New API: set-backend-settings, get-backend-settings.

Allow settings (an arbitrary list of strings) to be passed to the
current backend.  This will allow us to tweak how the backend works,
eg. by forcing TCG.

fish/guestfish.pod

@@ -1413,6 +1413,11 @@ This is the old way to set C<LIBGUESTFS_BACKEND>.
 Choose the default way to create the appliance.  See
 L<guestfs(3)/guestfs_set_backend>.
 
+=item LIBGUESTFS_BACKEND_SETTINGS
+
+A colon-separated list of backend-specific settings.
+See L<guestfs(3)/BACKEND>, L<guestfs(3)/BACKEND SETTINGS>.
+
 =item LIBGUESTFS_CACHEDIR
 
 The location where libguestfs will cache its appliance, when

generator/actions.ml

@@ -3060,6 +3060,39 @@ If you set the data threshold to unlimited (C<0>) then this call
 can read a journal entry of any size, ie. it is not limited by
 the libguestfs protocol." };
 
+  { defaults with
+    name = "set_backend_settings";
+    style = RErr, [StringList "settings"], [];
+    config_only = true;
+    blocking = false;
+    shortdesc = "set per-backend settings";
+    longdesc = "\
+Set a list of zero or more settings which are passed through to
+the current backend.  Each setting is a string which is interpreted
+in a backend-specific way, or ignored if not understood by the
+backend.
+
+The default value is an empty list, unless the environment
+variable C<LIBGUESTFS_BACKEND_SETTINGS> was set when the handle
+was created.  This environment variable contains a colon-separated
+list of settings.
+
+See L<guestfs(3)/BACKEND>, L<guestfs(3)/BACKEND SETTINGS>." };
+
+  { defaults with
+    name = "get_backend_settings";
+    style = RStringList "settings", [], [];
+    blocking = false;
+    tests = [
+      InitNone, Always, TestRun (
+        [["get_backend_settings"]]), []
+    ];
+    shortdesc = "get per-backend settings";
+    longdesc = "\
+Return the current backend settings.
+
+See L<guestfs(3)/BACKEND>, L<guestfs(3)/BACKEND SETTINGS>." };
+
 ]
 
 (* daemon_functions are any functions which cause some action

src/guestfs-internal-all.h

@@ -46,6 +46,7 @@
 #define STRNEQLEN(a,b,n) (strncmp((a),(b),(n)) != 0)
 #define STRCASENEQLEN(a,b,n) (strncasecmp((a),(b),(n)) != 0)
 #define STRPREFIX(a,b) (strncmp((a),(b),strlen((b))) == 0)
+#define STRCASEPREFIX(a,b) (strncasecmp((a),(b),strlen((b))) == 0)
 #define STRSUFFIX(a,b) (strlen((a)) >= strlen((b)) && STREQ((a)+strlen((a))-strlen((b)),(b)))
 
 #ifndef SOCK_CLOEXEC

src/guestfs-internal.h

@@ -407,6 +407,7 @@ struct guestfs_h
   char *backend_arg;            /* Pointer to the argument part. */
   const struct backend_ops *backend_ops;
   void *backend_data;           /* Per-handle data. */
+  char **backend_settings;      /* Backend settings (can be NULL). */
 
   /**** Runtime information. ****/
   char *last_error;             /* Last error on handle. */
@@ -724,6 +725,8 @@ extern char *guestfs___appliance_command_line (guestfs_h *g, const char *applian
 #define APPLIANCE_COMMAND_LINE_IS_TCG 1
 extern void guestfs___register_backend (const char *name, const struct backend_ops *);
 extern int guestfs___set_backend (guestfs_h *g, const char *method);
+extern const char *guestfs___get_backend_setting (guestfs_h *g, const char *name);
+extern int guestfs___get_backend_setting_bool (guestfs_h *g, const char *name);
 
 /* inspect.c */
 extern void guestfs___free_inspect_info (guestfs_h *g);

src/guestfs.pod

@@ -1483,6 +1483,13 @@ backend, do:
  unset LIBGUESTFS_BACKEND
  guestfish get-backend
 
+=head2 BACKEND SETTINGS
+
+Each backend can be configured by passing a list of strings.  You can
+either call L</guestfs_set_backend_settings> with a list of strings,
+or set the C<LIBGUESTFS_BACKEND_SETTINGS> environment variable to a
+colon-separated list of strings (before creating the handle).
+
 =head2 ATTACHING TO RUNNING DAEMONS
 
 I<Note (1):> This is B<highly experimental> and has a tendency to eat
@@ -4613,6 +4620,11 @@ This is the old way to set C<LIBGUESTFS_BACKEND>.
 Choose the default way to create the appliance.  See
 L</guestfs_set_backend> and L</BACKEND>.
 
+=item LIBGUESTFS_BACKEND_SETTINGS
+
+A colon-separated list of backend-specific settings.
+See L</BACKEND>, L</BACKEND SETTINGS>.
+
 =item LIBGUESTFS_CACHEDIR
 
 The location where libguestfs will cache its appliance, when

src/handle.c

@@ -245,6 +245,19 @@ parse_environment (guestfs_h *g,
     }
   }
 
+  str = do_getenv (data, "LIBGUESTFS_BACKEND_SETTINGS");
+  if (str && STRNEQ (str, "")) {
+    CLEANUP_FREE_STRING_LIST char **settings = guestfs___split_string (':', str);
+
+    if (settings == NULL) {
+      perrorf (g, "split_string: malloc");
+      return -1;
+    }
+
+    if (guestfs_set_backend_settings (g, settings) == -1)
+      return -1;
+  }
+
   return 0;
 }
 
@@ -673,6 +686,42 @@ guestfs__get_attach_method (guestfs_h *g)
   return guestfs_get_backend (g);
 }
 
+int
+guestfs__set_backend_settings (guestfs_h *g, char *const *settings)
+{
+  char **copy;
+
+  copy = guestfs___copy_string_list (settings);
+  if (copy == NULL) {
+    perrorf (g, "copy: malloc");
+    return -1;
+  }
+
+  guestfs___free_string_list (g->backend_settings);
+  g->backend_settings = copy;
+
+  return 0;
+}
+
+char **
+guestfs__get_backend_settings (guestfs_h *g)
+{
+  char *empty_list[1] = { NULL };
+  char **ret;
+
+  if (g->backend_settings == NULL)
+    ret = guestfs___copy_string_list (empty_list);
+  else
+    ret = guestfs___copy_string_list (g->backend_settings);
+
+  if (ret == NULL) {
+    perrorf (g, "copy: malloc");
+    return NULL;
+  }
+
+  return ret;                   /* caller frees */
+}
+
 int
 guestfs__set_pgroup (guestfs_h *g, int v)
 {

src/launch.c

@@ -481,3 +481,51 @@ guestfs___set_backend (guestfs_h *g, const char *method)
 
   return 0;
 }
+
+/* Convenience functions for backends to read settings. */
+
+/* Return the string value of a setting, or NULL if not set. */
+const char *
+guestfs___get_backend_setting (guestfs_h *g, const char *name)
+{
+  char **settings = g->backend_settings;
+  size_t namelen = strlen (name);
+  size_t i;
+
+  if (settings == NULL)
+    return NULL;
+
+  for (i = 0; settings[i] != NULL; ++i) {
+    if (STRCASEEQ (settings[i], name))
+      return ""; /* setting exists, no value */
+    if (STRCASEPREFIX (settings[i], name) && settings[i][namelen] == '=')
+      return &settings[i][namelen+1]; /* "name=...", return value */
+  }
+
+  return NULL;
+}
+
+/* If there a setting "name", "name=1", etc?  This is similar to
+ * fish/fish.c:is_true.
+ */
+int
+guestfs___get_backend_setting_bool (guestfs_h *g, const char *name)
+{
+  const char *value = guestfs___get_backend_setting (g, name);
+
+  if (value == NULL)
+    return 0;
+
+  if (STREQ (value, ""))
+    return 1;
+
+  if (STREQ (value, "1") ||
+      STRCASEEQ (value, "true") ||
+      STRCASEEQ (value, "t") ||
+      STRCASEEQ (value, "yes") ||
+      STRCASEEQ (value, "y") ||
+      STRCASEEQ (value, "on"))
+    return 1;
+
+  return 0;
+}

test-tool/test-tool.c

@@ -90,6 +90,7 @@ main (int argc, char *argv[])
   size_t i;
   struct guestfs_version *vers;
   char *p;
+  char **pp;
   guestfs_h *g;
   char *qemu = NULL;
   int qemu_use_wrapper;
@@ -230,6 +231,16 @@ main (int argc, char *argv[])
   p = guestfs_get_backend (g);
   printf ("guestfs_get_backend: %s\n", p ? : "(null)");
   free (p);
+  pp = guestfs_get_backend_settings (g);
+  printf ("guestfs_get_backend_settings: [");
+  for (i = 0; pp[i] != NULL; ++i) {
+    if (i > 0)
+      printf (", ");
+    printf ("%s", pp[i]);
+    free (pp[i]);
+  }
+  printf ("]\n");
+  free (pp);
   printf ("guestfs_get_autosync: %d\n", guestfs_get_autosync (g));
   p = guestfs_get_cachedir (g);
   printf ("guestfs_get_cachedir: %s\n", p ? : "(null)");