qemu_chr_write() dispatches to ChardevClass::chr_write(),
and is expected to propagate the backend error, not some
unrelated one produce by "best effort" logfile or replay.
Preserve and return the relevant %errno.

Cc: qemu-stable@nongnu.org
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 chardev/char.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/chardev/char.c b/chardev/char.c
index 7931f4e0832..46a2dbfb5a3 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -114,6 +114,7 @@ static int qemu_chr_write_buffer(Chardev *s,
                                  int *offset, bool write_all)
 {
     ChardevClass *cc = CHARDEV_GET_CLASS(s);
+    int saved_errno;
     int res = 0;
     *offset = 0;
 
@@ -139,6 +140,7 @@ static int qemu_chr_write_buffer(Chardev *s,
             break;
         }
     }
+    saved_errno = errno;
     if (*offset > 0) {
         /*
          * If some data was written by backend, we should
@@ -156,6 +158,7 @@ static int qemu_chr_write_buffer(Chardev *s,
         qemu_chr_write_log(s, buf, len);
     }
     qemu_mutex_unlock(&s->chr_write_lock);
+    errno = saved_errno;
 
     return res;
 }
@@ -192,7 +195,9 @@ int qemu_chr_write(Chardev *s, const uint8_t *buf, int len, bool write_all)
     }
 
     if (qemu_chr_replay(s) && replay_mode == REPLAY_MODE_RECORD) {
+        int saved_errno = errno;
         replay_char_write_event_save(res, offset);
+        errno = saved_errno;
     }
 
     if (res < 0) {
-- 
2.51.0