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bpf, doc: update design qa to reflect kern_version requirement

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Update the bpf_design_QA.rst to also reflect recent changes in
6c4fc209fc ("bpf: remove useless version check for prog load").

Suggested-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2019-01-07 22:57:17 +01:00 • committed by Alexei Starovoitov
parent a8911d6d58
commit a769fa7208
1 changed files with 5 additions and 6 deletions
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11
Documentation/bpf/bpf_design_QA.rst
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@ -157,12 +157,11 @@ Q: Does BPF have a stable ABI?
------------------------------ ------------------------------
A: YES. BPF instructions, arguments to BPF programs, set of helper A: YES. BPF instructions, arguments to BPF programs, set of helper
functions and their arguments, recognized return codes are all part functions and their arguments, recognized return codes are all part
of ABI. However when tracing programs are using bpf_probe_read() helper of ABI. However there is one specific exception to tracing programs
to walk kernel internal datastructures and compile with kernel which are using helpers like bpf_probe_read() to walk kernel internal
internal headers these accesses can and will break with newer data structures and compile with kernel internal headers. Both of these
kernels. The union bpf_attr -> kern_version is checked at load time kernel internals are subject to change and can break with newer kernels
to prevent accidentally loading kprobe-based bpf programs written such that the program needs to be adapted accordingly.
for a different kernel. Networking programs don't do kern_version check.
Q: How much stack space a BPF program uses? Q: How much stack space a BPF program uses?
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