From 7802bae326824ecb116cb0d782bb7472eaa6f6e4 Mon Sep 17 00:00:00 2001
From: Liguang Li <liguang.li@windriver.com>
Date: Mon, 28 Nov 2016 16:37:47 +0800
Subject: [PATCH] Fix: truncate the metadata file in shm-path
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In the shm-path mode, the metadata will be backuped to a metadata
file, when run the lttng command "lttng metadata regenerate" to
resample the wall time following a major NTP correction, the metadata
file will not be truncated and regenerated.

Add the function clear_metadata_file() to truncate and regenerate the
metadata file.

Signed-off-by: Liguang Li <liguang.li@windriver.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---
 src/bin/lttng-sessiond/cmd.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/src/bin/lttng-sessiond/cmd.c b/src/bin/lttng-sessiond/cmd.c
index 325ffd2cf..cc81906b6 100644
--- a/src/bin/lttng-sessiond/cmd.c
+++ b/src/bin/lttng-sessiond/cmd.c
@@ -3377,6 +3377,27 @@ end:
 	return ret;
 }
 
+static
+int clear_metadata_file(int fd)
+{
+	int ret;
+
+	ret = lseek(fd, 0, SEEK_SET);
+	if (ret < 0) {
+		PERROR("lseek");
+		goto end;
+	}
+
+	ret = ftruncate(fd, 0);
+	if (ret < 0) {
+		PERROR("ftruncate");
+		goto end;
+	}
+
+end:
+	return ret;
+}
+
 static
 int ust_regenerate_metadata(struct ltt_ust_session *usess)
 {
@@ -3398,6 +3419,15 @@ int ust_regenerate_metadata(struct ltt_ust_session *usess)
 		memset(registry->metadata, 0, registry->metadata_alloc_len);
 		registry->metadata_len = 0;
 		registry->metadata_version++;
+		if (registry->metadata_fd > 0) {
+			/* Clear the metadata file's content. */
+			ret = clear_metadata_file(registry->metadata_fd);
+			if (ret) {
+				pthread_mutex_unlock(&registry->lock);
+				goto end;
+			}
+		}
+
 		ret = ust_metadata_session_statedump(registry, NULL,
 				registry->major, registry->minor);
 		if (ret) {
-- 
2.34.1