Re: [PATCH net-next 06/11] tuntap: split out XDP logic

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On 2018年09月07日 01:21, Michael S. Tsirkin wrote:
On Thu, Sep 06, 2018 at 12:05:21PM +0800, Jason Wang wrote:
This patch split out XDP logic into a single function. This make it to
be reused by XDP batching path in the following patch.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
  drivers/net/tun.c | 84 ++++++++++++++++++++++++++++-------------------
  1 file changed, 51 insertions(+), 33 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 389aa0727cc6..21b125020b3b 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1635,6 +1635,44 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
  	return true;
  }
+static u32 tun_do_xdp(struct tun_struct *tun,
+		      struct tun_file *tfile,
+		      struct bpf_prog *xdp_prog,
+		      struct xdp_buff *xdp,
+		      int *err)
+{
+	u32 act = bpf_prog_run_xdp(xdp_prog, xdp);
+
+	switch (act) {
+	case XDP_REDIRECT:
+		*err = xdp_do_redirect(tun->dev, xdp, xdp_prog);
+		xdp_do_flush_map();
+		if (*err)
+			break;
+		goto out;
+	case XDP_TX:
+		*err = tun_xdp_tx(tun->dev, xdp);
+		if (*err < 0)
+			break;
+		*err = 0;
+		goto out;
+	case XDP_PASS:
+		goto out;
Do we need goto? why not just return?

I don't see any difference.


+	default:
+		bpf_warn_invalid_xdp_action(act);
+		/* fall through */
+	case XDP_ABORTED:
+		trace_xdp_exception(tun->dev, xdp_prog, act);
+		/* fall through */
+	case XDP_DROP:
+		break;
+	}
+
+	put_page(virt_to_head_page(xdp->data_hard_start));
put here because caller does get_page :( Not pretty.
I'd move this out to the caller.

Then we need a switch in the caller, not sure it's better.


+out:
+	return act;
How about combining err and act? err is < 0 XDP_PASS is > 0.
No need for pointers then.

Ok.


+}
+
  static struct sk_buff *tun_build_skb(struct tun_struct *tun,
  				     struct tun_file *tfile,
  				     struct iov_iter *from,
@@ -1645,10 +1683,10 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
  	struct sk_buff *skb = NULL;
  	struct bpf_prog *xdp_prog;
  	int buflen = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
-	unsigned int delta = 0;
  	char *buf;
  	size_t copied;
-	int err, pad = TUN_RX_PAD;
+	int pad = TUN_RX_PAD;
+	int err = 0;
rcu_read_lock();
  	xdp_prog = rcu_dereference(tun->xdp_prog);
@@ -1685,9 +1723,8 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
  	local_bh_disable();
  	rcu_read_lock();
  	xdp_prog = rcu_dereference(tun->xdp_prog);
-	if (xdp_prog && !*skb_xdp) {
+	if (xdp_prog) {
  		struct xdp_buff xdp;
-		void *orig_data;
  		u32 act;
xdp.data_hard_start = buf;
@@ -1695,33 +1732,14 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
  		xdp_set_data_meta_invalid(&xdp);
  		xdp.data_end = xdp.data + len;
  		xdp.rxq = &tfile->xdp_rxq;
-		orig_data = xdp.data;
-		act = bpf_prog_run_xdp(xdp_prog, &xdp);
-
-		switch (act) {
-		case XDP_REDIRECT:
-			err = xdp_do_redirect(tun->dev, &xdp, xdp_prog);
-			xdp_do_flush_map();
-			if (err)
-				goto err_xdp;
-			goto out;
-		case XDP_TX:
-			if (tun_xdp_tx(tun->dev, &xdp) < 0)
-				goto err_xdp;
-			goto out;
-		case XDP_PASS:
-			delta = orig_data - xdp.data;
-			len = xdp.data_end - xdp.data;
-			break;
-		default:
-			bpf_warn_invalid_xdp_action(act);
-			/* fall through */
-		case XDP_ABORTED:
-			trace_xdp_exception(tun->dev, xdp_prog, act);
-			/* fall through */
-		case XDP_DROP:
+		act = tun_do_xdp(tun, tfile, xdp_prog, &xdp, &err);
+		if (err)
  			goto err_xdp;
-		}
+		if (act != XDP_PASS)
+			goto out;
likely?

It depends on the XDP program, so I tend not to use it.


+
+		pad = xdp.data - xdp.data_hard_start;
+		len = xdp.data_end - xdp.data;
  	}
  	rcu_read_unlock();
  	local_bh_enable();
@@ -1729,18 +1747,18 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
  build:
  	skb = build_skb(buf, buflen);
  	if (!skb) {
+		put_page(alloc_frag->page);
  		skb = ERR_PTR(-ENOMEM);
  		goto out;
  	}
- skb_reserve(skb, pad - delta);
+	skb_reserve(skb, pad);
  	skb_put(skb, len);
return skb; err_xdp:
-	alloc_frag->offset -= buflen;
-	put_page(alloc_frag->page);
+	this_cpu_inc(tun->pcpu_stats->rx_dropped);

This fixes bug in previous patch which dropped it. OK :)

Yes, but let me move this to the buggy patch.

Thanks

  out:
  	rcu_read_unlock();
  	local_bh_enable();
--
2.17.1




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