Commit 5bdca94f authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Alexei Starovoitov
Browse files

bpf: Update bpf_design_QA.rst to clarify the kfunc call is not ABI 



This patch updates bpf_design_QA.rst to clarify that the kernel
function callable by bpf program is not an ABI.

Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20210330054150.2933542-1-kafai@fb.com
parent 7aae231a

Documentation/bpf/bpf_design_QA.rst

+15 −0
Original line number Diff line number Diff line
@@ -258,3 +258,18 @@ Q: Can BPF functionality such as new program or map types, new 
helpers, etc be added out of kernel module code?



A: NO.



Q: Directly calling kernel function is an ABI?

----------------------------------------------

Q: Some kernel functions (e.g. tcp_slow_start) can be called

by BPF programs.  Do these kernel functions become an ABI?



A: NO.



The kernel function protos will change and the bpf programs will be

rejected by the verifier.  Also, for example, some of the bpf-callable

kernel functions have already been used by other kernel tcp

cc (congestion-control) implementations.  If any of these kernel

functions has changed, both the in-tree and out-of-tree kernel tcp cc

implementations have to be changed.  The same goes for the bpf

programs and they have to be adjusted accordingly.