vendor/github.com/Microsoft/hcsshim/internal/wclayer/layerutils.go

//go:build windows

package wclayer

// This file contains utility functions to support storage (graph) related
// functionality.

import (
	"context"
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"syscall"

	"github.com/Microsoft/go-winio/pkg/guid"
	"github.com/sirupsen/logrus"
)

/*
To pass into syscall, we need a struct matching the following:

enum GraphDriverType
{
    DiffDriver,
    FilterDriver
};

struct DriverInfo {
    GraphDriverType Flavour;
    LPCWSTR HomeDir;
};
*/

type driverInfo struct {
	Flavour  int
	HomeDirp *uint16
}

var (
	utf16EmptyString uint16
	stdDriverInfo    = driverInfo{1, &utf16EmptyString}
)

/*
To pass into syscall, we need a struct matching the following:

typedef struct _WC_LAYER_DESCRIPTOR {

	//
	// The ID of the layer
	//

	GUID LayerId;

	//
	// Additional flags
	//

	union {
	    struct {
	        ULONG Reserved : 31;
	        ULONG Dirty : 1;    // Created from sandbox as a result of snapshot
	    };
	    ULONG Value;
	} Flags;

	//
	// Path to the layer root directory, null-terminated
	//

	PCWSTR Path;

} WC_LAYER_DESCRIPTOR, *PWC_LAYER_DESCRIPTOR;
*/
type WC_LAYER_DESCRIPTOR struct {
	LayerId guid.GUID
	Flags   uint32
	Pathp   *uint16
}

func layerPathsToDescriptors(ctx context.Context, parentLayerPaths []string) ([]WC_LAYER_DESCRIPTOR, error) {
	// Array of descriptors that gets constructed.
	var layers []WC_LAYER_DESCRIPTOR

	for i := 0; i < len(parentLayerPaths); i++ {
		g, err := LayerID(ctx, parentLayerPaths[i])
		if err != nil {
			logrus.WithError(err).Debug("Failed to convert name to guid")
			return nil, err
		}

		p, err := syscall.UTF16PtrFromString(parentLayerPaths[i])
		if err != nil {
			logrus.WithError(err).Debug("Failed conversion of parentLayerPath to pointer")
			return nil, err
		}

		layers = append(layers, WC_LAYER_DESCRIPTOR{
			LayerId: g,
			Flags:   0,
			Pathp:   p,
		})
	}

	return layers, nil
}

// GetLayerUvmBuild looks for a file named `uvmbuildversion` at `layerPath\uvmbuildversion` and returns the
// build number of the UVM from that file.
func GetLayerUvmBuild(layerPath string) (uint16, error) {
	data, err := os.ReadFile(filepath.Join(layerPath, UvmBuildFileName))
	if err != nil {
		return 0, err
	}
	ver, err := strconv.ParseUint(string(data), 10, 16)
	if err != nil {
		return 0, err
	}
	return uint16(ver), nil
}

// WriteLayerUvmBuildFile writes a file at path `layerPath\uvmbuildversion` that contains the given `build`
// version for future reference.
func WriteLayerUvmBuildFile(layerPath string, build uint16) error {
	return os.WriteFile(filepath.Join(layerPath, UvmBuildFileName), []byte(fmt.Sprintf("%d", build)), 0777)
}