From 335a95b7e3fab0d66908594ac7039651c7aaf6f4 Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon, 30 Jan 2012 08:30:53 -0500
Subject: [PATCH] Add kernel work-around for boot_id

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lkml.org/lkml/2012/1/29/180
---
 src/bin/lttng-sessiond/kernel.c | 27 +++++++++++++++++++++++++++
 src/bin/lttng-sessiond/kernel.h |  2 ++
 src/bin/lttng-sessiond/main.c   |  2 ++
 3 files changed, 31 insertions(+)

diff --git a/src/bin/lttng-sessiond/kernel.c b/src/bin/lttng-sessiond/kernel.c
index d9e047fc3..43c628577 100644
--- a/src/bin/lttng-sessiond/kernel.c
+++ b/src/bin/lttng-sessiond/kernel.c
@@ -638,3 +638,30 @@ error_version:
 error:
 	return ret;
 }
+
+/*
+ * Kernel work-arounds called at the start of sessiond main().
+ */
+int init_kernel_workarounds(void)
+{
+	FILE *fp;
+
+	/*
+	 * boot_id needs to be read once before being used concurrently
+	 * to deal with a Linux kernel race. A fix is proposed for
+	 * upstream, but the work-around is needed for older kernels.
+	 */
+	fp = fopen("/proc/sys/kernel/random/boot_id", "r");
+	if (!fp) {
+		goto end_boot_id;
+	}
+	while (!feof(fp)) {
+		char buf[37] = "";
+
+		(void) fread(buf, 1, sizeof(buf), fp);
+	}
+	fclose(fp);
+end_boot_id:
+
+	return 0;
+}
diff --git a/src/bin/lttng-sessiond/kernel.h b/src/bin/lttng-sessiond/kernel.h
index a916f6841..d663dbb1c 100644
--- a/src/bin/lttng-sessiond/kernel.h
+++ b/src/bin/lttng-sessiond/kernel.h
@@ -55,4 +55,6 @@ void kernel_wait_quiescent(int fd);
 int kernel_calibrate(int fd, struct lttng_kernel_calibrate *calibrate);
 int kernel_validate_version(int tracer_fd);
 
+int init_kernel_workarounds(void);
+
 #endif /* _LTT_KERNEL_CTL_H */
diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index 631aa6b2d..9b2d1fe00 100644
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -4158,6 +4158,8 @@ int main(int argc, char **argv)
 	void *status;
 	const char *home_path;
 
+	init_kernel_workarounds();
+
 	rcu_register_thread();
 
 	/* Create thread quit pipe */
-- 
2.34.1