diff mbox series

[bpf-next,1/2] bpf: Update bpf_design_QA.rst to clarify the kfunc call is not ABI

Message ID 20210330054150.2933542-1-kafai@fb.com
State New
Headers show
Series [bpf-next,1/2] bpf: Update bpf_design_QA.rst to clarify the kfunc call is not ABI | expand

Commit Message

Martin KaFai Lau March 30, 2021, 5:41 a.m. UTC 
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 mbox series

Patch

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.