| Message ID | 20210330054150.2933542-1-kafai@fb.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | BPF |
| Headers | show |
| Series | bpf: Update doc about calling kernel function | expand |
| Context | Check | Description |
|---|---|---|
| netdev/cover_letter | success | Link |
| netdev/fixes_present | success | Link |
| netdev/patch_count | success | Link |
| netdev/tree_selection | success | Clearly marked for bpf-next |
| netdev/subject_prefix | success | Link |
| netdev/cc_maintainers | warning | 7 maintainers not CCed: yhs@fb.com kpsingh@kernel.org andrii@kernel.org linux-doc@vger.kernel.org john.fastabend@gmail.com corbet@lwn.net songliubraving@fb.com |
| netdev/source_inline | success | Was 0 now: 0 |
| netdev/verify_signedoff | success | Link |
| netdev/module_param | success | Was 0 now: 0 |
| netdev/build_32bit | success | Errors and warnings before: 0 this patch: 0 |
| netdev/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| netdev/verify_fixes | success | Link |
| netdev/checkpatch | success | total: 0 errors, 0 warnings, 0 checks, 18 lines checked |
| netdev/build_allmodconfig_warn | success | Errors and warnings before: 0 this patch: 0 |
| netdev/header_inline | success | Link |
> On Mar 29, 2021, at 10:41 PM, Martin KaFai Lau <kafai@fb.com> wrote: > > 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> Acked-by: Song Liu <songliubraving@fb.com>
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.
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> --- Documentation/bpf/bpf_design_QA.rst | 15 +++++++++++++++ 1 file changed, 15 insertions(+)