hmp: human-monitor-command: stop using the Memory chardev driver

The Memory chardev driver was added because, as the Monitor's output
buffer was static, we needed a way to accumulate the output of an
HMP commmand when ran by human-monitor-command.

However, the Monitor's output buffer is now dynamic, so it's possible
for the human-monitor-command to use it instead of the Memory chardev
driver.

This commit does that change, but there are two important
observations about it:

 1. We need a way to signal to the Monitor that it shouldn't call
    chardev functions when flushing its output. This is done
    by adding a new flag to the Monitor object called skip_flush
	(which is set to true by qmp_human_monitor_command())

 2. The current code has buffered semantics: QMP clients will
    only see a command's output if it flushes its output with
	a new-line character. This commit changes this to unbuffered,
	which means that QMP clients will see a command's output
	whenever the command prints anything.

	I don't think this will matter in practice though, as I believe
	all HMP commands print the new-line character anyway.
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Acked-by: NGerd Hoffmann <kraxel@redhat.com>

monitor.c

@@ -188,6 +188,7 @@ struct Monitor {
     int reset_seen;
     int flags;
     int suspend_cnt;
+    bool skip_flush;
     QString *outbuf;
     ReadLineState *rs;
     MonitorControl *mc;
@@ -273,6 +274,10 @@ void monitor_flush(Monitor *mon)
     size_t len;
     const char *buf;
 
+    if (mon->skip_flush) {
+        return;
+    }
+
     buf = qstring_get_str(mon->outbuf);
     len = qstring_get_length(mon->outbuf);
 
@@ -675,13 +680,10 @@ char *qmp_human_monitor_command(const char *command_line, bool has_cpu_index,
 {
     char *output = NULL;
     Monitor *old_mon, hmp;
-    CharDriverState mchar;
 
     memset(&hmp, 0, sizeof(hmp));
     hmp.outbuf = qstring_new();
-
-    qemu_chr_init_mem(&mchar);
-    hmp.chr = &mchar;
+    hmp.skip_flush = true;
 
     old_mon = cur_mon;
     cur_mon = &hmp;
@@ -699,17 +701,14 @@ char *qmp_human_monitor_command(const char *command_line, bool has_cpu_index,
     handle_user_command(&hmp, command_line);
     cur_mon = old_mon;
 
-    if (qemu_chr_mem_osize(hmp.chr) > 0) {
-        QString *str = qemu_chr_mem_to_qs(hmp.chr);
-        output = g_strdup(qstring_get_str(str));
-        QDECREF(str);
+    if (qstring_get_length(hmp.outbuf) > 0) {
+        output = g_strdup(qstring_get_str(hmp.outbuf));
     } else {
         output = g_strdup("");
     }
 
 out:
     QDECREF(hmp.outbuf);
-    qemu_chr_close_mem(hmp.chr);
     return output;
 }