serial: poll the serial console with G_IO_HUP

On FreeBSD polling a master pty while the other end is not connected
with G_IO_OUT only results in an endless wait. This is different from
the Linux behaviour, that returns immediately. In order to demonstrate
this, I have the following example code:

http://xenbits.xen.org/people/royger/test_poll.c

When executed on Linux:

$ ./test_poll
In callback

On FreeBSD instead, the callback never gets called:

$ ./test_poll

So, in order to workaround this, poll the source with G_IO_HUP (which
makes the code behave the same way on both Linux and FreeBSD).
Signed-off-by: NRoger Pau Monné <roger.pau@citrix.com>
Cc: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Cc: Michael Tokarev <mjt@tls.msk.ru>
Cc: "Andreas Färber" <afaerber@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: xen-devel@lists.xenproject.org
[Add hw/char/cadence_uart.c too. - Paolo]
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/char/cadence_uart.c

@@ -306,7 +306,8 @@ static gboolean cadence_uart_xmit(GIOChannel *chan, GIOCondition cond,
     memmove(s->tx_fifo, s->tx_fifo + ret, s->tx_count);
 
     if (s->tx_count) {
-        int r = qemu_chr_fe_add_watch(s->chr, G_IO_OUT, cadence_uart_xmit, s);
+        int r = qemu_chr_fe_add_watch(s->chr, G_IO_OUT|G_IO_HUP,
+                                      cadence_uart_xmit, s);
         assert(r);
     }
 

hw/char/serial.c

@@ -246,7 +246,7 @@ static gboolean serial_xmit(GIOChannel *chan, GIOCondition cond, void *opaque)
         serial_receive1(s, &s->tsr, 1);
     } else if (qemu_chr_fe_write(s->chr, &s->tsr, 1) != 1) {
         if (s->tsr_retry >= 0 && s->tsr_retry < MAX_XMIT_RETRY &&
-            qemu_chr_fe_add_watch(s->chr, G_IO_OUT, serial_xmit, s) > 0) {
+            qemu_chr_fe_add_watch(s->chr, G_IO_OUT|G_IO_HUP, serial_xmit, s) > 0) {
             s->tsr_retry++;
             return FALSE;
         }

hw/char/virtio-console.c

@@ -70,7 +70,8 @@ static ssize_t flush_buf(VirtIOSerialPort *port,
         if (!k->is_console) {
             virtio_serial_throttle_port(port, true);
             if (!vcon->watch) {
-                vcon->watch = qemu_chr_fe_add_watch(vcon->chr, G_IO_OUT,
+                vcon->watch = qemu_chr_fe_add_watch(vcon->chr,
+                                                    G_IO_OUT|G_IO_HUP,
                                                     chr_write_unblocked, vcon);
             }
         }

hw/usb/redirect.c

@@ -290,7 +290,7 @@ static int usbredir_write(void *priv, uint8_t *data, int count)
     r = qemu_chr_fe_write(dev->cs, data, count);
     if (r < count) {
         if (!dev->watch) {
-            dev->watch = qemu_chr_fe_add_watch(dev->cs, G_IO_OUT,
+            dev->watch = qemu_chr_fe_add_watch(dev->cs, G_IO_OUT|G_IO_HUP,
                                                usbredir_write_unblocked, dev);
         }
         if (r < 0) {

monitor.c

@@ -321,7 +321,7 @@ static void monitor_flush_locked(Monitor *mon)
             mon->outbuf = tmp;
         }
         if (mon->out_watch == 0) {
-            mon->out_watch = qemu_chr_fe_add_watch(mon->chr, G_IO_OUT,
+            mon->out_watch = qemu_chr_fe_add_watch(mon->chr, G_IO_OUT|G_IO_HUP,
                                                    monitor_unblocked, mon);
         }
     }