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

[Jason Wang]

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 <bro...@redhat.com> 
wrote:

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
[...]

@@ -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