Method fixupMagicFields

map.go:137–187

fixupMagicFields fills fields of MapSpec which are usually left empty in ELF or which depend on runtime information. The method doesn't modify Spec, instead returning a copy. The copy is only performed if fixups are necessary, so callers mustn't mutate the returned spec.

()

// The copy is only performed if fixups are necessary, so callers mustn't mutate
// the returned spec.
func (spec *MapSpec) fixupMagicFields() (*MapSpec, error) {
	switch {
	case spec.Type.canStoreMap():
		if spec.ValueSize != 0 && spec.ValueSize != 4 {
			return nil, errors.New("ValueSize must be zero or four for map of map")
		}

		spec = spec.Copy()
		spec.ValueSize = 4

	case spec.Type == PerfEventArray:
		if spec.KeySize != 0 && spec.KeySize != 4 {
			return nil, errors.New("KeySize must be zero or four for perf event array")
		}

		if spec.ValueSize != 0 && spec.ValueSize != 4 {
			return nil, errors.New("ValueSize must be zero or four for perf event array")
		}

		spec = spec.Copy()
		spec.KeySize = 4
		spec.ValueSize = 4

		n, err := PossibleCPU()
		if err != nil {
			return nil, fmt.Errorf("fixup perf event array: %w", err)
		}

		if n := uint32(n); spec.MaxEntries == 0 || spec.MaxEntries > n {
			// MaxEntries should be zero most of the time, but there is code
			// out there which hardcodes large constants. Clamp the number
			// of entries to the number of CPUs at most. Allow creating maps with
			// less than n items since some kernel selftests relied on this
			// behaviour in the past.
			spec.MaxEntries = n
		}

	case spec.Type == CPUMap:
		n, err := PossibleCPU()
		if err != nil {
			return nil, fmt.Errorf("fixup cpu map: %w", err)
		}

		if n := uint32(n); spec.MaxEntries == 0 || spec.MaxEntries > n {
			// Perform clamping similar to PerfEventArray.
			spec.MaxEntries = n
		}
	}

	return spec, nil
}

// dataSection returns the contents of a datasec if the MapSpec represents one.
func (ms *MapSpec) dataSection() ([]byte, error) {