ui/console-vc: report to the application instead of screen rendering

Terminal Device Status Report (DSR) [1] should be sent to an
application, not rendered to the screen. This patch fixes rendering of
terminal report, which appear only on the graphical screen of the
terminal (console "vc") and can be reproduced by the following
command:

     echo -en '\e[6n'; IFS='[;' read -sdR _ row col; echo $row:$col

Command requests cursor position and waits for terminal response, but
instead, the response is rendered to the graphical screen and never
sent to an application.

Why bother? Busybox shell (ash) in Alpine distribution requests cursor
position on each shell prompt (once <ENTER> is pressed), which makes a
prompt on a graphical screen corrupted with repeating Cursor Position
Report (CPR) [2]:

   [root@alpine ~]# \033[57;1R]

Which is very annoying and incorrect.

[1] https://vt100.net/docs/vt100-ug/chapter3.html#DSR
[2] https://vt100.net/docs/vt100-ug/chapter3.html#CPR

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20250226075913.353676-3-r.peniaev@gmail.com>

diff --git a/ui/console-vc.c b/ui/console-vc.c
index 90ff0ffda8c50ec4d0be1703cf33accb05cf9869..d512f57e10a9e58c0e107558562be5264306273e 100644 (file)
--- a/ui/console-vc.c
+++ b/ui/console-vc.c
@@ -617,10 +617,9 @@ static void vc_put_one(VCChardev *vc, int ch)
 
 static void vc_respond_str(VCChardev *vc, const char *buf)
 {
-    while (*buf) {
-        vc_put_one(vc, *buf);
-        buf++;
-    }
+    QemuTextConsole *s = vc->console;
+
+    qemu_chr_be_write(s->chr, (const uint8_t *)buf, strlen(buf));
 }
 
 /* set cursor, checking bounds */