From 71d3169070a4c9e0df87a9d825dd7520022385a7 Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 8 May 2013 14:52:42 -0400
Subject: [PATCH] Fix: add provider ABI compatibility check

There is not much we can do for this compatibility bug in lttng-ust 2.0
and 2.1 (already stable). Adding this check so that starting with
lttng-ust 2.2, when liblttng-ust encounters a probe provider with a
provider version major number higher than it supports, it will reject
it.

Fixes #502

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 include/lttng/ust-events.h           | 13 ++++++++-
 include/lttng/ust-tracepoint-event.h |  2 ++
 liblttng-ust/lttng-probes.c          | 40 ++++++++++++++++++++++++++++
 3 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h
index 749478a6..0b8664c3 100644
--- a/include/lttng/ust-events.h
+++ b/include/lttng/ust-events.h
@@ -37,6 +37,15 @@
 
 #define LTTNG_UST_UUID_LEN		16
 
+/*
+ * Tracepoint provider version. Compatibility based on the major number.
+ * Older tracepoint providers can always register to newer lttng-ust
+ * library, but the opposite is rejected: a newer tracepoint provider is
+ * rejected by an older lttng-ust library.
+ */
+#define LTTNG_UST_PROVIDER_MAJOR	1
+#define LTTNG_UST_PROVIDER_MINOR	0
+
 struct lttng_channel;
 struct lttng_session;
 struct lttng_ust_lib_ring_buffer_ctx;
@@ -251,7 +260,7 @@ struct lttng_event_desc {
 	} u;
 };
 
-#define LTTNG_UST_PROBE_DESC_PADDING	20
+#define LTTNG_UST_PROBE_DESC_PADDING	12
 struct lttng_probe_desc {
 	const char *provider;
 	const struct lttng_event_desc **event_desc;
@@ -259,6 +268,8 @@ struct lttng_probe_desc {
 	struct cds_list_head head;		/* chain registered probes */
 	struct cds_list_head lazy_init_head;
 	int lazy;				/* lazy registration */
+	uint32_t major;
+	uint32_t minor;
 	char padding[LTTNG_UST_PROBE_DESC_PADDING];
 };
 
diff --git a/include/lttng/ust-tracepoint-event.h b/include/lttng/ust-tracepoint-event.h
index e46cc1a1..c7bceef6 100644
--- a/include/lttng/ust-tracepoint-event.h
+++ b/include/lttng/ust-tracepoint-event.h
@@ -652,6 +652,8 @@ static struct lttng_probe_desc _TP_COMBINE_TOKENS(__probe_desc___, TRACEPOINT_PR
 	.provider = __tp_stringify(TRACEPOINT_PROVIDER),
 	.event_desc = _TP_COMBINE_TOKENS(__event_desc___, TRACEPOINT_PROVIDER),
 	.nr_events = _TP_ARRAY_SIZE(_TP_COMBINE_TOKENS(__event_desc___, TRACEPOINT_PROVIDER)),
+	.major = LTTNG_UST_PROVIDER_MAJOR,
+	.minor = LTTNG_UST_PROVIDER_MINOR,
 };
 
 /*
diff --git a/liblttng-ust/lttng-probes.c b/liblttng-ust/lttng-probes.c
index f028ccab..433171cf 100644
--- a/liblttng-ust/lttng-probes.c
+++ b/liblttng-ust/lttng-probes.c
@@ -160,10 +160,47 @@ const struct lttng_probe_desc *find_provider(const char *provider)
 	return NULL;
 }
 
+static
+int check_provider_version(struct lttng_probe_desc *desc)
+{
+	/*
+	 * Check tracepoint provider version compatibility.
+	 */
+	if (desc->major <= LTTNG_UST_PROVIDER_MAJOR) {
+		DBG("Provider \"%s\" accepted, version %u.%u is compatible "
+			"with LTTng UST provider version %u.%u.",
+			desc->provider, desc->major, desc->minor,
+			LTTNG_UST_PROVIDER_MAJOR,
+			LTTNG_UST_PROVIDER_MINOR);
+		if (desc->major < LTTNG_UST_PROVIDER_MAJOR) {
+			DBG("However, some LTTng UST features might not be "
+				"available for this provider unless it is "
+				"recompiled against a more recent LTTng UST.");
+		}
+		return 1;		/* accept */
+	} else {
+		ERR("Provider \"%s\" rejected, version %u.%u is incompatible "
+			"with LTTng UST provider version %u.%u. Please upgrade "
+			"LTTng UST.",
+			desc->provider, desc->major, desc->minor,
+			LTTNG_UST_PROVIDER_MAJOR,
+			LTTNG_UST_PROVIDER_MINOR);
+		return 0;		/* reject */
+	}
+}
+
+
 int lttng_probe_register(struct lttng_probe_desc *desc)
 {
 	int ret = 0;
 
+	/*
+	 * If version mismatch, don't register, but don't trigger assert
+	 * on caller. The version check just prints an error.
+	 */
+	if (!check_provider_version(desc))
+		return 0;
+
 	ust_lock();
 
 	/*
@@ -197,6 +234,9 @@ int ltt_probe_register(struct lttng_probe_desc *desc)
 
 void lttng_probe_unregister(struct lttng_probe_desc *desc)
 {
+	if (!check_provider_version(desc))
+		return;
+
 	ust_lock();
 	if (!desc->lazy)
 		cds_list_del(&desc->head);
-- 
2.34.1