Re: [PATCH v3 1/3] QIOChannelSocket: Fix zero-copy flush returning code 1 when nothing sent

[Peter Xu]

Hi, Leo,

On Mon, Jul 04, 2022 at 05:23:13PM -0300, Leonardo Bras wrote:
> If flush is called when no buffer was sent with MSG_ZEROCOPY, it currently
> returns 1. This return code should be used only when Linux fails to use
> MSG_ZEROCOPY on a lot of sendmsg().
> 
> Fix this by returning early from flush if no sendmsg(...,MSG_ZEROCOPY)
> was attempted.
> 
> Fixes: 2bc58ffc2926 ("QIOChannelSocket: Implement io_writev zero copy flag & 
> io_flush for CONFIG_LINUX")
> Signed-off-by: Leonardo Bras <leobras@redhat.com>
> ---
>  io/channel-socket.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/io/channel-socket.c b/io/channel-socket.c
> index 4466bb1cd4..698c086b70 100644
> --- a/io/channel-socket.c
> +++ b/io/channel-socket.c
> @@ -716,12 +716,18 @@ static int qio_channel_socket_flush(QIOChannel *ioc,
>      struct cmsghdr *cm;
>      char control[CMSG_SPACE(sizeof(*serr))];
>      int received;
> -    int ret = 1;
> +    int ret;
> +
> +    if (!sioc->zero_copy_queued) {

I think I asked this in the downstream review but didn't get a
response.. shouldn't this check be "queued == sent"?

> +        return 0;
> +    }
>  
>      msg.msg_control = control;
>      msg.msg_controllen = sizeof(control);
>      memset(control, 0, sizeof(control));
>  
> +    ret = 1;
> +
>      while (sioc->zero_copy_sent < sioc->zero_copy_queued) {
>          received = recvmsg(sioc->fd, &msg, MSG_ERRQUEUE);
>          if (received < 0) {
> -- 
> 2.36.1
> 

-- 
Peter Xu