src/pkg/dkms/versions.go

package dkms

import (
	"context"
	"fmt"
	"os"
	"os/exec"
	"path"
	"strings"

	"cos.googlesource.com/cos/tools.git/src/pkg/fs"
	"cos.googlesource.com/cos/tools.git/src/pkg/gcs"
	"github.com/golang/glog"
)

// CompareVersions compares two kernel module or package versions and returns
// -1 if the first is less than the second, 0 if they are equal, and 1 if the
// first is greater than the second.
//
// Specifically, it pads each number in the version strings with leading 0s so
// that all numbers have at least 3 digits, then compares them in alphabetical
// order. While this choice of comparison is arbitrary, this is precisely what
// standard DKMS does. Because kernel module version strings do not follow a
// standard format like semver, any choice of comparison is arbitrary, and
// this at least handles common cases well.
//
// This is not compatible with semver version comparison. Specifically,
// the way pre-release versions are compared differs, though the
// major/minor/patch version comparison should be the same in most cases.
func CompareVersions(a, b string) int {
	return strings.Compare(padDigits(a, 3), padDigits(b, 3))
}

// padDigits pads all of the numbers in a string to contain at least
// padNumber digits.
func padDigits(s string, padNumber int) string {
	// Going from right to left, we keep track of how many digits we've
	// seen in the current run of digits. If we see a non-digit before
	// we've seen padNumber digits, we insert enough 0s to increase
	// the number of digits to padNumber. We then reset our digitCount
	// to 0 and continue.
	digitCount := 0
	var reversedChars []byte
	for i := len(s) - 1; i >= 0; i-- {
		c := s[i]
		if c >= '0' && c <= '9' {
			digitCount += 1
		} else {
			for j := digitCount; j < padNumber; j++ {
				reversedChars = append(reversedChars, '0')
			}
			digitCount = 0
		}
		reversedChars = append(reversedChars, c)
	}
	// If the last character we looked at was a digit, it needs to
	// be padded too.
	for j := digitCount; j < padNumber; j++ {
		reversedChars = append(reversedChars, '0')
	}

	var chars []byte
	for i := len(reversedChars) - 1; i >= 0; i-- {
		chars = append(chars, reversedChars[i])
	}

	result := string(chars)
	return result
}

// ModuleVersion returns the version of a compiled module based on the version
// string output by modinfo.
func ModuleVersion(moduleNameOrPath string) (string, error) {
	cmd := exec.Command("modinfo", "-F", "version", moduleNameOrPath)
	out, err := cmd.CombinedOutput()
	if err != nil {
		glog.Error(string(out))
		return "", fmt.Errorf("error running command %v: %v", cmd, err)
	}
	if len(out) == 0 {
		return "", fmt.Errorf("could not find version for %s in modinfo", moduleNameOrPath)
	}

	return strings.TrimSpace(string(out)), nil
}

// CompatiblePackageVersions checks the local DKMS tree for non-broken
// packages which have the same field values as a provided package except for
// the Version, and returns the version of each compatible package.
func CompatiblePackageVersions(pkg *Package) ([]string, error) {
	var versions []string

	packageDir := path.Join(pkg.Trees.Dkms, pkg.Name)
	if !fs.IsDir(packageDir) {
		return versions, nil
	}

	entries, err := os.ReadDir(packageDir)
	if err != nil {
		// If the package directory doesn't exist locally, it just means that the
		// package is not yet built locally, which is not an error.
		if os.IsNotExist(err) {
			return versions, nil
		} else {
			return nil, fmt.Errorf("couldn't read package dkms tree at %s: %v", packageDir, err)
		}
	}

	for _, entry := range entries {
		candidateVersion := entry.Name()

		// Create a copy of package with the candidate version; if that
		// package exists and is not broken, then it is compatible with
		// the current system
		candidatePackage := pkg
		candidatePackage.Version = candidateVersion
		if Status(candidatePackage) != Broken {
			versions = append(versions, candidateVersion)
		}
	}

	return versions, nil
}

// CachedCompatiblePackageVersions checks the DKMS tree in a GCS bucket for
// non-broken packages which have the same field values as a provided package
// except for the Version, and returns the version of each compatible package.
func CachedCompatiblePackageVersions(ctx context.Context, pkg *Package, cache *gcs.GCSBucket) ([]string, error) {
	var versions []string
	packageUri := cache.URI(pkg.Name)

	candidatePaths, err := cache.ListDir(ctx, pkg.Name)
	if err != nil {
		return nil, fmt.Errorf("couldn't read cached package dkms tree at %s: %v", packageUri, err)
	}

	for _, candidatePath := range candidatePaths {
		// Create a copy of package with the candidate version; if that
		// package exists and is not broken, then it is compatible with
		// the current system
		candidatePath = path.Clean(candidatePath) // remove trailing slash
		_, candidateVersion := path.Split(candidatePath)
		candidatePackage := pkg
		candidatePackage.Version = candidateVersion
		if CachedStatus(ctx, candidatePackage, cache) != Broken {
			versions = append(versions, candidateVersion)
		}
	}

	return versions, nil
}