char: change qemu_chr_fe_add_watch to return unsigned

g_source_attach can return any value between 1 and UINT_MAX if you let
QEMU run long enough.  However, qemu_chr_fe_add_watch can also return
a negative errno value when the device is disconnected or does not
support chr_add_watch.  Change it to return zero to avoid overloading
these values.

Fix the cadence_uart which asserts in this case (easily obtained with
"-serial pty").

Tested-by: Bret Ketchum <bcketchum@gmail.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
index c856fc30b2..65179fa500 100644
--- a/hw/char/cadence_uart.c
+++ b/hw/char/cadence_uart.c
@@ -292,9 +292,12 @@ 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|G_IO_HUP,
-                                      cadence_uart_xmit, s);
-        assert(r);
+        guint r = qemu_chr_fe_add_watch(s->chr, G_IO_OUT|G_IO_HUP,
+                                        cadence_uart_xmit, s);
+        if (!r) {
+            s->tx_count = 0;
+            return FALSE;
+        }
     }
 
     uart_update_status(s);