gpg: Don't take the a TOFU trust model from the trustdb,

* g10/tdbio.c (tdbio_update_version_record): Never store a TOFU model.
(create_version_record): Don't init as TOFU.
(tdbio_db_matches_options): Don't indicate a change in case TOFU is
stored in an old trustdb file.
--

This change allows to switch between a tofu and pgp or tofu+pgp trust
model without an auto rebuild of the trustdb.  This also requires that
the tofu trust model is requested on the command line.  If TOFU will
ever be the default we need to tweak the model detection via TM_AUTO
by also looking into the TOFU data base,

GnuPG-bug-id: 4134

doc/gpg.texi

@@ -1724,7 +1724,8 @@ Set what trust model GnuPG should follow. The models are:
   @opindex trust-model:auto
   Select the trust model depending on whatever the internal trust
   database says. This is the default model if such a database already
-  exists.
+  exists.  Note that a tofu trust model is not considered here and
+  must be enabled explicitly.
 @end table
 
 @item --auto-key-locate @var{mechanisms}

g10/tdbio.c

@@ -562,6 +562,12 @@ tdbio_update_version_record (ctrl_t ctrl)
 {
   TRUSTREC rec;
   int rc;
+  int opt_tm;
+
+  /* Never store a TOFU trust model in the trustdb.  Use PGP instead.  */
+  opt_tm = opt.trust_model;
+  if (opt_tm == TM_TOFU || opt_tm == TM_TOFU_PGP)
+    opt_tm = TM_PGP;
 
   memset (&rec, 0, sizeof rec);
 
@@ -572,7 +578,7 @@ tdbio_update_version_record (ctrl_t ctrl)
       rec.r.ver.marginals   = opt.marginals_needed;
       rec.r.ver.completes   = opt.completes_needed;
       rec.r.ver.cert_depth  = opt.max_cert_depth;
-      rec.r.ver.trust_model = opt.trust_model;
+      rec.r.ver.trust_model = opt_tm;
       rec.r.ver.min_cert_level = opt.min_cert_level;
       rc = tdbio_write_record (ctrl, &rec);
     }
@@ -591,6 +597,12 @@ create_version_record (ctrl_t ctrl)
 {
   TRUSTREC rec;
   int rc;
+  int opt_tm;
+
+  /* Never store a TOFU trust model in the trustdb.  Use PGP instead.  */
+  opt_tm = opt.trust_model;
+  if (opt_tm == TM_TOFU || opt_tm == TM_TOFU_PGP)
+    opt_tm = TM_PGP;
 
   memset (&rec, 0, sizeof rec);
   rec.r.ver.version     = 3;
@@ -598,8 +610,8 @@ create_version_record (ctrl_t ctrl)
   rec.r.ver.marginals   = opt.marginals_needed;
   rec.r.ver.completes   = opt.completes_needed;
   rec.r.ver.cert_depth  = opt.max_cert_depth;
-  if (opt.trust_model == TM_PGP || opt.trust_model == TM_CLASSIC)
+  if (opt_tm == TM_PGP || opt_tm == TM_CLASSIC)
-    rec.r.ver.trust_model = opt.trust_model;
+    rec.r.ver.trust_model = opt_tm;
   else
     rec.r.ver.trust_model = TM_PGP;
   rec.r.ver.min_cert_level = opt.min_cert_level;
@@ -883,16 +895,25 @@ tdbio_db_matches_options()
     {
       TRUSTREC vr;
       int rc;
+      int opt_tm, tm;
 
       rc = tdbio_read_record (0, &vr, RECTYPE_VER);
       if( rc )
 	log_fatal( _("%s: error reading version record: %s\n"),
 		   db_name, gpg_strerror (rc) );
 
+      /* Consider tofu and pgp the same.  */
+      tm = vr.r.ver.trust_model;
+      if (tm == TM_TOFU || tm == TM_TOFU_PGP)
+        tm = TM_PGP;
+      opt_tm  = opt.trust_model;
+      if (opt_tm == TM_TOFU || opt_tm == TM_TOFU_PGP)
+        opt_tm = TM_PGP;
+
       yes_no = vr.r.ver.marginals == opt.marginals_needed
 	&& vr.r.ver.completes == opt.completes_needed
 	&& vr.r.ver.cert_depth == opt.max_cert_depth
-	&& vr.r.ver.trust_model == opt.trust_model
+	&& tm == opt_tm
 	&& vr.r.ver.min_cert_level == opt.min_cert_level;
     }