[Qemu-devel] [PATCH v6 02/20] block: Drop private ioctl-only members of BlockRequest

[Eric Blake <eblake@redhat.com>]

I was thrown by the fact that the public type BlockRequest had
an anonymous union, but no obvious discriminator.  Turns out
that the only client of the second branch of the union was code
internal to io.c, and that with a slight abuse of QEMUIOVector*
to pass a void* pointer, we can make the public interface less
confusing.

(Yes, I know that strict C doesn't guarantee that you can cast
void* to the wrong type and then back to void* - it only
guarantees the reverse direction of the original pointer to
void* and back to the original type - but we already have other
assumptions throughout the qemu code base that assume that all
pointers are interchangeable in representation).

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 include/block/block.h | 16 ++++------------
 block/io.c            |  8 +++++---
 2 files changed, 9 insertions(+), 15 deletions(-)

diff --git a/include/block/block.h b/include/block/block.h
index 0e8b4d1..754aae3 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -334,18 +334,10 @@ void bdrv_aio_cancel_async(BlockAIOCB *acb);

 typedef struct BlockRequest {
     /* Fields to be filled by multiwrite caller */
-    union {
-        struct {
-            int64_t sector;
-            int nb_sectors;
-            int flags;
-            QEMUIOVector *qiov;
-        };
-        struct {
-            int req;
-            void *buf;
-        };
-    };
+    int64_t sector;
+    int nb_sectors;
+    int flags;
+    QEMUIOVector *qiov;
     BlockCompletionFunc *cb;
     void *opaque;

diff --git a/block/io.c b/block/io.c
index 0db1146..f15c0f4 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2614,7 +2614,7 @@ static void coroutine_fn bdrv_co_aio_ioctl_entry(void *opaque)
 {
     BlockAIOCBCoroutine *acb = opaque;
     acb->req.error = bdrv_co_do_ioctl(acb->common.bs,
-                                      acb->req.req, acb->req.buf);
+                                      acb->req.flags, acb->req.qiov);
     bdrv_co_complete(acb);
 }

@@ -2628,8 +2628,10 @@ BlockAIOCB *bdrv_aio_ioctl(BlockDriverState *bs,

     acb->need_bh = true;
     acb->req.error = -EINPROGRESS;
-    acb->req.req = req;
-    acb->req.buf = buf;
+    /* Slight type abuse here, so we don't have to expose extra fields
+     * in the public struct BlockRequest */
+    acb->req.flags = req;
+    acb->req.qiov = buf;
     co = qemu_coroutine_create(bdrv_co_aio_ioctl_entry);
     qemu_coroutine_enter(co, acb);

-- 
2.5.5