netdev - [PATCH bpf 2/2] bpf: Update bpf_design_QA.rst to clarify that attaching to functions is not ABI

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Message-Id: <20220722180641.2902585-2-paulmck@kernel.org>
Date:   Fri, 22 Jul 2022 11:06:41 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-doc@...r.kernel.org
Cc:     corbet@....net, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, kernel-team@...com,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH bpf 2/2] bpf: Update bpf_design_QA.rst to clarify that attaching to functions is not ABI

This patch updates bpf_design_QA.rst to clarify that the ability to
attach a BPF program to a given function in the kernel does not make
that function become part of the Linux kernel's ABI.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 Documentation/bpf/bpf_design_QA.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Documentation/bpf/bpf_design_QA.rst b/Documentation/bpf/bpf_design_QA.rst
index 2ed9128cfbec8..46337a60255e9 100644
--- a/Documentation/bpf/bpf_design_QA.rst
+++ b/Documentation/bpf/bpf_design_QA.rst
@@ -279,3 +279,15 @@ 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.
+
+Q: Attaching to kernel functions is an ABI?
+-------------------------------------------
+Q: BPF programs can be attached to many kernel functions.  Do these
+kernel functions become part of the ABI?
+
+A: NO.
+
+The kernel function prototypes will change, and BPF programs attaching to
+them will need to change.  The BPF compile-once-run-everywhere (CO-RE)
+should be used in order to make it easier to adapt your BPF programs to
+different versions of the kernel.
-- 
2.31.1.189.g2e36527f23