From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 16 Mar 2021 02:50:28 +0000 (-0400)
Subject: Refactoring: struct lttng_channel_ops
X-Git-Tag: v2.13.0-rc1~289
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=49926dbd13cfcb46f6947b7e99bc2999c06dc743;p=lttng-ust.git

Refactoring: struct lttng_channel_ops

- Namespace this structure with lttng_ust_ prefix,
- Use struct_size extensibility scheme. There was no prior padding, so
  extensibility was an issue in the past.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ie8334f5f651f100aaea60ee83d3c8e2b6b300a5a
---

diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h
index 164c82c4..d070a3cc 100644
--- a/include/lttng/ust-events.h
+++ b/include/lttng/ust-events.h
@@ -498,8 +498,14 @@ struct lttng_ust_shm_handle;
  * IMPORTANT: this structure is part of the ABI between the probe and
  * UST. Fields need to be only added at the end, never reordered, never
  * removed.
+ *
+ * The field @struct_size should be used to determine the size of the
+ * structure. It should be queried before using additional fields added
+ * at the end of the structure.
  */
-struct lttng_channel_ops {
+struct lttng_ust_channel_ops {
+	uint32_t struct_size;
+
 	struct lttng_channel *(*channel_create)(const char *name,
 			void *buf_addr,
 			size_t subbuf_size, size_t num_subbuf,
@@ -527,6 +533,8 @@ struct lttng_channel_ops {
 	int (*flush_buffer)(struct channel *chan, struct lttng_ust_shm_handle *handle);
 	void (*event_strcpy)(struct lttng_ust_lib_ring_buffer_ctx *ctx,
 			const char *src, size_t len);
+
+	/* End of base ABI. Fields below should be used after checking struct_size. */
 };
 
 /*
@@ -548,7 +556,7 @@ struct lttng_channel {
 	struct lttng_session *session;
 	int objd;			/* Object associated to channel */
 	struct cds_list_head node;	/* Channel list in session */
-	const struct lttng_channel_ops *ops;
+	const struct lttng_ust_channel_ops *ops;
 	int header_type;		/* 0: unset, 1: compact, 2: large */
 	struct lttng_ust_shm_handle *handle;	/* shared-memory handle */
 
diff --git a/liblttng-ust/lttng-ring-buffer-client.h b/liblttng-ust/lttng-ring-buffer-client.h
index 9cc862cf..c3b77182 100644
--- a/liblttng-ust/lttng-ring-buffer-client.h
+++ b/liblttng-ust/lttng-ring-buffer-client.h
@@ -792,6 +792,7 @@ int lttng_flush_buffer(struct channel *chan, struct lttng_ust_shm_handle *handle
 static struct lttng_transport lttng_relay_transport = {
 	.name = "relay-" RING_BUFFER_MODE_TEMPLATE_STRING "-mmap",
 	.ops = {
+		.struct_size = sizeof(struct lttng_ust_channel_ops),
 		.channel_create = _channel_create,
 		.channel_destroy = lttng_channel_destroy,
 		.event_reserve = lttng_event_reserve,
diff --git a/liblttng-ust/lttng-ring-buffer-metadata-client.h b/liblttng-ust/lttng-ring-buffer-metadata-client.h
index 5a3840c8..bb5c5dfe 100644
--- a/liblttng-ust/lttng-ring-buffer-metadata-client.h
+++ b/liblttng-ust/lttng-ring-buffer-metadata-client.h
@@ -314,14 +314,14 @@ int lttng_flush_buffer(struct channel *chan, struct lttng_ust_shm_handle *handle
 static struct lttng_transport lttng_relay_transport = {
 	.name = "relay-" RING_BUFFER_MODE_TEMPLATE_STRING "-mmap",
 	.ops = {
+		.struct_size = sizeof(struct lttng_ust_channel_ops),
+
 		.channel_create = _channel_create,
 		.channel_destroy = lttng_channel_destroy,
 		.event_reserve = lttng_event_reserve,
 		.event_commit = lttng_event_commit,
 		.event_write = lttng_event_write,
 		.packet_avail_size = lttng_packet_avail_size,
-		//.get_reader_wait_queue = lttng_get_reader_wait_queue,
-		//.get_hp_wait_queue = lttng_get_hp_wait_queue,
 		.is_finalized = lttng_is_finalized,
 		.is_disabled = lttng_is_disabled,
 		.flush_buffer = lttng_flush_buffer,
diff --git a/liblttng-ust/ust-events-internal.h b/liblttng-ust/ust-events-internal.h
index f351e954..a3146b37 100644
--- a/liblttng-ust/ust-events-internal.h
+++ b/liblttng-ust/ust-events-internal.h
@@ -189,7 +189,7 @@ struct lttng_event_notifier_group {
 struct lttng_transport {
 	char *name;
 	struct cds_list_head node;
-	struct lttng_channel_ops ops;
+	struct lttng_ust_channel_ops ops;
 	const struct lttng_ust_lib_ring_buffer_config *client_config;
 };