nvme: add NVME_SC_CANCELLED

BugLink: http://bugs.launchpad.net/bugs/1531539

To properly document how we are using a negative Linux error value to
communicate request cancellations inside the driver.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit 297465c8)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/nvme/host/nvme.h

@@ -19,6 +19,16 @@
 #include <linux/kref.h>
 #include <linux/blk-mq.h>
 
+enum {
+	/*
+	 * Driver internal status code for commands that were cancelled due
+	 * to timeouts or controller shutdown.  The value is negative so
+	 * that it a) doesn't overlap with the unsigned hardware error codes,
+	 * and b) can easily be tested for.
+	 */
+	NVME_SC_CANCELLED		= -EINTR,
+};
+
 extern unsigned char nvme_io_timeout;
 #define NVME_IO_TIMEOUT	(nvme_io_timeout * HZ)
 

drivers/nvme/host/pci.c

@@ -621,7 +621,7 @@ static void req_completion(struct nvme_queue *nvmeq, void *ctx,
 
 		if (req->cmd_type == REQ_TYPE_DRV_PRIV) {
 			if (cmd_rq->ctx == CMD_CTX_CANCELLED)
-				error = -EINTR;
+				error = NVME_SC_CANCELLED;
 			else
 				error = status;
 		} else {