xen/blk[front|back]: Squash blkif_request_rw and blkif_request_discard together

In a union type structure to deal with the overlapping
attributes in a easier manner.

Suggested-by: Ian Campbell <Ian.Campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 17 insertions, 7 deletions

diff --git a/include/xen/interface/io/blkif.h b/include/xen/interface/io/blkif.h
index 9324488f23f0..f88e28b6a27c 100644
--- a/include/xen/interface/io/blkif.h
+++ b/include/xen/interface/io/blkif.h
@@ -95,6 +95,12 @@ typedef uint64_t blkif_sector_t;
 #define BLKIF_MAX_SEGMENTS_PER_REQUEST 11
 
 struct blkif_request_rw {
+        uint8_t        nr_segments;  /* number of segments                   */
+        blkif_vdev_t   handle;       /* only for read/write requests         */
+#ifdef CONFIG_X86_64
+        uint32_t       _pad1;        /* offsetof(blkif_request,u.rw.id) == 8 */
+#endif
+        uint64_t       id;           /* private guest value, echoed in resp  */
         blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
         struct blkif_request_segment {
                 grant_ref_t gref;        /* reference to I/O buffer frame        */
@@ -102,23 +108,27 @@ struct blkif_request_rw {
                 /* @last_sect: last sector in frame to transfer (inclusive).     */
                 uint8_t     first_sect, last_sect;
         } seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
-};
+} __attribute__((__packed__));
 
 struct blkif_request_discard {
+        uint8_t        nr_segments;  /* number of segments                   */
+        blkif_vdev_t   _pad1;        /* only for read/write requests         */
+#ifdef CONFIG_X86_64
+        uint32_t       _pad2;        /* offsetof(blkif_req..,u.discard.id)==8*/
+#endif
+        uint64_t       id;           /* private guest value, echoed in resp  */
         blkif_sector_t sector_number;
-        uint64_t nr_sectors;
-};
+        uint64_t       nr_sectors;
+        uint8_t        _pad3;
+} __attribute__((__packed__));
 
 struct blkif_request {
         uint8_t        operation;    /* BLKIF_OP_???                         */
-        uint8_t        nr_segments;  /* number of segments                   */
-        blkif_vdev_t   handle;       /* only for read/write requests         */
-        uint64_t       id;           /* private guest value, echoed in resp  */
         union {
                 struct blkif_request_rw rw;
                 struct blkif_request_discard discard;
         } u;
-};
+} __attribute__((__packed__));
 
 struct blkif_response {
         uint64_t        id;              /* copied from request */