trace-cmd record: Fix top_instance.output_file being NULL

If the -o comes after a -B, the output_file name will be associated to the
trace instance of that -B, and the top_instance.output_file will be NULL.
If recording is started in a location that is read-only, the temp file
created for the top instance is going to try to be created in that read-only
file system.

 /sys/kernel/tracing# trace-cmd record -o /tmp/test.dat -B test -e sched
 Hit Ctrl^C to stop recording
 ^Ctrace-cmd: Permission denied
   could not create file (null).cpu0

Make sure all instances, including the top_instance has their output_file
correct.

Also, because the output file could have been created under another
instance, check if that instance already has the output file before
assigning over it.

Link: https://lore.kernel.org/linux-trace-devel/20240119162743.1a107fa9@gandalf.local.home

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 762afba4..91cc90d4 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -7122,6 +7122,10 @@ static void record_trace(int argc, char **argv,
 	if (!ctx->output)
 		ctx->output = DEFAULT_INPUT_FILE;
 
+	/* Make sure top_instance.output_file exists */
+	if (!top_instance.output_file)
+		top_instance.output_file = strdup(ctx->output);
+
 	if (ctx->data_flags & (DATA_FL_GUEST | DATA_FL_PROXY))
 		set_tsync_params(ctx);
 
@@ -7131,7 +7135,9 @@ static void record_trace(int argc, char **argv,
 	for_all_instances(instance) {
 		if (ctx->temp)
 			instance->temp_dir = ctx->temp;
-		instance->output_file = strdup(ctx->output);
+		/* The -o could have been done after -B */
+		if (!instance->output_file)
+			instance->output_file = strdup(ctx->output);
 		if (!instance->output_file)
 			die("Failed to allocate output file name for instance");
 		if (!ctx->manual && instance->flags & BUFFER_FL_PROFILE)