Re: [bpf-next V2 PATCH 06/15] tun: convert to use generic xdp_frame and xdp_return_frame API

On 2018年03月08日 23:16, Jesper Dangaard Brouer wrote:

Hi Jason,

Please see below FIXME, which is actually a question to you.

On Thu, 08 Mar 2018 14:08:11 +0100 Jesper Dangaard Brouer [off-list ref] wrote:

quoted

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 475088f947bb..cd046cf31b77 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

[...]

quoted

@@ -1290,17 +1290,18 @@ static const struct net_device_ops tun_netdev_ops = {
  static int tun_xdp_xmit(struct net_device *dev, struct xdp_buff *xdp)
  {
  	struct tun_struct *tun = netdev_priv(dev);
-	struct xdp_buff *buff = xdp->data_hard_start;
-	int headroom = xdp->data - xdp->data_hard_start;
+	struct xdp_frame *frame;
  	struct tun_file *tfile;
  	u32 numqueues;
  	int ret = 0;
  
-	/* Assure headroom is available and buff is properly aligned */
-	if (unlikely(headroom < sizeof(*xdp) || tun_is_xdp_buff(xdp)))
-		return -ENOSPC;
+	/* FIXME: Explain why this check is the needed! */
+	if (unlikely(tun_is_xdp_frame(xdp)))
+		return -EBADRQC;
  
-	*buff = *xdp;
+	frame = convert_to_xdp_frame(xdp);
+	if (unlikely(!frame))
+		return -EOVERFLOW;

To Jason, in the FIXME, I'm inheriting a check you put in, but I don't
understand why this check was needed?

Sorry for the late reply.

I think it was used to make sure to not use misaligned or invalid pointer that caller passed to us.

Thanks