qemu-option: warn for short-form boolean options

Options such as "server" or "nowait", that are commonly found in -chardev,
are sugar for "server=on" and "wait=off".  This is quite surprising and
also does not have any notion of typing attached.  It is even possible to
do "-device e1000,noid" and get a device with "id=off".

Deprecate it and print a warning when it is encountered.  In general,
this short form for boolean options only seems to be in wide use for
-chardev and -spice.

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

docs/system/deprecated.rst

@@ -127,6 +127,12 @@ Drives with interface types other than ``if=none`` are for onboard
 devices.  It is possible to use drives the board doesn't pick up with
 -device.  This usage is now deprecated.  Use ``if=none`` instead.
 
+Short-form boolean options (since 6.0)
+''''''''''''''''''''''''''''''''''''''
+
+Boolean options such as ``share=on``/``share=off`` could be written
+in short form as ``share`` and ``noshare``.  This is now deprecated
+and will cause a warning.
 
 QEMU Machine Protocol (QMP) commands
 ------------------------------------

tests/test-qemu-opts.c

@@ -515,7 +515,7 @@ static void test_opts_parse(void)
     error_free_or_abort(&err);
     g_assert(!opts);
 
-    /* Implied value */
+    /* Implied value (qemu_opts_parse warns but accepts it) */
     opts = qemu_opts_parse(&opts_list_03, "an,noaus,noaus=",
                            false, &error_abort);
     g_assert_cmpuint(opts_count(opts), ==, 3);

util/qemu-option.c

@@ -756,10 +756,12 @@ void qemu_opts_print(QemuOpts *opts, const char *separator)
 
 static const char *get_opt_name_value(const char *params,
                                       const char *firstname,
+                                      bool warn_on_flag,
                                       bool *help_wanted,
                                       char **name, char **value)
 {
     const char *p;
+    const char *prefix = "";
     size_t len;
     bool is_help = false;
 
@@ -776,10 +778,15 @@ static const char *get_opt_name_value(const char *params,
             if (strncmp(*name, "no", 2) == 0) {
                 memmove(*name, *name + 2, strlen(*name + 2) + 1);
                 *value = g_strdup("off");
+                prefix = "no";
             } else {
                 *value = g_strdup("on");
                 is_help = is_help_option(*name);
             }
+            if (!is_help && warn_on_flag) {
+                warn_report("short-form boolean option '%s%s' deprecated", prefix, *name);
+                error_printf("Please use %s=%s instead\n", *name, *value);
+            }
         }
     } else {
         /* found "foo=bar,more" */
@@ -801,14 +808,14 @@ static const char *get_opt_name_value(const char *params,
 
 static bool opts_do_parse(QemuOpts *opts, const char *params,
                           const char *firstname, bool prepend,
-                          bool *help_wanted, Error **errp)
+                          bool warn_on_flag, bool *help_wanted, Error **errp)
 {
     char *option, *value;
     const char *p;
     QemuOpt *opt;
 
     for (p = params; *p;) {
-        p = get_opt_name_value(p, firstname, help_wanted, &option, &value);
+        p = get_opt_name_value(p, firstname, warn_on_flag, help_wanted, &option, &value);
         if (help_wanted && *help_wanted) {
             g_free(option);
             g_free(value);
@@ -839,7 +846,7 @@ static char *opts_parse_id(const char *params)
     char *name, *value;
 
     for (p = params; *p;) {
-        p = get_opt_name_value(p, NULL, NULL, &name, &value);
+        p = get_opt_name_value(p, NULL, false, NULL, &name, &value);
         if (!strcmp(name, "id")) {
             g_free(name);
             return value;
@@ -858,7 +865,7 @@ bool has_help_option(const char *params)
     bool ret = false;
 
     for (p = params; *p;) {
-        p = get_opt_name_value(p, NULL, &ret, &name, &value);
+        p = get_opt_name_value(p, NULL, false, &ret, &name, &value);
         g_free(name);
         g_free(value);
         if (ret) {
@@ -878,12 +885,12 @@ bool has_help_option(const char *params)
 bool qemu_opts_do_parse(QemuOpts *opts, const char *params,
                        const char *firstname, Error **errp)
 {
-    return opts_do_parse(opts, params, firstname, false, NULL, errp);
+    return opts_do_parse(opts, params, firstname, false, false, NULL, errp);
 }
 
 static QemuOpts *opts_parse(QemuOptsList *list, const char *params,
                             bool permit_abbrev, bool defaults,
-                            bool *help_wanted, Error **errp)
+                            bool warn_on_flag, bool *help_wanted, Error **errp)
 {
     const char *firstname;
     char *id = opts_parse_id(params);
@@ -906,8 +913,8 @@ static QemuOpts *opts_parse(QemuOptsList *list, const char *params,
         return NULL;
     }
 
-    if (!opts_do_parse(opts, params, firstname, defaults, help_wanted,
-                       errp)) {
+    if (!opts_do_parse(opts, params, firstname, defaults,
+                       warn_on_flag, help_wanted, errp)) {
         qemu_opts_del(opts);
         return NULL;
     }
@@ -925,7 +932,7 @@ static QemuOpts *opts_parse(QemuOptsList *list, const char *params,
 QemuOpts *qemu_opts_parse(QemuOptsList *list, const char *params,
                           bool permit_abbrev, Error **errp)
 {
-    return opts_parse(list, params, permit_abbrev, false, NULL, errp);
+    return opts_parse(list, params, permit_abbrev, false, false, NULL, errp);
 }
 
 /**
@@ -943,7 +950,7 @@ QemuOpts *qemu_opts_parse_noisily(QemuOptsList *list, const char *params,
     QemuOpts *opts;
     bool help_wanted = false;
 
-    opts = opts_parse(list, params, permit_abbrev, false,
+    opts = opts_parse(list, params, permit_abbrev, false, true,
                       opts_accepts_any(list) ? NULL : &help_wanted,
                       &err);
     if (!opts) {
@@ -962,7 +969,7 @@ void qemu_opts_set_defaults(QemuOptsList *list, const char *params,
 {
     QemuOpts *opts;
 
-    opts = opts_parse(list, params, permit_abbrev, true, NULL, NULL);
+    opts = opts_parse(list, params, permit_abbrev, true, false, NULL, NULL);
     assert(opts);
 }