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Add support to test update library with local kernel #1306

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Add support to test update library with local kernel #1306

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10 changes: 10 additions & 0 deletions docs/ebpf/contributing/index.md
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Expand Up @@ -67,6 +67,16 @@ from upstream kernel versions. You can update them to the latest version by:

Finally, bump the tested kernels in `.github/workflows/ci.yml`

Note it's possible to set `KERNEL_VERSION` to location of kernel build artifacts
and update the kernel dependencies to your local kernel build, like:

```shell-session
$ ls ../data/
bpf_testmod.ko libbpf.c vmlinux

$ make update-kernel-deps KERNEL_VERSION=../data
```

## Project permissions

If you'd like to contribute to the library more regularly, one of the
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25 changes: 18 additions & 7 deletions testdata/sh/update-kernel-deps.sh
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Expand Up @@ -12,14 +12,25 @@ cleanup() {

trap cleanup EXIT

# Download and process libbpf.c
curl -fL "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/plain/tools/lib/bpf/libbpf.c?h=v$KERNEL_VERSION" -o "$tmp/libbpf.c"
if [ -d $KERNEL_VERSION ]; then
# Copy libbpf/vmlinux/bpf_testmod from local directory
cp $KERNEL_VERSION/libbpf.c $tmp
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Would it make sense to assume that KERNEL_VERSION is a checkout of the linux source? Then you can just run make KERNEL_VERSION=/path/to/linux. Right now you need to copy things around.

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I guess it's possible, but at the moment I have the kernel build on another server, so current change fits me better.. maybe we could introduce more variables to allow that? I felt like the current change is abusing bit the KERNEL_VERSION variable, but it's simple ;-)

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Hm, maybe you can abuse rsync to get transparent copy from your build server? Basically, the usual thing would be to rsync from a local directory, but if you set your variable to user@host:/path/to/linux it'd slurp that over.

I don't much see the point of adding the option in a way that means extra work for the common case to be honest.

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hum, not sure I see enough benefit in doing the rsync.. I don't think the local kernel update will happen that often.. but I'm ok to keep that change around just for my purposes, there's no need for that to be merged if it's a problem

cp $KERNEL_VERSION/vmlinux $tmp
mkdir -p $tmp/lib/modules
cp $KERNEL_VERSION/bpf_testmod.ko $tmp/lib/modules
else
# Download libbpf.c
curl -fL "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/plain/tools/lib/bpf/libbpf.c?h=v$KERNEL_VERSION" -o "$tmp/libbpf.c"

# Download vmlinux and btf_testmod
extract_oci_image "ghcr.io/cilium/ci-kernels:$KERNEL_VERSION" "$tmp"

"/lib/modules/$(uname -r)/build/scripts/extract-vmlinux" "$tmp/boot/vmlinuz" > "$tmp/vmlinux"
fi

# Process libbpf.c
"./internal/cmd/gensections.awk" "$tmp/libbpf.c" | gofmt > "./elf_sections.go"

# Download and process vmlinux and btf_testmod
extract_oci_image "ghcr.io/cilium/ci-kernels:$KERNEL_VERSION" "$tmp"

"/lib/modules/$(uname -r)/build/scripts/extract-vmlinux" "$tmp/boot/vmlinuz" > "$tmp/vmlinux"

# Process vmlinux and btf_testmod
objcopy --dump-section .BTF=/dev/stdout "$tmp/vmlinux" /dev/null | gzip > "btf/testdata/vmlinux.btf.gz"
find "$tmp/lib/modules" -type f -name bpf_testmod.ko -exec objcopy --dump-section .BTF="btf/testdata/btf_testmod.btf" {} /dev/null \;
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