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, 36 insertions, 28 deletions

diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index dfb1b3a43a5d..dbfe7b3b0737 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -60,58 +60,66 @@ struct blkif_common_response {
         char dummy;
 };
 
-/* i386 protocol version */
-#pragma pack(push, 4)
-
 struct blkif_x86_32_request_rw {
+        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  */
         blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
         struct blkif_request_segment seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
-};
+} __attribute__((__packed__));
 
 struct blkif_x86_32_request_discard {
+        uint8_t        nr_segments;  /* number of segments                   */
+        blkif_vdev_t   _pad1;        /* was "handle" for read/write requests */
+        uint64_t       id;           /* private guest value, echoed in resp  */
         blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
-        uint64_t nr_sectors;
-};
+        uint64_t       nr_sectors;
+} __attribute__((__packed__));
 
 struct blkif_x86_32_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_x86_32_request_rw rw;
                 struct blkif_x86_32_request_discard discard;
         } u;
-};
+} __attribute__((__packed__));
+
+/* i386 protocol version */
+#pragma pack(push, 4)
 struct blkif_x86_32_response {
         uint64_t        id;              /* copied from request */
         uint8_t         operation;       /* copied from request */
         int16_t         status;          /* BLKIF_RSP_???       */
 };
 #pragma pack(pop)
-
 /* x86_64 protocol version */
 
 struct blkif_x86_64_request_rw {
+        uint8_t        nr_segments;  /* number of segments                   */
+        blkif_vdev_t   handle;       /* only for read/write requests         */
+        uint32_t       _pad1;        /* offsetof(blkif_reqest..,u.rw.id)==8  */
+        uint64_t       id;
         blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
         struct blkif_request_segment seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
-};
+} __attribute__((__packed__));
 
 struct blkif_x86_64_request_discard {
+        uint8_t        nr_segments;  /* number of segments                   */
+        blkif_vdev_t   _pad1;        /* was "handle" for read/write requests */
+        uint32_t       _pad2;        /* offsetof(blkif_..,u.discard.id)==8   */
+        uint64_t       id;
         blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
-        uint64_t nr_sectors;
-};
+        uint64_t       nr_sectors;
+} __attribute__((__packed__));
 
 struct blkif_x86_64_request {
         uint8_t        operation;    /* BLKIF_OP_???                         */
-        uint8_t        nr_segments;  /* number of segments                   */
-        blkif_vdev_t   handle;       /* only for read/write requests         */
-        uint64_t       __attribute__((__aligned__(8))) id;
         union {
                 struct blkif_x86_64_request_rw rw;
                 struct blkif_x86_64_request_discard discard;
         } u;
-};
+} __attribute__((__packed__));
+
 struct blkif_x86_64_response {
         uint64_t       __attribute__((__aligned__(8))) id;
         uint8_t         operation;       /* copied from request */
@@ -237,18 +245,18 @@ static inline void blkif_get_x86_32_req(struct blkif_request *dst,
 {
         int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST;
         dst->operation = src->operation;
-        dst->nr_segments = src->nr_segments;
-        dst->handle = src->handle;
-        dst->id = src->id;
         switch (src->operation) {
         case BLKIF_OP_READ:
         case BLKIF_OP_WRITE:
         case BLKIF_OP_WRITE_BARRIER:
         case BLKIF_OP_FLUSH_DISKCACHE:
+                dst->u.rw.nr_segments = src->u.rw.nr_segments;
+                dst->u.rw.handle = src->u.rw.handle;
+                dst->u.rw.id = src->u.rw.id;
                 dst->u.rw.sector_number = src->u.rw.sector_number;
                 barrier();
-                if (n > dst->nr_segments)
-                        n = dst->nr_segments;
+                if (n > dst->u.rw.nr_segments)
+                        n = dst->u.rw.nr_segments;
                 for (i = 0; i < n; i++)
                         dst->u.rw.seg[i] = src->u.rw.seg[i];
                 break;
@@ -266,18 +274,18 @@ static inline void blkif_get_x86_64_req(struct blkif_request *dst,
 {
         int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST;
         dst->operation = src->operation;
-        dst->nr_segments = src->nr_segments;
-        dst->handle = src->handle;
-        dst->id = src->id;
         switch (src->operation) {
         case BLKIF_OP_READ:
         case BLKIF_OP_WRITE:
         case BLKIF_OP_WRITE_BARRIER:
         case BLKIF_OP_FLUSH_DISKCACHE:
+                dst->u.rw.nr_segments = src->u.rw.nr_segments;
+                dst->u.rw.handle = src->u.rw.handle;
+                dst->u.rw.id = src->u.rw.id;
                 dst->u.rw.sector_number = src->u.rw.sector_number;
                 barrier();
-                if (n > dst->nr_segments)
-                        n = dst->nr_segments;
+                if (n > dst->u.rw.nr_segments)
+                        n = dst->u.rw.nr_segments;
                 for (i = 0; i < n; i++)
                         dst->u.rw.seg[i] = src->u.rw.seg[i];
                 break;