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overlay_linux.go
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overlay_linux.go
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package driver
import (
"bytes"
"fmt"
"os"
"os/exec"
"path/filepath"
"strings"
"syscall"
)
type OverlayDriver struct {
OverlaysDir string
}
func (driver *OverlayDriver) CreateVolume(path string) error {
layerDir := driver.layerDir(path)
err := os.MkdirAll(layerDir, 0755)
if err != nil {
return err
}
err = os.Mkdir(path, 0755)
if err != nil {
return err
}
return syscall.Mount(layerDir, path, "", syscall.MS_BIND, "")
}
func (driver *OverlayDriver) DestroyVolume(path string) error {
err := syscall.Unmount(path, 0)
if err != nil {
return err
}
err = os.RemoveAll(driver.workDir(path))
if err != nil {
return err
}
err = os.RemoveAll(driver.layerDir(path))
if err != nil {
return err
}
return os.RemoveAll(path)
}
func (driver *OverlayDriver) CreateCopyOnWriteLayer(path string, parent string) error {
ancestry, err := driver.ancestry(parent)
if err != nil {
return err
}
childDir := driver.layerDir(path)
workDir := driver.workDir(path)
err = os.MkdirAll(childDir, 0755)
if err != nil {
return err
}
err = os.MkdirAll(workDir, 0755)
if err != nil {
return err
}
err = os.MkdirAll(path, 0755)
if err != nil {
return err
}
opts := fmt.Sprintf(
"lowerdir=%s,upperdir=%s,workdir=%s",
strings.Join(ancestry, ":"),
childDir,
workDir,
)
return syscall.Mount("overlay", path, "overlay", 0, opts)
}
func (driver *OverlayDriver) GetVolumeSizeInBytes(path string) (int64, error) {
stdout := &bytes.Buffer{}
cmd := exec.Command("du", "-s", driver.layerDir(path))
cmd.Stdout = stdout
err := cmd.Run()
if err != nil {
return 0, err
}
var size int64
_, err = fmt.Sscanf(stdout.String(), "%d", &size)
if err != nil {
return 0, err
}
return size, nil
}
func (driver *OverlayDriver) layerDir(path string) string {
return filepath.Join(driver.OverlaysDir, driver.pathId(path))
}
func (driver *OverlayDriver) workDir(path string) string {
return filepath.Join(driver.OverlaysDir, "work", driver.pathId(path))
}
func (driver *OverlayDriver) ancestry(path string) ([]string, error) {
ancestry := []string{}
currentPath := path
for {
ancestry = append(ancestry, driver.layerDir(currentPath))
parentVolume, err := os.Readlink(filepath.Join(filepath.Dir(currentPath), "parent"))
if err != nil {
if _, ok := err.(*os.PathError); ok {
break
}
return nil, err
}
currentPath = filepath.Join(parentVolume, "volume")
}
return ancestry, nil
}
func (driver *OverlayDriver) pathId(path string) string {
return filepath.Base(filepath.Dir(path))
}