[PATCH net-next V2 05/11] tuntap: tweak on the path of skb XDP case in tun_build_skb()

Jason Wang
2018-09-12T03:17:03Z

If we're sure not to go native XDP, there's no need for several things
like bh and rcu stuffs. So this patch introduces a helper to build skb
and hold page refcnt. When we found we will go through skb path, build
skb directly.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/net/tun.c | 39 ++++++++++++++++++++++++---------------
1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 257cf7342d54..946c6148ed75 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1635,6 +1635,23 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
return true;
}

+static struct sk_buff *__tun_build_skb(struct page_frag *alloc_frag, char *buf,
+ int buflen, int len, int pad, int delta)
+{
+ struct sk_buff *skb = build_skb(buf, buflen);
+
+ if (!skb)
+ return ERR_PTR(-ENOMEM);
+
+ skb_reserve(skb, pad - delta);
+ skb_put(skb, len);
+
+ get_page(alloc_frag->page);
+ alloc_frag->offset += buflen;
+
+ return skb;
+}
+
static struct sk_buff *tun_build_skb(struct tun_struct *tun,
struct tun_file *tfile,
struct iov_iter *from,
@@ -1642,7 +1659,6 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
int len, int *skb_xdp)
{
struct page_frag *alloc_frag = &current->task_frag;
- struct sk_buff *skb;
struct bpf_prog *xdp_prog;
int buflen = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
unsigned int delta = 0;
@@ -1672,10 +1688,12 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
* of xdp_prog above, this should be rare and for simplicity
* we do XDP on skb in case the headroom is not enough.
*/
- if (hdr->gso_type || !xdp_prog)
+ if (hdr->gso_type || !xdp_prog) {
*skb_xdp = 1;
- else
- *skb_xdp = 0;
+ return __tun_build_skb(alloc_frag, buf, buflen, len, pad, delta);
+ }
+
+ *skb_xdp = 0;

local_bh_disable();
rcu_read_lock();
@@ -1719,22 +1737,13 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
trace_xdp_exception(tun->dev, xdp_prog, act);
/* fall through */
case XDP_DROP:
- goto err_xdp;
+ goto out;
}
}
rcu_read_unlock();
local_bh_enable();

- skb = build_skb(buf, buflen);
- if (!skb)
- return ERR_PTR(-ENOMEM);
-
- skb_reserve(skb, pad - delta);
- skb_put(skb, len);
- get_page(alloc_frag->page);
- alloc_frag->offset += buflen;
-
- return skb;
+ return __tun_build_skb(alloc_frag, buf, buflen, len, pad, delta);

err_redirect:
put_page(alloc_frag->page);
--
2.17.1