* [PATCH bpf-next 0/2] bpf: Update doc about calling kernel function
@ 2021-03-30 5:41 Martin KaFai Lau
2021-03-30 5:41 ` [PATCH bpf-next 1/2] bpf: Update bpf_design_QA.rst to clarify the kfunc call is not ABI Martin KaFai Lau
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Martin KaFai Lau @ 2021-03-30 5:41 UTC (permalink / raw)
To: bpf; +Cc: Alexei Starovoitov, Daniel Borkmann, kernel-team, netdev
This set updates the document about the bpf program calling kernel
function. In particular, updates are regarding to the clang
requirement in selftests and kfunc-call not an ABI.
Martin KaFai Lau (2):
bpf: Update bpf_design_QA.rst to clarify the kfunc call is not ABI
bpf: selftests: Update clang requirement in README.rst for testing
kfunc call
Documentation/bpf/bpf_design_QA.rst | 15 +++++++++++++++
tools/testing/selftests/bpf/README.rst | 14 ++++++++++++++
2 files changed, 29 insertions(+)
--
2.30.2
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH bpf-next 1/2] bpf: Update bpf_design_QA.rst to clarify the kfunc call is not ABI
2021-03-30 5:41 [PATCH bpf-next 0/2] bpf: Update doc about calling kernel function Martin KaFai Lau
@ 2021-03-30 5:41 ` Martin KaFai Lau
2021-03-30 6:40 ` Song Liu
2021-03-30 5:41 ` [PATCH bpf-next 2/2] bpf: selftests: Update clang requirement in README.rst for testing kfunc call Martin KaFai Lau
2021-03-30 16:33 ` [PATCH bpf-next 0/2] bpf: Update doc about calling kernel function Alexei Starovoitov
2 siblings, 1 reply; 6+ messages in thread
From: Martin KaFai Lau @ 2021-03-30 5:41 UTC (permalink / raw)
To: bpf; +Cc: Alexei Starovoitov, Daniel Borkmann, kernel-team, netdev
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(+)
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.
--
2.30.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH bpf-next 2/2] bpf: selftests: Update clang requirement in README.rst for testing kfunc call
2021-03-30 5:41 [PATCH bpf-next 0/2] bpf: Update doc about calling kernel function Martin KaFai Lau
2021-03-30 5:41 ` [PATCH bpf-next 1/2] bpf: Update bpf_design_QA.rst to clarify the kfunc call is not ABI Martin KaFai Lau
@ 2021-03-30 5:41 ` Martin KaFai Lau
2021-03-30 6:40 ` Song Liu
2021-03-30 16:33 ` [PATCH bpf-next 0/2] bpf: Update doc about calling kernel function Alexei Starovoitov
2 siblings, 1 reply; 6+ messages in thread
From: Martin KaFai Lau @ 2021-03-30 5:41 UTC (permalink / raw)
To: bpf; +Cc: Alexei Starovoitov, Daniel Borkmann, kernel-team, netdev
This patch updates the README.rst to specify the clang requirement
to compile the bpf selftests that call kernel function.
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
---
tools/testing/selftests/bpf/README.rst | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst
index 3464161c8eea..65fe318d1e71 100644
--- a/tools/testing/selftests/bpf/README.rst
+++ b/tools/testing/selftests/bpf/README.rst
@@ -179,3 +179,17 @@ types, which was introduced in `Clang 13`__. The older Clang versions will
either crash when compiling these tests, or generate an incorrect BTF.
__ https://reviews.llvm.org/D83289
+
+Kernel function call test and Clang version
+===========================================
+
+Some selftests (e.g. kfunc_call and bpf_tcp_ca) require a LLVM support
+to generate extern function in BTF. It was introduced in `Clang 13`__.
+
+Without it, the error from compiling bpf selftests looks like:
+
+.. code-block:: console
+
+ libbpf: failed to find BTF for extern 'tcp_slow_start' [25] section: -2
+
+__ https://reviews.llvm.org/D93563
--
2.30.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH bpf-next 0/2] bpf: Update doc about calling kernel function
2021-03-30 5:41 [PATCH bpf-next 0/2] bpf: Update doc about calling kernel function Martin KaFai Lau
2021-03-30 5:41 ` [PATCH bpf-next 1/2] bpf: Update bpf_design_QA.rst to clarify the kfunc call is not ABI Martin KaFai Lau
2021-03-30 5:41 ` [PATCH bpf-next 2/2] bpf: selftests: Update clang requirement in README.rst for testing kfunc call Martin KaFai Lau
@ 2021-03-30 16:33 ` Alexei Starovoitov
2 siblings, 0 replies; 6+ messages in thread
From: Alexei Starovoitov @ 2021-03-30 16:33 UTC (permalink / raw)
To: Martin KaFai Lau
Cc: bpf, Alexei Starovoitov, Daniel Borkmann, Kernel Team,
Network Development
On Mon, Mar 29, 2021 at 10:41 PM Martin KaFai Lau <kafai@fb.com> wrote:
>
> This set updates the document about the bpf program calling kernel
> function. In particular, updates are regarding to the clang
> requirement in selftests and kfunc-call not an ABI.
Applied.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-03-30 16:34 UTC | newest]
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2021-03-30 5:41 [PATCH bpf-next 0/2] bpf: Update doc about calling kernel function Martin KaFai Lau
2021-03-30 5:41 ` [PATCH bpf-next 1/2] bpf: Update bpf_design_QA.rst to clarify the kfunc call is not ABI Martin KaFai Lau
2021-03-30 6:40 ` Song Liu
2021-03-30 5:41 ` [PATCH bpf-next 2/2] bpf: selftests: Update clang requirement in README.rst for testing kfunc call Martin KaFai Lau
2021-03-30 6:40 ` Song Liu
2021-03-30 16:33 ` [PATCH bpf-next 0/2] bpf: Update doc about calling kernel function Alexei Starovoitov
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