On Mon, Jul 3, 2023 at 4:45 PM David Ahern <dsahern@xxxxxxxxxx> wrote: > > On 7/3/23 12:22 AM, Mina Almasry wrote: > > tcpdump is able to access the header of these skbs which is in host > > memory, but not the payload in device memory. Here is an example > > session with my netcat-like test for device memory TCP: > > https://pastebin.com/raw/FRjKf0kv > > > > tcpdump seems to work, and the length of the packets above is correct. > > tcpdump -A however isn't able to print the payload of the packets: > > https://pastebin.com/raw/2PcNxaZV > > That is my expectation. The tcpdump is just an easy example of accessing > the skb page frags. skb_copy_and_csum_bits used by icmp is another > example that can walk frags wanting access to device memory. You did not > cause a panic or trip a WARN_ON for example with the tcpdump? > Change for af_packet was not too hard :) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index a2dbeb264f260e5b8923ece9aac99fe19ddfeb62..aa4133d1b1e0676e408499ea4534b51262394432 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -2152,7 +2152,7 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev, } } - snaplen = skb->len; + snaplen = skb->devmem ? skb_headlen(skb) : skb->len; res = run_filter(skb, sk, snaplen); if (!res) @@ -2275,7 +2275,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, } } - snaplen = skb->len; + snaplen = skb->devmem ? skb_headlen(skb) : skb->len; res = run_filter(skb, sk, snaplen); if (!res) And a generic change in pskb_may_pull() ( __pskb_pull_tail() more exactly) was enough to cover most other cases.
