If qemu_chr_write_buffer() returned an error, but could
write some characters, return the number of character
written. Otherwise frontends able to recover and resume
writes re-write the partial chars already written.

Cc: qemu-stable@nongnu.org
Suggested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 chardev/char.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/chardev/char.c b/chardev/char.c
index 30b21fedce4..5c8130b2435 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -189,7 +189,7 @@ int qemu_chr_write(Chardev *s, const uint8_t *buf, int len, bool write_all)
         replay_char_write_event_save(res, offset);
     }
 
-    if (res < 0) {
+    if (res < 0 && offset == 0) {
         return res;
     }
     return offset;
-- 
2.51.0