virgl: Add tracing to stderr as alternative tracing method

This simply logs all tagged calls and scopes to stderr.

v2: - Fix option comparsion
    - add trace_init stub
    - update the combo option description

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>

meson.build

@@ -96,6 +96,10 @@ if with_tracing == 'perfetto'
    conf_data.set('ENABLE_TRACING', 'TRACE_WITH_PERFETTO')
 endif
 
+if with_tracing == 'stderr'
+   conf_data.set('ENABLE_TRACING', 'TRACE_WITH_STDERR')
+endif
+
 if cc.has_header('sys/uio.h')
    conf_data.set('HAVE_SYS_UIO_H', 1)
 endif

meson_options.txt

@@ -63,6 +63,6 @@ option(
   'tracing',
   type : 'combo',
   value : 'none',
-  choices : [ 'perfetto', 'none' ],
-  description : 'enable emitting traces for Perfetto'
+  choices : [ 'perfetto', 'stderr', 'none' ],
+  description : 'enable emitting traces using the selected backend'
 )

src/virgl_util.c

@@ -47,6 +47,10 @@
 #include <vperfetto-min.h>
 #endif
 
+#if ENABLE_TRACING == TRACE_WITH_STDERR
+#include <stdio.h>
+#endif
+
 unsigned hash_func_u32(void *key)
 {
    intptr_t ip = pointer_to_intptr(key);
@@ -139,3 +143,40 @@ void trace_end(char **dummy)
    vperfetto_min_endTrackEvent_VMM();
 }
 #endif
+
+#if ENABLE_TRACING == TRACE_WITH_STDERR
+static int nesting_depth = 0;
+void trace_init(void)
+{
+}
+
+char *trace_begin(const char* format, ...)
+{
+   for (int i = 0; i < nesting_depth; ++i)
+      fprintf(stderr, "  ");
+
+   fprintf(stderr, "ENTER:");
+   char *buffer;
+   va_list args;
+   va_start (args, format);
+   int size = vasprintf(&buffer, format, args);
+
+   if (size < 0)
+      buffer=strdup("error");
+
+   va_end (args);
+   fprintf(stderr, "%s\n", buffer);
+   nesting_depth++;
+
+   return buffer;
+}
+
+void trace_end(char **func_name)
+{
+   --nesting_depth;
+   for (int i = 0; i < nesting_depth; ++i)
+      fprintf(stderr, "  ");
+   fprintf(stderr, "LEAVE %s\n", *func_name);
+   free(*func_name);
+}
+#endif

src/virgl_util.h

@@ -33,7 +33,7 @@
 #endif
 
 #define TRACE_WITH_PERFETTO 1
-
+#define TRACE_WITH_STDERR 2
 
 #define BIT(n)                   (UINT32_C(1) << (n))