monitor error: Make printf()-like functions return a value

printf() & friends return the number of characters written on success,
negative value on error.

monitor_printf(), monitor_vfprintf(), monitor_vprintf(),
error_printf(), error_printf_unless_qmp(), error_vprintf(), and
error_vprintf_unless_qmp() return void.  Some of them carry a TODO
comment asking for int instead.

Improve them to return int like printf() does.

This makes our use of monitor_printf() as fprintf_function slightly
less dirty: the function cast no longer adds a return value that isn't
there.  It still changes a parameter's pointer type.  That will be
addressed in a future commit.

monitor_vfprintf() always returns zero.  Improve it to return the
proper value.

Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20190417190641.26814-11-armbru@redhat.com>

include/monitor/monitor.h

@@ -28,9 +28,9 @@ void monitor_resume(Monitor *mon);
 int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp);
 int monitor_fd_param(Monitor *mon, const char *fdname, Error **errp);
 
-void monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
+int monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
     GCC_FMT_ATTR(2, 0);
-void monitor_printf(Monitor *mon, const char *fmt, ...) GCC_FMT_ATTR(2, 3);
+int monitor_printf(Monitor *mon, const char *fmt, ...) GCC_FMT_ATTR(2, 3);
 int monitor_fprintf(FILE *stream, const char *fmt, ...) GCC_FMT_ATTR(2, 3);
 void monitor_flush(Monitor *mon);
 int monitor_set_cpu(int cpu_index);
@@ -48,7 +48,7 @@ int monitor_fdset_dup_fd_add(int64_t fdset_id, int dup_fd);
 void monitor_fdset_dup_fd_remove(int dup_fd);
 int monitor_fdset_dup_fd_find(int dup_fd);
 
-void monitor_vfprintf(FILE *stream,
+int monitor_vfprintf(FILE *stream,
-                      const char *fmt, va_list ap) GCC_FMT_ATTR(2, 0);
+                     const char *fmt, va_list ap) GCC_FMT_ATTR(2, 0);
 
 #endif /* MONITOR_H */

include/qemu/error-report.h

@@ -30,10 +30,10 @@ void loc_set_none(void);
 void loc_set_cmdline(char **argv, int idx, int cnt);
 void loc_set_file(const char *fname, int lno);
 
-void error_vprintf(const char *fmt, va_list ap) GCC_FMT_ATTR(1, 0);
+int error_vprintf(const char *fmt, va_list ap) GCC_FMT_ATTR(1, 0);
-void error_printf(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
+int error_printf(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
-void error_vprintf_unless_qmp(const char *fmt, va_list ap) GCC_FMT_ATTR(1, 0);
+int error_vprintf_unless_qmp(const char *fmt, va_list ap) GCC_FMT_ATTR(1, 0);
-void error_printf_unless_qmp(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
+int error_printf_unless_qmp(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 
 void error_vreport(const char *fmt, va_list ap) GCC_FMT_ATTR(1, 0);
 void warn_vreport(const char *fmt, va_list ap) GCC_FMT_ATTR(1, 0);

monitor.c

@@ -430,15 +430,14 @@ void monitor_flush(Monitor *mon)
 }
 
 /* flush at every end of line */
-static void monitor_puts(Monitor *mon, const char *str)
+static int monitor_puts(Monitor *mon, const char *str)
 {
+    int i;
     char c;
 
     qemu_mutex_lock(&mon->mon_lock);
-    for(;;) {
+    for (i = 0; str[i]; i++) {
-        c = *str++;
+        c = str[i];
-        if (c == '\0')
-            break;
         if (c == '\n') {
             qstring_append_chr(mon->outbuf, '\r');
         }
@@ -448,39 +447,48 @@ static void monitor_puts(Monitor *mon, const char *str)
         }
     }
     qemu_mutex_unlock(&mon->mon_lock);
+
+    return i;
 }
 
-void monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
+int monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
 {
     char *buf;
+    int n;
 
     if (!mon)
-        return;
+        return -1;
 
     if (monitor_is_qmp(mon)) {
-        return;
+        return -1;
     }
 
     buf = g_strdup_vprintf(fmt, ap);
-    monitor_puts(mon, buf);
+    n = monitor_puts(mon, buf);
     g_free(buf);
+    return n;
 }
 
-void monitor_printf(Monitor *mon, const char *fmt, ...)
+int monitor_printf(Monitor *mon, const char *fmt, ...)
 {
+    int ret;
+
     va_list ap;
     va_start(ap, fmt);
-    monitor_vprintf(mon, fmt, ap);
+    ret = monitor_vprintf(mon, fmt, ap);
     va_end(ap);
+    return ret;
 }
 
 int monitor_fprintf(FILE *stream, const char *fmt, ...)
 {
+    int ret;
+
     va_list ap;
     va_start(ap, fmt);
-    monitor_vprintf((Monitor *)stream, fmt, ap);
+    ret = monitor_vprintf((Monitor *)stream, fmt, ap);
     va_end(ap);
-    return 0;
+    return ret;
 }
 
 static void qmp_send_response(Monitor *mon, const QDict *rsp)
@@ -4535,35 +4543,32 @@ static void monitor_readline_flush(void *opaque)
 
 /*
  * Print to current monitor if we have one, else to stream.
- * TODO should return int, so callers can calculate width, but that
- * requires surgery to monitor_vprintf().  Left for another day.
  */
-void monitor_vfprintf(FILE *stream, const char *fmt, va_list ap)
+int monitor_vfprintf(FILE *stream, const char *fmt, va_list ap)
 {
     if (cur_mon && !monitor_cur_is_qmp()) {
-        monitor_vprintf(cur_mon, fmt, ap);
+        return monitor_vprintf(cur_mon, fmt, ap);
-    } else {
-        vfprintf(stream, fmt, ap);
     }
+    return vfprintf(stream, fmt, ap);
 }
 
 /*
  * Print to current monitor if we have one, else to stderr.
- * TODO should return int, so callers can calculate width, but that
- * requires surgery to monitor_vprintf().  Left for another day.
  */
-void error_vprintf(const char *fmt, va_list ap)
+int error_vprintf(const char *fmt, va_list ap)
 {
-    monitor_vfprintf(stderr, fmt, ap);
+    return monitor_vfprintf(stderr, fmt, ap);
 }
 
-void error_vprintf_unless_qmp(const char *fmt, va_list ap)
+int error_vprintf_unless_qmp(const char *fmt, va_list ap)
 {
-    if (cur_mon && !monitor_cur_is_qmp()) {
+    if (!cur_mon) {
-        monitor_vprintf(cur_mon, fmt, ap);
+        return vfprintf(stderr, fmt, ap);
-    } else if (!cur_mon) {
-        vfprintf(stderr, fmt, ap);
     }
+    if (!monitor_cur_is_qmp()) {
+        return monitor_vprintf(cur_mon, fmt, ap);
+    }
+    return -1;
 }
 
 static void monitor_list_append(Monitor *mon)

stubs/error-printf.c

@@ -2,19 +2,22 @@
 #include "qemu-common.h"
 #include "qemu/error-report.h"
 
-void error_vprintf(const char *fmt, va_list ap)
+int error_vprintf(const char *fmt, va_list ap)
 {
+    int ret;
+
     if (g_test_initialized() && !g_test_subprocess() &&
         getenv("QTEST_SILENT_ERRORS")) {
         char *msg = g_strdup_vprintf(fmt, ap);
         g_test_message("%s", msg);
+        ret = strlen(msg);
         g_free(msg);
-    } else {
+        return ret;
-        vfprintf(stderr, fmt, ap);
     }
+    return vfprintf(stderr, fmt, ap);
 }
 
-void error_vprintf_unless_qmp(const char *fmt, va_list ap)
+int error_vprintf_unless_qmp(const char *fmt, va_list ap)
 {
-    error_vprintf(fmt, ap);
+    return error_vprintf(fmt, ap);
 }

util/qemu-error.c

@@ -24,22 +24,26 @@ typedef enum {
     REPORT_TYPE_INFO,
 } report_type;
 
-void error_printf(const char *fmt, ...)
+int error_printf(const char *fmt, ...)
 {
     va_list ap;
+    int ret;
 
     va_start(ap, fmt);
-    error_vprintf(fmt, ap);
+    ret = error_vprintf(fmt, ap);
     va_end(ap);
+    return ret;
 }
 
-void error_printf_unless_qmp(const char *fmt, ...)
+int error_printf_unless_qmp(const char *fmt, ...)
 {
     va_list ap;
+    int ret;
 
     va_start(ap, fmt);
-    error_vprintf_unless_qmp(fmt, ap);
+    ret = error_vprintf_unless_qmp(fmt, ap);
     va_end(ap);
+    return ret;
 }
 
 static Location std_loc = {