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, 4 insertions, 4 deletions

diff --git a/qemu-char.c b/qemu-char.c
index 84f49acbac..8575c54c98 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -3966,19 +3966,19 @@ void qemu_chr_fe_event(struct CharDriverState *chr, int event)
     }
 }
 
-int qemu_chr_fe_add_watch(CharDriverState *s, GIOCondition cond,
-                          GIOFunc func, void *user_data)
+guint qemu_chr_fe_add_watch(CharDriverState *s, GIOCondition cond,
+                            GIOFunc func, void *user_data)
 {
     GSource *src;
     guint tag;
 
     if (s->chr_add_watch == NULL) {
-        return -ENOSYS;
+        return 0;
     }
 
     src = s->chr_add_watch(s, cond);
     if (!src) {
-        return -EINVAL;
+        return 0;
     }
 
     g_source_set_callback(src, (GSourceFunc)func, user_data, NULL);