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| author | Martin KaFai Lau <kafai@fb.com> | 2021-03-30 07:41:50 +0200 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2021-03-30 16:31:01 +0200 |
| commit | 5bdca94ff30d99168c3c09394da664c3c37c6834 (patch) | |
| tree | 639f2bc7fe296402f20b3b9e0f164bc95dd3e005 /Documentation/bpf/bpf_design_QA.rst | |
| parent | bpf: tcp: Limit calling some tcp cc functions to CONFIG_DYNAMIC_FTRACE (diff) | |
| download | linux-5bdca94ff30d99168c3c09394da664c3c37c6834.tar.xz linux-5bdca94ff30d99168c3c09394da664c3c37c6834.zip | |
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/bpf_design_QA.rst')
| -rw-r--r-- | Documentation/bpf/bpf_design_QA.rst | 15 |
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. |