[Spice-devel] [PATCH spice-protocol v2] stats: Avoid holes in SpiceStat structure

[Frediano Ziglio]

The SpiceStat structure can be 20 or 24 bytes depending on alignment.
Being a memory mapped structure potentially used with lockless access
is not good to have it unaligned.
The current tool that reads this memory mapped file (reds_stats) is
able to detect if the structure is either 20 or 24 bytes and act
according so changing this structure won't affect the behaviour
(unless you have an old tool but as they are usually packages together
is quite improbable).
This will also help on Windows as in that system is not possible for
reds_stats to implement the same discovery trick implemented on Linux
as on Windows is not possible to read the size of the file mapping
(on Windows to implement shared memory you can use a file mapping
not associated to a file).
The structure will change layout only on 32-bit which it's not that
recommended nowadays (64-bit platforms we support align 64-bit integer
to 64 bits).

Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
---
 spice/stats.h | 2 ++
 1 file changed, 2 insertions(+)

Changes since v1:
- update commit message and comment.

diff --git a/spice/stats.h b/spice/stats.h
index d4c45ab..44c6482 100644
--- a/spice/stats.h
+++ b/spice/stats.h
@@ -66,6 +66,8 @@ typedef struct SpiceStat {
     uint32_t generation;
     uint32_t num_of_nodes;
     uint32_t root_index;
+    /* to avoid holes in the structure on some platforms */
+    uint32_t padding;
     SpiceStatNode nodes[];
 } SpiceStat;
 
-- 
2.20.1