ioctl: Rearrange members in nvme_dsm_args

Avoid any holes in the struct by rearranging the members. Also add the
attribute packed to struct definition to reduce ABI breakage.

struct nvme_dsm_args {
        int                        args_size;            /*     0     4 */
        int                        fd;                   /*     4     4 */
        __u32 *                    result;               /*     8     8 */
        __u32                      timeout;              /*    16     4 */
        __u32                      nsid;                 /*    20     4 */
        struct nvme_dsm_range *    dsm;                  /*    24     8 */
        __u32                      attrs;                /*    32     4 */
        __u16                      nr_ranges;            /*    36     2 */

        /* size: 40, cachelines: 1, members: 8 */
        /* padding: 2 */
        /* last cacheline: 40 bytes */
} __attribute__((__aligned__(8)));

Signed-off-by: Daniel Wagner <[email protected]>

Author: dwsuse

src/nvme/ioctl.h

@@ -3709,23 +3709,23 @@ static inline int nvme_verify(struct nvme_io_args *args)
 /**
  * nvme_dsm_args - Arguments for the NVMe Dataset Management command
  * @fd:		File descriptor of nvme device
+ * @result:	The command completion result from CQE dword0
+ * @timeout:	Timeout in ms
  * @nsid:	Namespace identifier
+ * @dsm:	The data set management attributes
  * @attrs:	DSM attributes, see &enum nvme_dsm_attributes
  * @nr_ranges:	Number of block ranges in the data set management attributes
- * @dsm:	The data set management attributes
- * @timeout:	Timeout in ms
- * @result:	The command completion result from CQE dword0
  */
 struct nvme_dsm_args {
 	int args_size;
 	int fd;
+	__u32 *result;
+	__u32 timeout;
 	__u32 nsid;
+	struct nvme_dsm_range *dsm;
 	__u32 attrs;
 	__u16 nr_ranges;
-	struct nvme_dsm_range *dsm;
-	__u32 timeout;
-	__u32 *result;
-};
+} __attribute__((packed, aligned(__alignof__(__u32*))));
 
 /**
  * nvme_dsm() - Send an nvme data set management command