Because trace_opt_parse always deletes the options it has parsed,
trace_init_file's call to qemu_find_opts_singleton always
creates an empty -trace option group.  Therefore, the subsequent
qemu_opt_get(opts, "file") always returns NULL.

To fix this, save the last "-trace file=..." option in a global
variable and use it later in trace_init_file.

This is similar to what was done before commit 92eecfff32 ("trace:
remove argument from trace_init_file", 2020-11-11), except contained
within trace/control.c and without memory leaks.

Fixes: 92eecfff32 ("trace: remove argument from trace_init_file", 2020-11-11)
Cc: stefanha@redhat.com
Reported-by: armbru@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210209145759.141231-2-pbonzini@redhat.com>
---
 trace/control.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/trace/control.c b/trace/control.c
index cd04dd4e0c..4be38e1af2 100644
--- a/trace/control.c
+++ b/trace/control.c
@@ -40,6 +40,7 @@ static size_t nevent_groups;
 static uint32_t next_id;
 static uint32_t next_vcpu_id;
 static bool init_trace_on_startup;
+static char *trace_opts_file;
 
 QemuOptsList qemu_trace_opts = {
     .name = "trace",
@@ -224,10 +225,8 @@ static void trace_init_events(const char *fname)
 
 void trace_init_file(void)
 {
-    QemuOpts *opts = qemu_find_opts_singleton("trace");
-    const char *file = qemu_opt_get(opts, "file");
 #ifdef CONFIG_TRACE_SIMPLE
-    st_set_trace_file(file);
+    st_set_trace_file(trace_opts_file);
     if (init_trace_on_startup) {
         st_set_trace_file_enabled(true);
     }
@@ -238,11 +237,11 @@ void trace_init_file(void)
      * backend. However we should only override -D if we actually have
      * something to override it with.
      */
-    if (file) {
-        qemu_set_log_filename(file, &error_fatal);
+    if (trace_opts_file) {
+        qemu_set_log_filename(trace_opts_file, &error_fatal);
     }
 #else
-    if (file) {
+    if (trace_opts_file) {
         fprintf(stderr, "error: --trace file=...: "
                 "option not supported by the selected tracing backends\n");
         exit(1);
@@ -303,6 +302,8 @@ void trace_opt_parse(const char *optarg)
     }
     trace_init_events(qemu_opt_get(opts, "events"));
     init_trace_on_startup = true;
+    g_free(trace_opts_file);
+    trace_opts_file = g_strdup(qemu_opt_get(opts, "file"));
     qemu_opts_del(opts);
 }
 
-- 
2.29.2