Re: [PATCH net] tuntap: add missing xdp flush

From: Jason Wang <redacted>
Date: Wed,  7 Feb 2018 17:14:46 +0800

When using devmap to redirect packets between interfaces,
xdp_do_flush() is usually a must to flush any batched
packets. Unfortunately this is missed in current tuntap
implementation.

Unlike most hardware driver which did XDP inside NAPI loop and call
xdp_do_flush() at then end of each round of poll. TAP did it in the
context of process e.g tun_get_user(). So fix this by count the
pending redirected packets and flush when it exceeds NAPI_POLL_WEIGHT
or MSG_MORE was cleared by sendmsg() caller.

With this fix, xdp_redirect_map works again between two TAPs.

Fixes: 761876c857cb ("tap: XDP support")
Signed-off-by: Jason Wang <redacted>

Applied and queued up for -stable, thanks Jason.