monitor: restrict command getfd to POSIX hosts

Currently, the function will simply fail if ancillary fds are not
provided, for ex on unsupported platforms.

This changes the failure from:

    {"error": {"class": "GenericError", "desc": "No file descriptor
    supplied via SCM_RIGHTS"}}

to:

    {"error": {"class": "CommandNotFound", "desc": "The command getfd
    has not been found"}}

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>

hmp-commands.hx

@@ -1486,6 +1486,7 @@ SRST
   Inject an MCE on the given CPU (x86 only).
 ERST
 
+#ifdef CONFIG_POSIX
     {
         .name       = "getfd",
         .args_type  = "fdname:s",
@@ -1501,6 +1502,7 @@ SRST
   mechanism on unix sockets, it is stored using the name *fdname* for
   later use by other monitor commands.
 ERST
+#endif
 
     {
         .name       = "closefd",

monitor/fds.c

@@ -98,6 +98,7 @@ static bool monitor_add_fd(Monitor *mon, int fd, const char *fdname, Error **err
     return true;
 }
 
+#ifdef CONFIG_POSIX
 void qmp_getfd(const char *fdname, Error **errp)
 {
     Monitor *cur_mon = monitor_cur();
@@ -111,6 +112,7 @@ void qmp_getfd(const char *fdname, Error **errp)
 
     monitor_add_fd(cur_mon, fd, fdname, errp);
 }
+#endif
 
 void qmp_closefd(const char *fdname, Error **errp)
 {

monitor/hmp-cmds.c

@@ -192,6 +192,7 @@ void hmp_change(Monitor *mon, const QDict *qdict)
     hmp_handle_error(mon, err);
 }
 
+#ifdef CONFIG_POSIX
 void hmp_getfd(Monitor *mon, const QDict *qdict)
 {
     const char *fdname = qdict_get_str(qdict, "fdname");
@@ -200,6 +201,7 @@ void hmp_getfd(Monitor *mon, const QDict *qdict)
     qmp_getfd(fdname, &err);
     hmp_handle_error(mon, err);
 }
+#endif
 
 void hmp_closefd(Monitor *mon, const QDict *qdict)
 {

qapi/misc.json

@@ -273,7 +273,7 @@
 # <- { "return": {} }
 #
 ##
-{ 'command': 'getfd', 'data': {'fdname': 'str'} }
+{ 'command': 'getfd', 'data': {'fdname': 'str'}, 'if': 'CONFIG_POSIX' }
 
 ##
 # @get-win32-socket: