From: Florian Westphal <fw@strlen.de>
To: Huajian Yang <huajianyang@asrmicro.com>
Cc: pablo@netfilter.org, kadlec@netfilter.org, razor@blackwall.org,
idosch@nvidia.com, davem@davemloft.net, dsahern@kernel.org,
edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
horms@kernel.org, netfilter-devel@vger.kernel.org,
coreteam@netfilter.org, bridge@lists.linux.dev,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] net: Expand headroom to send fragmented packets in bridge fragment forward
Date: Wed, 9 Apr 2025 11:18:21 +0200 [thread overview]
Message-ID: <20250409091821.GA17911@breakpoint.cc> (raw)
In-Reply-To: <20250409073336.31996-1-huajianyang@asrmicro.com>
Huajian Yang <huajianyang@asrmicro.com> wrote:
> The config NF_CONNTRACK_BRIDGE will change the way fragments are processed.
> Bridge does not know that it is a fragmented packet and forwards it
> directly, after NF_CONNTRACK_BRIDGE is enabled, function nf_br_ip_fragment
> will check and fraglist this packet.
>
> Some network devices that would not able to ping large packet under bridge,
> but large packet ping is successful if not enable NF_CONNTRACK_BRIDGE.
Can you add a new test to tools/testing/selftests/net/netfilter/ that
demonstrates this problem?
> In function nf_br_ip_fragment, checking the headroom before sending is
> undoubted, but it is unreasonable to directly drop skb with insufficient
> headroom.
Are we talking about
if (first_len - hlen > mtu
or
skb_headroom(skb) < ll_rs)
?
>
> if (first_len - hlen > mtu ||
> skb_headroom(skb) < ll_rs)
> - goto blackhole;
> + goto expand_headroom;
I guess this should be
if (first_len - hlen > mtu)
goto blackhole;
if (skb_headroom(skb) < ll_rs)
goto expand_headroom;
... but I'm not sure what the actual problem is.
> +expand_headroom:
> + struct sk_buff *expand_skb;
> +
> + expand_skb = skb_copy_expand(skb, ll_rs, skb_tailroom(skb), GFP_ATOMIC);
> + if (unlikely(!expand_skb))
> + goto blackhole;
Why does this need to make a full skb copy?
Should that be using skb_expand_head()?
> slow_path:
Actually, can't you just (re)use the slowpath for the skb_headroom < ll_rs
case instead of adding headroom expansion?
next prev parent reply other threads:[~2025-04-09 9:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-09 7:33 [PATCH] net: Expand headroom to send fragmented packets in bridge fragment forward Huajian Yang
2025-04-09 9:18 ` Florian Westphal [this message]
2025-04-09 10:27 ` 答复: " Yang Huajian（杨华健）
2025-04-09 10:45 ` Florian Westphal
-- strict thread matches above, loose matches on Subject: below --
2025-04-09 7:44 Huajian Yang
2025-04-11 10:54 ` Simon Horman
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