virtio-console: Also throttle when less was written then requested

This is necessary so that we get properly woken up to write the rest.

This patch also changes the len argument to the have_data callback, to
avoid doing an unsigned signed comparison.
Signed-off-by: NHans de Goede <hdegoede@redhat.com>
Acked-by: NAmit Shah <amit.shah@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/char/virtio-console.c

@@ -34,7 +34,8 @@ static gboolean chr_write_unblocked(GIOChannel *chan, GIOCondition cond,
 }
 
 /* Callback function that's called when the guest sends us data */
-static ssize_t flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
+static ssize_t flush_buf(VirtIOSerialPort *port,
+                         const uint8_t *buf, ssize_t len)
 {
     VirtConsole *vcon = DO_UPCAST(VirtConsole, port, port);
     ssize_t ret;
@@ -47,7 +48,7 @@ static ssize_t flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
     ret = qemu_chr_fe_write(vcon->chr, buf, len);
     trace_virtio_console_flush_buf(port->id, len, ret);
 
-    if (ret <= 0) {
+    if (ret < len) {
         VirtIOSerialPortClass *k = VIRTIO_SERIAL_PORT_GET_CLASS(port);
 
         /*
@@ -56,7 +57,8 @@ static ssize_t flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
          * we had a finer-grained message, like -EPIPE, we could close
          * this connection.
          */
-        ret = 0;
+        if (ret < 0)
+            ret = 0;
         if (!k->is_console) {
             virtio_serial_throttle_port(port, true);
             qemu_chr_fe_add_watch(vcon->chr, G_IO_OUT, chr_write_unblocked,

include/hw/virtio/virtio-serial.h

@@ -104,7 +104,7 @@ typedef struct VirtIOSerialPortClass {
      * 'len'.  In this case, throttling will be enabled for this port.
      */
     ssize_t (*have_data)(VirtIOSerialPort *port, const uint8_t *buf,
-                         size_t len);
+                         ssize_t len);
 } VirtIOSerialPortClass;
 
 /*