tpm: Make tss2 log into /dev/null

There is no way yet[1] to control how much tss2 logs and to where, from the C
API. The problem with that is if there is no TPM 2.0 module, it'll very
verbosely tell about it via ERROR and WARNING log entries directly to
stderr, which isn't really what we want.

Change this by setting the env var controlling the log target to
/dev/null unless the tpm debug key is enabled.

[1] tpm2-software/tpm2-tss#2087

src/grd-debug.c

@@ -26,6 +26,7 @@
 
 static const GDebugKey grd_debug_keys[] = {
   { "vnc", GRD_DEBUG_VNC },
+  { "tpm", GRD_DEBUG_TPM },
 };
 
 static GrdDebugFlags debug_flags;

src/grd-debug.h

@@ -25,6 +25,7 @@ typedef enum _GrdDebugFlags
 {
   GRD_DEBUG_NONE = 0,
   GRD_DEBUG_VNC = 1 << 0,
+  GRD_DEBUG_TPM = 1 << 1,
 } GrdDebugFlags;
 
 GrdDebugFlags grd_get_debug_flags (void);

src/grd-tpm.c

@@ -32,6 +32,8 @@ G_GNUC_BEGIN_IGNORE_DEPRECATIONS
 #include <tss2_tctildr.h>
 G_GNUC_END_IGNORE_DEPRECATIONS
 
+#include "grd-debug.h"
+
 struct _GrdTpm
 {
   GObject parent;
@@ -722,6 +724,9 @@ grd_tpm_new (GrdTpmMode   mode,
 
   tpm = g_object_new (GRD_TYPE_TPM, NULL);
 
+  if (!(grd_get_debug_flags () & GRD_DEBUG_TPM))
+    g_setenv ("TSS2_LOGFILE", "/dev/null", TRUE);
+
   if (!init_transmission_interface (tpm, error))
     return NULL;
 

src/meson.build

@@ -176,6 +176,8 @@ control_sources = ([
 
 ctl_sources = ([
   'grd-ctl.c',
+  'grd-debug.c',
+  'grd-debug.h',
   credentials_sources,
 ])
 

tests/meson.build

@@ -72,6 +72,8 @@ tpm_test = executable(
   'tpm-test',
   sources: [
     'tpm-test.c',
+    '../src/grd-debug.c',
+    '../src/grd-debug.h',
     '../src/grd-tpm.c',
     '../src/grd-tpm.h',
   ],