netdev - Re: [PATCH net-next 3/4] net/smc: Introduce smc_bpf

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Message-ID: <0e5712f2-7ecc-457a-afb7-4b304eb1bffa@linux.dev>
Date: Fri, 25 Oct 2024 11:30:10 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: "D. Wythe" <alibuda@...ux.alibaba.com>
Cc: kgraul@...ux.ibm.com, wenjia@...ux.ibm.com, jaka@...ux.ibm.com,
 ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, pabeni@...hat.com,
 song@...nel.org, sdf@...gle.com, haoluo@...gle.com, yhs@...com,
 edumazet@...gle.com, john.fastabend@...il.com, kpsingh@...nel.org,
 jolsa@...nel.org, guwen@...ux.alibaba.com, kuba@...nel.org,
 davem@...emloft.net, netdev@...r.kernel.org, linux-s390@...r.kernel.org,
 linux-rdma@...r.kernel.org, bpf@...r.kernel.org, dtcccc@...ux.alibaba.com
Subject: Re: [PATCH net-next 3/4] net/smc: Introduce smc_bpf_ops

On 10/25/24 4:05 AM, D. Wythe wrote:
> Our main concern is to avoid introducing kfuncs as much as possible. For our 
> subsystem, we might need to maintain it in a way that maintains a uapi, as we 
> certainly have user applications depending on it.

The smc_bpf_ops can read/write the tp and ireq. In patch 4, there is 
'tp->syn_smc = 1'. I assume the real bpf prog will read something from the tp to 
make the decision also. Note that tp/ireq is also not in the uapi but the CO-RE 
can help in case the tp->syn_smc bool is moved around.

 From looking at the selftest in patch 4 again, I think all it needs is for the 
bpf prog (i.e. the ops) to return a bool instead of allowing the bpf prog to 
write or call a kfunc to change the tp/ireq.