implement -no-user-config command-line option (v3)

Changes v2 -> v3:
 - Rebase against latest qemu.git

Changes v1 -> v2:
 - Change 'userconfig' field/variables to bool instead of int
 - Coding style change

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

arch_init.c

@@ -114,19 +114,24 @@ const uint32_t arch_type = QEMU_ARCH;
 
 static struct defconfig_file {
     const char *filename;
+    /* Indicates it is an user config file (disabled by -no-user-config) */
+    bool userconfig;
 } default_config_files[] = {
-    { CONFIG_QEMU_CONFDIR "/qemu.conf" },
-    { CONFIG_QEMU_CONFDIR "/target-" TARGET_ARCH ".conf" },
+    { CONFIG_QEMU_CONFDIR "/qemu.conf",                   true },
+    { CONFIG_QEMU_CONFDIR "/target-" TARGET_ARCH ".conf", true },
     { NULL }, /* end of list */
 };
 
 
-int qemu_read_default_config_files(void)
+int qemu_read_default_config_files(bool userconfig)
 {
     int ret;
     struct defconfig_file *f;
 
     for (f = default_config_files; f->filename; f++) {
+        if (!userconfig && f->userconfig) {
+            continue;
+        }
         ret = qemu_read_config_file(f->filename);
         if (ret < 0 && ret != -ENOENT) {
             return ret;

qemu-config.h

@@ -18,6 +18,6 @@ int qemu_read_config_file(const char *filename);
 
 /* Read default Qemu config files
  */
-int qemu_read_default_config_files(void);
+int qemu_read_default_config_files(bool userconfig);
 
 #endif /* QEMU_CONFIG_H */

qemu-options.hx

@@ -2685,9 +2685,19 @@ DEF("nodefconfig", 0, QEMU_OPTION_nodefconfig,
 STEXI
 @item -nodefconfig
 @findex -nodefconfig
-Normally QEMU loads a configuration file from @var{sysconfdir}/qemu.conf and
-@var{sysconfdir}/target-@var{ARCH}.conf on startup.  The @code{-nodefconfig}
-option will prevent QEMU from loading these configuration files at startup.
+Normally QEMU loads configuration files from @var{sysconfdir} and @var{datadir} at startup.
+The @code{-nodefconfig} option will prevent QEMU from loading any of those config files.
+ETEXI
+DEF("no-user-config", 0, QEMU_OPTION_nouserconfig,
+    "-no-user-config\n"
+    "                do not load user-provided config files at startup\n",
+    QEMU_ARCH_ALL)
+STEXI
+@item -no-user-config
+@findex -no-user-config
+The @code{-no-user-config} option makes QEMU not load any of the user-provided
+config files on @var{sysconfdir}, but won't make it skip the QEMU-provided config
+files from @var{datadir}.
 ETEXI
 DEF("trace", HAS_ARG, QEMU_OPTION_trace,
     "-trace [events=<file>][,file=<file>]\n"

vl.c

@@ -2284,6 +2284,7 @@ int main(int argc, char **argv, char **envp)
     int show_vnc_port = 0;
 #endif
     bool defconfig = true;
+    bool userconfig = true;
     const char *log_mask = NULL;
     const char *log_file = NULL;
     GMemVTable mem_trace = {
@@ -2352,13 +2353,16 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_nodefconfig:
                 defconfig = false;
                 break;
+            case QEMU_OPTION_nouserconfig:
+                userconfig = false;
+                break;
             }
         }
     }
 
     if (defconfig) {
         int ret;
-        ret = qemu_read_default_config_files();
+        ret = qemu_read_default_config_files(userconfig);
         if (ret < 0) {
             exit(1);
         }