error: Simplify error sink setup

qemu_error_sink can either point to a monitor or a file.  In practice,
it always points to the current monitor if we have one, else to
stderr.  Simply route errors to the current monitor or else to stderr,
and remove qemu_error_sink along with the functions to control it.

Actually, the old code switches the sink slightly later, in
handle_user_command() and handle_qmp_command(), than it gets switched
now, implicitly, by setting the current monitor in monitor_read() and
monitor_control_read().  Likewise, it switches back slightly earlier
(same places).  Doesn't make a difference, because there are no calls
of qemu_error() in between.

monitor.c

@@ -3971,8 +3971,6 @@ static void handle_user_command(Monitor *mon, const char *cmdline)
     if (!cmd)
         goto out;
 
-    qemu_errors_to_mon(mon);
-
     if (monitor_handler_is_async(cmd)) {
         user_async_cmd_handler(mon, cmd, qdict);
     } else if (monitor_handler_ported(cmd)) {
@@ -3984,8 +3982,6 @@ static void handle_user_command(Monitor *mon, const char *cmdline)
     if (monitor_has_error(mon))
         monitor_print_error(mon);
 
-    qemu_errors_to_previous();
-
 out:
     QDECREF(qdict);
 }
@@ -4387,7 +4383,6 @@ static void handle_qmp_command(JSONMessageParser *parser, QList *tokens)
     const char *cmd_name, *info_item;
 
     args = NULL;
-    qemu_errors_to_mon(mon);
 
     obj = json_parser_parse(tokens, NULL);
     if (!obj) {
@@ -4468,7 +4463,6 @@ err_out:
     monitor_protocol_emitter(mon, NULL);
 out:
     QDECREF(args);
-    qemu_errors_to_previous();
 }
 
 /**

qemu-error.c

@@ -2,70 +2,17 @@
 #include "monitor.h"
 #include "sysemu.h"
 
-typedef struct QemuErrorSink QemuErrorSink;
-struct QemuErrorSink {
-    enum {
-        ERR_SINK_FILE,
-        ERR_SINK_MONITOR,
-    } dest;
-    union {
-        FILE    *fp;
-        Monitor *mon;
-    };
-    QemuErrorSink *previous;
-};
-
-static QemuErrorSink *qemu_error_sink;
-
-void qemu_errors_to_file(FILE *fp)
-{
-    QemuErrorSink *sink;
-
-    sink = qemu_mallocz(sizeof(*sink));
-    sink->dest = ERR_SINK_FILE;
-    sink->fp = fp;
-    sink->previous = qemu_error_sink;
-    qemu_error_sink = sink;
-}
-
-void qemu_errors_to_mon(Monitor *mon)
-{
-    QemuErrorSink *sink;
-
-    sink = qemu_mallocz(sizeof(*sink));
-    sink->dest = ERR_SINK_MONITOR;
-    sink->mon = mon;
-    sink->previous = qemu_error_sink;
-    qemu_error_sink = sink;
-}
-
-void qemu_errors_to_previous(void)
-{
-    QemuErrorSink *sink;
-
-    assert(qemu_error_sink != NULL);
-    sink = qemu_error_sink;
-    qemu_error_sink = sink->previous;
-    qemu_free(sink);
-}
-
 void qemu_error(const char *fmt, ...)
 {
     va_list args;
 
-    assert(qemu_error_sink != NULL);
-    switch (qemu_error_sink->dest) {
-    case ERR_SINK_FILE:
-        va_start(args, fmt);
-        vfprintf(qemu_error_sink->fp, fmt, args);
-        va_end(args);
-        break;
-    case ERR_SINK_MONITOR:
-        va_start(args, fmt);
-        monitor_vprintf(qemu_error_sink->mon, fmt, args);
-        va_end(args);
-        break;
+    va_start(args, fmt);
+    if (cur_mon) {
+        monitor_vprintf(cur_mon, fmt, args);
+    } else {
+        vfprintf(stderr, fmt, args);
     }
+    va_end(args);
 }
 
 void qemu_error_internal(const char *file, int linenr, const char *func,
@@ -74,19 +21,14 @@ void qemu_error_internal(const char *file, int linenr, const char *func,
     va_list va;
     QError *qerror;
 
-    assert(qemu_error_sink != NULL);
-
     va_start(va, fmt);
     qerror = qerror_from_info(file, linenr, func, fmt, &va);
     va_end(va);
 
-    switch (qemu_error_sink->dest) {
-    case ERR_SINK_FILE:
+    if (cur_mon) {
+        monitor_set_error(cur_mon, qerror);
+    } else {
         qerror_print(qerror);
         QDECREF(qerror);
-        break;
-    case ERR_SINK_MONITOR:
-        monitor_set_error(qemu_error_sink->mon, qerror);
-        break;
     }
 }

sysemu.h

@@ -73,9 +73,6 @@ int qemu_savevm_state_complete(Monitor *mon, QEMUFile *f);
 void qemu_savevm_state_cancel(Monitor *mon, QEMUFile *f);
 int qemu_loadvm_state(QEMUFile *f);
 
-void qemu_errors_to_file(FILE *fp);
-void qemu_errors_to_mon(Monitor *mon);
-void qemu_errors_to_previous(void);
 void qemu_error(const char *fmt, ...) __attribute__ ((format(printf, 1, 2)));
 void qemu_error_internal(const char *file, int linenr, const char *func,
                          const char *fmt, ...)

vl.c

@@ -4864,7 +4864,6 @@ int main(int argc, char **argv, char **envp)
 
     init_clocks();
 
-    qemu_errors_to_file(stderr);
     qemu_cache_utils_init(envp);
 
     QLIST_INIT (&vm_change_state_head);