On Thu, Jun 08, 2023 at 09:17:38PM -0500, Eric Blake wrote:
> In order to more easily add a third reply type with an even larger
> header, but where the payload will look the same for both structured
> and extended replies, it is nicer if simple and structured replies are
> nested inside the same layer of sbuf.reply.hdr. Doing this also lets
> us add an alias for accessing the cookie directly without picking
> which header type we have on hand.
>
[...]
>
> Although we do not use union payload with simple replies, a later
> patch does use payload for two out of the three possible headers, and
> it does not hurt for sbuf to call out storage for more than we use on
> a particular state machine sequence. The commit is largely
> mechanical, and there should be no semantic change.
>
> Signed-off-by: Eric Blake <ebl...@redhat.com>
> ---
> lib/internal.h | 16 +++++--
> generator/states-reply.c | 35 +++++++-------
> generator/states-reply-chunk.c | 84 ++++++++++++++++-----------------
> generator/states-reply-simple.c | 4 +-
> 4 files changed, 76 insertions(+), 63 deletions(-)
Here's what I'm leaning towards squashing in, now that patch 2/4
landed as 2e34ceb8.
diff --git a/generator/states-reply.c b/generator/states-reply.c
index af5f6135..0d200513 100644
--- a/generator/states-reply.c
+++ b/generator/states-reply.c
@@ -19,6 +19,11 @@
#include <assert.h>
#include <stddef.h>
+#define ASSERT_MEMBER_ALIAS(type, member_a, member_b) \
+ STATIC_ASSERT (offsetof (type, member_a) == offsetof (type, member_b) && \
+ sizeof ((type *)NULL)->member_a == \
+ sizeof ((type *)NULL)->member_b, member_alias)
+
/* State machine for receiving reply messages from the server.
*
* Note that we never block while in this sub-group. If there is
@@ -70,12 +75,10 @@ REPLY.START:
* structs (an intentional design decision in the NBD spec when
* structured replies were added).
*/
- STATIC_ASSERT (offsetof (union reply_header, simple.cookie) ==
- offsetof (union reply_header, cookie),
- _cookie_aliasing_simple);
- STATIC_ASSERT (offsetof (union reply_header, structured.cookie) ==
- offsetof (union reply_header, cookie),
- _cookie_aliasing_structured);
+ ASSERT_MEMBER_ALIAS (union reply_header, simple.magic, magic);
+ ASSERT_MEMBER_ALIAS (union reply_header, simple.cookie, cookie);
+ ASSERT_MEMBER_ALIAS (union reply_header, structured.magic, magic);
+ ASSERT_MEMBER_ALIAS (union reply_header, structured.cookie, cookie);
assert (h->reply_cmd == NULL);
assert (h->rlen == 0);
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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