocate it
as the first thing of their private data.  To support this the legacy
IDE and BSG code is switched to set cmd_size on their queues to let
the block layer allocate the additional space.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/ide.h b/include/linux/ide.h
index a633898..086fbe1 100644
--- a/include/linux/ide.h
+++ b/include/linux/ide.h
@@ -20,6 +20,7 @@
 #include <linux/mutex.h>
 /* for request_sense */
 #include <linux/cdrom.h>
+#include <scsi/scsi_cmnd.h>
 #include <asm/byteorder.h>
 #include <asm/io.h>
 
@@ -52,6 +53,11 @@ enum ata_cmd_type_bits {
 	((rq)->cmd_type == REQ_TYPE_ATA_PM_SUSPEND || \
 	 (rq)->cmd_type == REQ_TYPE_ATA_PM_RESUME)
 
+struct ide_request {
+	struct scsi_request sreq;
+	u8 sense[SCSI_SENSE_BUFFERSIZE];
+};
+
 /* Error codes returned in rq->errors to the higher part of the driver. */
 enum {
 	IDE_DRV_ERROR_GENERAL	= 101,
@@ -579,7 +585,7 @@ struct ide_drive_s {
 
 	/* current sense rq and buffer */
 	bool sense_rq_armed;
-	struct request sense_rq;
+	struct request *sense_rq;
 	struct request_sense sense_data;
 };