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improve error handling for einval with lpm trie. #1720

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improve error handling for einval with lpm trie. #1720

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7 changes: 6 additions & 1 deletion map.go
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Original file line number Diff line number Diff line change
Expand Up @@ -556,7 +556,12 @@ func handleMapCreateError(attr sys.MapCreateAttr, spec *MapSpec, err error) erro
if errors.Is(err, unix.EINVAL) && spec.Type == UnspecifiedMap {
return fmt.Errorf("map create: cannot use type %s", UnspecifiedMap)
}
if errors.Is(err, unix.EINVAL) && spec.Flags&sys.BPF_F_NO_PREALLOC > 0 {
// LPM trie key size must be a multiple of 8 and not exceed 2048.
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This seems incorrect according to my experience and the doc https://docs.ebpf.io/linux/map-type/BPF_MAP_TYPE_LPM_TRIE/.

// Ref: https://docs.kernel.org/bpf/map_lpm_trie.html#bpf-map-type-lpm-trie
if errors.Is(err, unix.EINVAL) && spec.Type == LPMTrie && (spec.KeySize%8 != 0 || spec.KeySize > 2048) {
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This is becoming a bit too specific for me. The goal is not to be exhaustive, and the wording here has always been soft on purpose. Could you drop this change?

The actual problem is a false-positive on the error message. I suggest adding the the following to types.go:

func (mt MapType) mustHaveNoPrealloc() bool { }

I'd check the kernel sources for all currently-known cases and make this function return true for LPM, cgroup storage and others that require NO_PREALLOC to be set.

return fmt.Errorf("map create: LPMTrie: invalid key size %d (LPM trie key size must be a multiple of 8 and not exceed 2048)", LPMTrie)
}
if errors.Is(err, unix.EINVAL) && spec.Flags&sys.BPF_F_NO_PREALLOC > 0 && spec.Type != LPMTrie {
return fmt.Errorf("map create: %w (noPrealloc flag may be incompatible with map type %s)", err, spec.Type)
}

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