QemuOpts: command line switches for the config file.

Adds -readconfig and -writeconfig command line switches to read/write
QemuOpts from config file.

In theory you should be able to do:

  qemu < machine config cmd line switches here > -writeconfig vm.cfg
  qemu -readconfig vm.cfg

In practice it will not work.  Not all command line switches are
converted to QemuOpts, so you'll have to keep the not-yet converted ones
on the second line.  Also there might be bugs lurking which prevent even
the converted ones from working correctly.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

qemu-options.hx

@@ -1915,3 +1915,8 @@ DEF("semihosting", 0, QEMU_OPTION_semihosting,
 DEF("old-param", 0, QEMU_OPTION_old_param,
     "-old-param      old param mode\n")
 #endif
+DEF("readconfig", HAS_ARG, QEMU_OPTION_readconfig,
+    "-readconfig <file>\n")
+DEF("writeconfig", HAS_ARG, QEMU_OPTION_writeconfig,
+    "-writeconfig <file>\n"
+    "                read/write config file")

vl.c

@@ -5364,6 +5364,36 @@ int main(int argc, char **argv, char **envp)
                 xen_mode = XEN_ATTACH;
                 break;
 #endif
+            case QEMU_OPTION_readconfig:
+                {
+                    FILE *fp;
+                    fp = fopen(optarg, "r");
+                    if (fp == NULL) {
+                        fprintf(stderr, "open %s: %s\n", optarg, strerror(errno));
+                        exit(1);
+                    }
+                    if (qemu_config_parse(fp) != 0) {
+                        exit(1);
+                    }
+                    fclose(fp);
+                    break;
+                }
+            case QEMU_OPTION_writeconfig:
+                {
+                    FILE *fp;
+                    if (strcmp(optarg, "-") == 0) {
+                        fp = stdout;
+                    } else {
+                        fp = fopen(optarg, "w");
+                        if (fp == NULL) {
+                            fprintf(stderr, "open %s: %s\n", optarg, strerror(errno));
+                            exit(1);
+                        }
+                    }
+                    qemu_config_write(fp);
+                    fclose(fp);
+                    break;
+                }
             }
         }
     }