MINOR: stats-file: reserve some bytes in exported structs

We may need additional struct members in shm_stats_file_object and
shm_stats_file_hdr, yet since these structs are exported they should
not change in size nor ordering else it would require a version change
to break compability on purpose since mapping would differ.

Here we reserve 64 additional bytes in shm_stats_file_object, and
128 bytes in shm_stats_file_hdr for future usage.

diff --git a/include/haproxy/stats-file-t.h b/include/haproxy/stats-file-t.h
index 2ad7fafcbd70eb22b3d404fca1fa929800ae758a..03c65c3b489666af09a49e015a7e2057a7f941a8 100644 (file)
--- a/include/haproxy/stats-file-t.h
+++ b/include/haproxy/stats-file-t.h
@@ -21,7 +21,12 @@ enum stfile_domain {
                                              * sent heartbeat will be considered down
                                              */
 
-/* header for shm stats file ("shm-stats-file") */
+/* header for shm stats file ("shm-stats-file")
+ *
+ * exported struct:
+ * any change in size or ordering would represent breaking change and
+ * should cause a version change
+ */
 struct shm_stats_file_hdr {
        /* to check if the header is compatible with current haproxy version */
        struct {
@@ -46,11 +51,17 @@ struct shm_stats_file_hdr {
        } slots[64];
        int objects; /* actual number of objects stored in the shm */
        int objects_slots; /* total available objects slots unless map is resized */
+       ALWAYS_PAD(128); // reserve 128 bytes for future usage
 };
 
 #define SHM_STATS_FILE_OBJECT_TYPE_FE 0x0
 #define SHM_STATS_FILE_OBJECT_TYPE_BE 0x1
 
+/*
+ * exported struct:
+ * any change in size or ordering would represent breaking change and
+ * should cause a version change
+ */
 struct shm_stats_file_object {
        char guid[GUID_MAX_LEN + 1];
        uint8_t tgid; // thread group ID from 1 to 64
@@ -64,6 +75,7 @@ struct shm_stats_file_object {
                struct fe_counters_shared_tg fe;
                struct be_counters_shared_tg be;
        } data;
+       ALWAYS_PAD(64); // reserve 64 bytes for future usage
 };
 
 #define SHM_STATS_FILE_MAPPING_SIZE(obj) (sizeof(struct shm_stats_file_hdr) + (obj) * sizeof(struct shm_stats_file_object))