Hi
On Thu, Dec 3, 2015 at 10:53 AM, Didier Pallard
<didier.pall...@6wind.com> wrote:
> unix_send_msgfds is used by vhost-user control socket. qemu_chr_fe_write_all
> is used to send a message and retries as long as EAGAIN errno is set,
> but write_msgfds buffer is freed after first EAGAIN failure, causing
> message to be sent without proper fds attachment.
>
> In case unix_send_msgfds is called through qemu_chr_fe_write, it will be
> user responsability to resend message as is or to free write_msgfds
> using set_msgfds(0)
>
> Signed-off-by: Didier Pallard <didier.pall...@6wind.com>
> Reviewed-by: Thibaut Collet <thibaut.col...@6wind.com>
> ---
> qemu-char.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/qemu-char.c b/qemu-char.c
> index 5448b0f..26d5f2e 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -2614,6 +2614,16 @@ static int unix_send_msgfds(CharDriverState *chr,
> const uint8_t *buf, int len)
> r = sendmsg(s->fd, &msgh, 0);
> } while (r < 0 && errno == EINTR);
>
> + /* Ancillary data are not sent if no byte is written
> + * so don't free msgfds buffer if return value is EAGAIN
> + * If called from qemu_chr_fe_write_all retry will come soon
> + * If called from qemu_chr_fe_write, it is the user responsibility
> + * to resend message or free fds using set_msgfds(0)
> + */
> + if (r < 0 && errno == EAGAIN) {
> + return r;
> + }
> +
This looks reasonable to me. However, I don't know what happens with
partial write of ancillary data. Hopefully it's all or nothing.
Apparently, reading unix_stream_sendmsg() in kernel shows that as long
as a few bytes have been sent, the ancillary data is sent. So it looks
like it still does the right thing in case of a partial write.
Reviewed-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> /* free the written msgfds, no matter what */
> if (s->write_msgfds_num) {
> g_free(s->write_msgfds);
> --
> 2.1.4
>
>
--
Marc-André Lureau
