[vlc-devel] [PATCH 3/3] access/udp: reduce mtu amount on initial packets

[Ilkka Ollakka]

On Mon, Oct 15, 2018 at 09:30:53PM +0300, Ilkka Ollakka wrote:
> In this approach, mtu is setted to high on start, and if received data
> is less than 1500 and mtu is higher than that, we adjust mtu on future
> packets to be smaller. In majority of cases in UDP streaming, packet
> size is usually quite constant, so it should work, even if it's not
> generic solution to udp packet receiving.
> 
> Also in case of truncing packets on other than linux systems, use same
> assumption and peek the next data amount to adjust mtu for future
> packets. We don't call PEEK on all the cases, as it would be unnecessary
> system call on majority of the calls.
> 
> ref #20952 and other similar tickets.
> ---
>  modules/access/udp.c | 40 +++++++++++++++++++++++++++++++++++++---
>  1 file changed, 37 insertions(+), 3 deletions(-)
> +#ifdef __linux__
>          msg_Err(access, "%zd bytes packet truncated (MTU was %zu)",
>                  len, sys->mtu);
> -        pkt->i_flags |= BLOCK_FLAG_CORRUPTED;
>          sys->mtu = len;
> +#else
> +        sys->mtu = recv(sys->fd, pkt->p_buffer, sys->mtu, MSG_PEEK|MSG_TRUNC);

This ofcourse requires separated temporary buffer/size, so we don't overwrite already
received and corrupted packet. But I'll fix that if the approach seems valid.

> +        /* In this case, len is old mtu and max received amount, mtu is the
> +         * peeked value, that's why they are otherway around in this compared
> +         * to __linux__ case error
> +         */
> +        msg_Err(access, "%zd bytes packet truncated (MTU was %zu)",
> +                sys->mtu, len);
> +#endif
>      }
>      else
> +#endif
>          pkt->i_buffer = len;
>  
>      return pkt;
> -- 
> 2.19.0
> 

-- 
Ilkka Ollakka