Hi all, I don't think that checking DF flag is a case for figuring out that the packet is a fragment of some big datagram. For nonfragmented packets, DF may not be set. We need to check that the fragment offset is 0. Actually, it's a good idea to check that MF flag is not set too. So we can find the first fragment that doesn't require steering. So the code may look something like this: ``` info->is_fragmented = !!(bpf_ntohs(ip.frag_off) & (0x2000 | 0x1fff)); // checking MF and frag offset. OR info->is_fragmented = !!(bpf_ntohs(ip.frag_off) & ~0x4000); // if we consider that CE always 0(which is always should be) ```
On Sun, Apr 23, 2023 at 9:12 AM Yan Vugenfirer <yvuge...@redhat.com> wrote: > > FYI > > ---------- Forwarded message --------- > From: luwenpeng <lwp_1...@163.com> > Date: Fri, Apr 21, 2023 at 3:21 PM > Subject: [PATCH] tools/ebpf: Fix IPv4 fragmentation identify > To: <qemu-devel@nongnu.org> > Cc: <jasow...@redhat.com>, luwenpeng <lwp_1...@163.com> > > > The meaning of the bit flag in ip.frag_off is Don`t fragmented > When judging IPv4 is_fragmented according to ip.frag_off, > should use !(bpf_ntohs(ip.frag_off) & 0x4000) instead of !!ip.frag_off > > Signed-off-by: WenPeng Lu <lwp_1...@163.com> > --- > tools/ebpf/rss.bpf.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/ebpf/rss.bpf.c b/tools/ebpf/rss.bpf.c > index 20f227e2ac..e77b764f3d 100644 > --- a/tools/ebpf/rss.bpf.c > +++ b/tools/ebpf/rss.bpf.c > @@ -317,7 +317,7 @@ static inline int parse_packet(struct __sk_buff *skb, > > info->in_src = ip.saddr; > info->in_dst = ip.daddr; > - info->is_fragmented = !!ip.frag_off; > + info->is_fragmented = !(bpf_ntohs(ip.frag_off) & 0x4000); > > l4_protocol = ip.protocol; > l4_offset = ip.ihl * 4; > -- > 2.30.1 (Apple Git-130) > >
