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authorMartin KaFai Lau <kafai@fb.com>2021-03-29 22:41:50 -0700
committerAlexei Starovoitov <ast@kernel.org>2021-03-30 07:31:01 -0700
commit5bdca94ff30d99168c3c09394da664c3c37c6834 (patch)
tree639f2bc7fe296402f20b3b9e0f164bc95dd3e005 /Documentation/bpf
parent7aae231ac93b9d9c45487dcafd844fa756069f3b (diff)
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: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20210330054150.2933542-1-kafai@fb.com
Diffstat (limited to 'Documentation/bpf')
-rw-r--r--Documentation/bpf/bpf_design_QA.rst15
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/bpf/bpf_design_QA.rst b/Documentation/bpf/bpf_design_QA.rst
index 0e15f9b05c9d..437de2a7a5de 100644
--- a/Documentation/bpf/bpf_design_QA.rst
+++ b/Documentation/bpf/bpf_design_QA.rst
@@ -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.