vl: deprecate -writeconfig

The functionality of -writeconfig is limited and the code
does not even try to detect cases where it prints incorrect
syntax (for example if values have a quote in them, since
qemu_config_parse does not support any kind of escaping)
so remove it.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

docs/system/deprecated.rst

@@ -146,6 +146,13 @@ library enabled as a cryptography provider.
 Neither the ``nettle`` library, or the built-in cryptography provider are
 supported on FIPS enabled hosts.
 
+``-writeconfig`` (since 6.0)
+'''''''''''''''''''''''''''''
+
+The ``-writeconfig`` option is not able to serialize the entire contents
+of the QEMU command line.  It is thus considered a failed experiment
+and deprecated, with no current replacement.
+
 QEMU Machine Protocol (QMP) commands
 ------------------------------------
 

qemu-options.hx

@@ -4335,13 +4335,8 @@ SRST
 ERST
 DEF("writeconfig", HAS_ARG, QEMU_OPTION_writeconfig,
     "-writeconfig <file>\n"
-    "                read/write config file\n", QEMU_ARCH_ALL)
+    "                read/write config file (deprecated)\n", QEMU_ARCH_ALL)
 SRST
-``-writeconfig file``
-    Write device configuration to file. The file can be either filename
-    to save command line and device configuration into file or dash
-    ``-``) character to print the output to stdout. This can be later
-    used as input file for ``-readconfig`` option.
 ERST
 
 DEF("no-user-config", 0, QEMU_OPTION_nouserconfig,

softmmu/vl.c

@@ -3356,6 +3356,7 @@ void qemu_init(int argc, char **argv, char **envp)
             case QEMU_OPTION_writeconfig:
                 {
                     FILE *fp;
+                    warn_report("-writeconfig is deprecated and will go away without a replacement");
                     if (strcmp(optarg, "-") == 0) {
                         fp = stdout;
                     } else {