chardev: block during sync read

A sync read should block until all requested data is
available (instead of retrying in qemu_chr_fe_read_all). Change the
channel to blocking during sync_read.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20170706170353.32601-1-marcandre.lureau@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>

chardev/char-socket.c

@@ -454,7 +454,9 @@ static int tcp_chr_sync_read(Chardev *chr, const uint8_t *buf, int len)
         return 0;
     }
 
+    qio_channel_set_blocking(s->ioc, true, NULL);
     size = tcp_chr_recv(chr, (void *) buf, len);
+    qio_channel_set_blocking(s->ioc, false, NULL);
     if (size == 0) {
         /* connection closed */
         tcp_chr_disconnect(chr);