src/pkg/tools/partutil/gptpriority.go

// Copyright 2026 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package partutil

import (
	"fmt"
	"strconv"
	"strings"
)

func parseGUIDAttrs(field string) (uint64, error) {
	var result uint64
	field = strings.TrimPrefix(field, "GUID:")
	for _, bit := range strings.Split(field, ",") {
		bitNum, err := strconv.Atoi(bit)
		if err != nil {
			return result, err
		}
		result |= 1 << bitNum
	}
	return result, nil
}

// ParseGPTAttrs reads a GPT attributes string output by sfdisk and converts it
// into a uint64 with the appropriate bits set.
func ParseGPTAttrs(attrs string) (uint64, error) {
	var result uint64
	fields := strings.Fields(attrs)
	for i, field := range fields {
		if strings.HasPrefix(field, "GUID:") {
			guidBits, err := parseGUIDAttrs(field)
			if err != nil {
				return result, fmt.Errorf("could not parse field %d: %v", i, err)
			}
			result |= guidBits
		} else if field == "RequiredPartition" {
			result |= 1 << 0
		} else if field == "NoBlockIOProtocol" {
			result |= 1 << 1
		} else if field == "LegacyBIOSBootable" {
			result |= 1 << 2
		} else {
			return result, fmt.Errorf("unknown field %q when parsing %q", field, attrs)
		}
	}
	return result, nil
}

// GPTPriority extracts the GPT priority value from the given sfdisk attributes.
func GPTPriority(attrs string) (uint64, error) {
	bits, err := ParseGPTAttrs(attrs)
	if err != nil {
		return 0, err
	}
	return (bits >> 48) & 0xf, nil
}