config: do not save unknown sections

Unknown sections are sections whose name does not match any module in
the module bank. Until now, any unknown section in vlcrc was copied
verbatim when the preferences are saved. In principles, that would
preserve settings for modules that are not available in the current
copy of VLC.

There is a fatal flaw with that approach: When VLC is updated, some
modules may change name. Also some configuration items may be moved
from one module to another. As a consequence, configuration items may
end up in a different section than they previously were. Then vlcrc
will end up with multiple conflicting copies of the same configuration
item: first the current value for the preferences in the new
section, then the old value from the copied old section. When vlcrc is
loaded again, the old copy will override the new one since it is parsed
last. Essentially, the configuration item cannot be changed via
preferences until vlcrc is manually edited or preferences are reset.

I would rather loose settings for old plugins.

src/config/file.c

@@ -348,7 +348,6 @@ static int config_PrepareDir (vlc_object_t *obj)
  */
 int config_SaveConfigFile (vlc_object_t *p_this)
 {
-    char *permanent = NULL, *temporary = NULL;
 
     if( config_PrepareDir( p_this ) )
     {
@@ -356,89 +355,30 @@ int config_SaveConfigFile (vlc_object_t *p_this)
         return -1;
     }
 
-    /* List all available modules */
-    module_t **list = module_list_get (NULL);
-
-    char *bigbuf = NULL;
-    size_t bigsize = 0;
-    FILE *file = config_OpenConfigFile (p_this);
-    if (file != NULL)
+    /*
+     * Save module config in file
+     */
+    char *temporary;
+    char *permanent = config_GetConfigFile (p_this);
+    if (permanent == NULL)
+        return -1;
+    if (asprintf (&temporary, "%s.%u", permanent, getpid ()) == -1)
+    {
+        free (permanent);
+        return -1;
+    }
+    else
     {
         struct stat st;
 
         /* Some users make vlcrc read-only to prevent changes.
          * The atomic replacement scheme breaks this "feature",
          * so we check for read-only by hand. */
-        if (fstat (fileno (file), &st)
-         || !(st.st_mode & S_IWUSR))
+        if (stat (permanent, &st) == 0 && !(st.st_mode & S_IWUSR))
         {
             msg_Err (p_this, "configuration file is read-only");
             goto error;
         }
-
-        bigsize = (st.st_size < LONG_MAX) ? st.st_size : 0;
-        bigbuf = malloc (bigsize + 1);
-        if (bigbuf == NULL)
-            goto error;
-
-        /* backup file into memory, we only need to backup the sections we
-         * won't save later on */
-        char *p_index = bigbuf;
-        char *line = NULL;
-        size_t bufsize;
-        ssize_t linelen;
-        bool backup = false;
-
-        while ((linelen = getline (&line, &bufsize, file)) != -1)
-        {
-            if ((line[0] == '[') && (strchr (line,']') != NULL))
-            {
-                module_t *module;
-
-                /* we found a new section, check if we need to do a backup */
-                backup = true;
-                for (int i = 0; (module = list[i]) != NULL; i++)
-                {
-                    const char *objname = module_get_object (module);
-
-                    if (!strncmp (line + 1, objname, strlen (objname)))
-                    {
-                        backup = false; /* no, we will rewrite it! */
-                        break;
-                    }
-                }
-            }
-
-            /* save line if requested and line is valid (doesn't begin with a
-             * space, tab, or eol) */
-            if (backup && !memchr ("\n\t ", line[0], 3))
-            {
-                memcpy (p_index, line, linelen);
-                p_index += linelen;
-            }
-        }
-        fclose (file);
-        file = NULL;
-        free (line);
-        *p_index = '\0';
-        bigsize = p_index - bigbuf;
-    }
-
-    /*
-     * Save module config in file
-     */
-    permanent = config_GetConfigFile (p_this);
-    if (!permanent)
-    {
-        module_list_free (list);
-        goto error;
-    }
-
-    if (asprintf (&temporary, "%s.%u", permanent, getpid ()) == -1)
-    {
-        temporary = NULL;
-        module_list_free (list);
-        goto error;
     }
 
     /* Configuration lock must be taken before vlcrc serializer below. */
@@ -454,17 +394,15 @@ int config_SaveConfigFile (vlc_object_t *p_this)
     {
         vlc_rwlock_unlock (&config_lock);
         vlc_mutex_unlock (&lock);
-        module_list_free (list);
         goto error;
     }
-    file = fdopen (fd, "wt");
+    FILE *file = fdopen (fd, "wt");
     if (file == NULL)
     {
         msg_Err (p_this, "cannot create configuration file: %m");
         vlc_rwlock_unlock (&config_lock);
         close (fd);
         vlc_mutex_unlock (&lock);
-        module_list_free (list);
         goto error;
     }
 
@@ -487,6 +425,7 @@ int config_SaveConfigFile (vlc_object_t *p_this)
     vlc_rwlock_rdlock (&config_lock);*/
 
     /* Look for the selected module, if NULL then save everything */
+    module_t **list = module_list_get (NULL);
     module_t *p_parser;
     for (int i = 0; (p_parser = list[i]) != NULL; i++)
     {
@@ -551,12 +490,6 @@ int config_SaveConfigFile (vlc_object_t *p_this)
         freelocale (loc);
     }
 
-    /*
-     * Restore old settings from the config in file
-     */
-    if (bigsize)
-        fwrite (bigbuf, 1, bigsize, file);
-
     /*
      * Flush to disk and replace atomically
      */
@@ -566,7 +499,7 @@ int config_SaveConfigFile (vlc_object_t *p_this)
         vlc_unlink (temporary);
         vlc_mutex_unlock (&lock);
         msg_Err (p_this, "cannot write configuration file");
-        clearerr (file);
+        fclose (file);
         goto error;
     }
 #if defined(__APPLE__) || defined(__ANDROID__)
@@ -591,15 +524,11 @@ int config_SaveConfigFile (vlc_object_t *p_this)
 
     free (temporary);
     free (permanent);
-    free (bigbuf);
     return 0;
 
 error:
-    if( file )
-        fclose( file );
     free (temporary);
     free (permanent);
-    free (bigbuf);
     return -1;
 }