[Qemu-devel] [PATCH 19/19] Add a -capabilities argument to allow easy query for static QEMU info

["Daniel P. Berrange" <berrange@redhat.com>]

The QMP monitor provides a number of commands for querying info about
the QEMU binary capabilities. Given that these commands don't take
any options and just return static data, requiring the use of QMP is
unnecessarily onerous. This adds a new '-capabilities' command line
argument as a syntactic sugar for accessing the QMP commands that
just return static QEMU binary capabilities.

Setting the '-capabilities' argument causes QEMU to output the requested
data on stdout, pretty printed in JSON format. The argument expects an
associated value to identify the data to be printed. This can be one of
the strings version|machines|devices|cputypes|target|commands|argv|netdev

To query all possible data at once, the shorthand 'all' is allowed.

The output is a QDict where the key is the type of data requested, and
the value is the JSON data from the associated monitor command. For
example:

  $ qemu -capabilities all
  {
    "machines": [
        {
            "name": "pc-0.13",
            "description": "Standard PC",
            "default": 0
        },
        {
            "name": "pc",
            ....
        }
        ....
     }
     "version": {
        "qemu": {
            "micro": 50,
            "minor": 12,
            "major": 0
        },
        "package": ""
     },
     "target": {
        "arch": "i386",
        "wordsize": 32,
     ...
   }

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 monitor.c       |    4 +-
 monitor.h       |    2 +
 qemu-options.hx |    9 +++++
 vl.c            |  100 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 113 insertions(+), 2 deletions(-)

diff --git a/monitor.c b/monitor.c
index 6203f75..401a27a 100644
--- a/monitor.c
+++ b/monitor.c
@@ -711,7 +711,7 @@ static void do_info_version_print(Monitor *mon, const QObject *data)
  *
  * { qemu: { "major": 0, "minor": 11, "micro": 5 }, "package": "" }
  */
-static void do_info_version(Monitor *mon, QObject **ret_data)
+void do_info_version(Monitor *mon, QObject **ret_data)
 {
     const char *version = QEMU_VERSION;
     int major = 0, minor = 0, micro = 0;
@@ -760,7 +760,7 @@ static QObject *get_cmd_dict(const char *name)
     return qobject_from_jsonf("{ 'name': %s }", p);
 }
 
-static void do_info_commands(Monitor *mon, QObject **ret_data)
+void do_info_commands(Monitor *mon, QObject **ret_data)
 {
     QList *cmd_list;
     const mon_cmd_t *cmd;
diff --git a/monitor.h b/monitor.h
index 733485f..dc376af 100644
--- a/monitor.h
+++ b/monitor.h
@@ -57,5 +57,7 @@ typedef void (MonitorCompletion)(void *opaque, QObject *ret_data);
 void monitor_set_error(Monitor *mon, QError *qerror);
 
 void do_info_argv(Monitor *mon, QObject **data);
+void do_info_version(Monitor *mon, QObject **ret_data);
+void do_info_commands(Monitor *mon, QObject **ret_data);
 
 #endif /* !MONITOR_H */
diff --git a/qemu-options.hx b/qemu-options.hx
index a6928b7..5f82347 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -27,6 +27,15 @@ STEXI
 Display version information and exit
 ETEXI
 
+DEF("capabilities", HAS_ARG, QEMU_OPTION_capabilities,
+    "-capabilities   all|version|machines|devices|cputypes|target|commands|argv|netdev\n"
+    "                display capabilities of the QEMU binary and exit\n", QEMU_ARCH_ALL)
+STEXI
+@item -capabilities  all|version|machines|devices|cputypes|target|commands|argv|netdev
+@findex -capabilities
+Display capabilities of the QEMU binary and exit
+ETEXI
+
 DEF("M", HAS_ARG, QEMU_OPTION_M,
     "-M machine      select emulated machine (-M ? for list)\n", QEMU_ARCH_ALL)
 STEXI
diff --git a/vl.c b/vl.c
index de010cc..1f165a1 100644
--- a/vl.c
+++ b/vl.c
@@ -1988,6 +1988,97 @@ static void version(void)
 }
 
 
+enum {
+    QEMU_CAPS_VERSION,
+    QEMU_CAPS_MACHINES,
+    QEMU_CAPS_DEVICES,
+    QEMU_CAPS_CPUTYPES,
+    QEMU_CAPS_TARGET,
+    QEMU_CAPS_COMMANDS,
+    QEMU_CAPS_ARGV,
+    QEMU_CAPS_NETDEV,
+    QEMU_CAPS_CONFIG,
+
+    QEMU_CAPS_LAST
+};
+
+QEMU_ENUM_DECL(qemu_caps_flag);
+QEMU_ENUM_IMPL(qemu_caps_flag, QEMU_CAPS_LAST,
+               "version",
+               "machines",
+               "devices",
+               "cputypes",
+               "target",
+               "commands",
+               "argv",
+               "netdev",
+               "config");
+
+static int qemu_caps_flags_from_string(const char *flagsstr)
+{
+    if (strcmp(flagsstr, "all") == 0)
+        return ~0;
+    else {
+        int i = qemu_caps_flag_from_string(flagsstr);
+        if (i < 0)
+            return 0;
+        return (1 << i);
+    }
+
+    return 0;
+}
+typedef void (*qemu_caps_handler)(Monitor *mon, QObject **);
+
+/* Binding capabilities to a subset of monitor commands.
+ * The commands must only use static binary state, no
+ * VM runtime state and must accept mon=NULL
+ */
+static const qemu_caps_handler qemu_caps_handlers[] = {
+    do_info_version,
+    do_info_machines,
+    do_info_devices,
+    do_info_cpu_types,
+    do_info_target,
+    do_info_commands,
+    do_info_argv,
+    do_info_netdev,
+    do_info_config,
+};
+verify(ARRAY_SIZE(qemu_caps_handlers) == QEMU_CAPS_LAST);
+
+static void qemu_show_caps(const char *flagsstr)
+{
+    QDict *data = qdict_new();
+    QString *json;
+    int i;
+    int flags;
+
+    flags = qemu_caps_flags_from_string(flagsstr);
+    if (flags == 0) {
+        fprintf(stderr, "Unknown capabilities '%s'\n", flagsstr);
+        exit(1);
+    }
+
+    for (i = 0 ; i < QEMU_CAPS_LAST ; i++) {
+        if (flags & (1 << i)) {
+            QObject *val;
+            qemu_caps_handler handler = qemu_caps_handlers[i];
+            const char *name = qemu_caps_flag_to_string(i);
+            (*handler)(NULL, &val);
+            qdict_put_obj(data, name, val);
+        }
+    }
+    json = qobject_to_json_pretty(QOBJECT(data));
+    assert(json != NULL);
+
+    qstring_append_chr(json, '\n');
+    fprintf(stdout, qstring_get_str(json));
+
+    QDECREF(json);
+
+}
+
+
 /**
  * do_info_argv():
  *
@@ -2647,6 +2738,7 @@ int main(int argc, char **argv, char **envp)
 #endif
     int show_vnc_port = 0;
     int defconfig = 1;
+    const char *showcaps = NULL;
 
     error_set_progname(argv[0]);
 
@@ -3020,6 +3112,9 @@ int main(int argc, char **argv, char **envp)
                 version();
                 exit(0);
                 break;
+            case QEMU_OPTION_capabilities:
+                showcaps = optarg;
+                break;
             case QEMU_OPTION_m: {
                 uint64_t value;
                 char *ptr;
@@ -3785,6 +3880,11 @@ int main(int argc, char **argv, char **envp)
     if (qemu_opts_foreach(&qemu_device_opts, device_help_func, NULL, 0) != 0)
         exit(0);
 
+    if (showcaps) {
+        qemu_show_caps(showcaps);
+        exit(0);
+    }
+
     if (watchdog) {
         i = select_watchdog(watchdog);
         if (i > 0)
-- 
1.6.6.1