Fix: relayd comm: improperly packed rotate streams command header

[lttng-tools.git] / src / common / sessiond-comm / relayd.h

diff --git a/src/common/sessiond-comm/relayd.h b/src/common/sessiond-comm/relayd.h
index fe7d2936d869a0f03dcc82078b005d3592cdbd90..36a91070cbfd0cf6a587d238f6712912b9b78de0 100644 (file)
--- a/src/common/sessiond-comm/relayd.h
+++ b/src/common/sessiond-comm/relayd.h
@@ -239,17 +239,70 @@ struct lttcomm_relayd_stream_rotation_position {
        uint64_t rotate_at_seq_num;
 } LTTNG_PACKED;
 
+/*
+ * For certain releases, the LTTNG_PACKED annotation was missing on the
+ * `new_chunk_id` field which causes padding to be added between the
+ * "optional" structure's `is_set` and `value` fields.
+ *
+ * Three alignment cases are handled:
+ *   - `value` is aligned to the next byte boundary after `is_set`
+ *     no padding is produced, see
+ *     `struct lttcomm_relayd_rotate_streams_packed`,
+ *   - `value` is aligned to the next 4-byte boundary after `is_set`
+ *     (e.g. x86), 3 bytes of padding are produced, see
+ *     `struct lttcomm_relayd_rotate_streams_3_bytes_padding`,
+ *   - `value` is aligned to the next 8-byte boundary after `is_set`
+ *     (e.g. x86-64), 7 bytes of padding are produced, see
+ *     `struct lttcomm_relayd_rotate_streams_7_bytes_padding`.
+ *
+ * Note that since this structure's advertised size is used to determine
+ * the size of the padding it includes, it can't be extended with new
+ * optional fields. A new command would be needed.
+ */
 struct lttcomm_relayd_rotate_streams {
        uint32_t stream_count;
        /*
         * Streams can be rotated outside of a chunk but not be parented to
         * a new chunk.
+        *
+        * Improperly packed, but left as-is for backwards compatibility
+        * with unpatched relay daemons.
         */
        LTTNG_OPTIONAL_COMM(uint64_t) new_chunk_id;
        /* `stream_count` positions follow. */
        struct lttcomm_relayd_stream_rotation_position rotation_positions[];
 } LTTNG_PACKED;
 
+struct lttcomm_relayd_rotate_streams_packed {
+       uint32_t stream_count;
+       LTTNG_OPTIONAL_COMM(uint64_t) LTTNG_PACKED new_chunk_id;
+       struct lttcomm_relayd_stream_rotation_position rotation_positions[];
+} LTTNG_PACKED;
+
+struct lttcomm_relayd_rotate_streams_3_bytes_padding {
+       uint32_t stream_count;
+       struct {
+               union {
+                       uint8_t is_set;
+                       uint32_t padding;
+               };
+               uint64_t value;
+       } LTTNG_PACKED new_chunk_id;
+       struct lttcomm_relayd_stream_rotation_position rotation_positions[];
+} LTTNG_PACKED;
+
+struct lttcomm_relayd_rotate_streams_7_bytes_padding {
+       uint32_t stream_count;
+       struct {
+               union {
+                       uint8_t is_set;
+                       uint64_t padding;
+               };
+               uint64_t value;
+       } LTTNG_PACKED new_chunk_id;
+       struct lttcomm_relayd_stream_rotation_position rotation_positions[];
+} LTTNG_PACKED;
+
 struct lttcomm_relayd_create_trace_chunk {
        uint64_t chunk_id;
        /* Seconds since EPOCH. */