bpf, doc: update design qa to reflect kern_version requirement
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>
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@ -157,12 +157,11 @@ Q: Does BPF have a stable ABI?
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------------------------------
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A: YES. BPF instructions, arguments to BPF programs, set of helper
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functions and their arguments, recognized return codes are all part
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of ABI. However when tracing programs are using bpf_probe_read() helper
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to walk kernel internal datastructures and compile with kernel
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internal headers these accesses can and will break with newer
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kernels. The union bpf_attr -> kern_version is checked at load time
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to prevent accidentally loading kprobe-based bpf programs written
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for a different kernel. Networking programs don't do kern_version check.
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of ABI. However there is one specific exception to tracing programs
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which are using helpers like bpf_probe_read() to walk kernel internal
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data structures and compile with kernel internal headers. Both of these
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kernel internals are subject to change and can break with newer kernels
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such that the program needs to be adapted accordingly.
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Q: How much stack space a BPF program uses?
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-------------------------------------------
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