docs/graphdriver/driver.go

package graphdriver

import (
	"fmt"
	"github.com/dotcloud/docker/archive"
	"github.com/dotcloud/docker/utils"
	"os"
	"path"
	"strings"
	"syscall"
)

type InitFunc func(root string) (Driver, error)

type Driver interface {
	String() string

	Create(id, parent string) error
	Remove(id string) error

	Get(id string) (dir string, err error)
	Exists(id string) bool

	Status() [][2]string

	Cleanup() error
}

type Differ interface {
	Diff(id string) (archive.Archive, error)
	Changes(id string) ([]archive.Change, error)
	ApplyDiff(id string, diff archive.Archive) error
	DiffSize(id string) (bytes int64, err error)
}

type Mount struct {
	Device  string
	Target  string
	Type    string
	Options string
}

var (
	DefaultDriver string
	// All registred drivers
	drivers map[string]InitFunc
	// Slice of drivers that should be used in an order
	priority = []string{
		"aufs",
		"devicemapper",
		"vfs",
	}
)

func init() {
	drivers = make(map[string]InitFunc)
}

func Register(name string, initFunc InitFunc) error {
	if _, exists := drivers[name]; exists {
		return fmt.Errorf("Name already registered %s", name)
	}
	drivers[name] = initFunc

	return nil
}

func GetDriver(name, home string) (Driver, error) {
	if initFunc, exists := drivers[name]; exists {
		return initFunc(path.Join(home, name))
	}
	return nil, fmt.Errorf("No such driver: %s", name)
}

func New(root string) (driver Driver, err error) {
	for _, name := range []string{os.Getenv("DOCKER_DRIVER"), DefaultDriver} {
		if name != "" {
			return GetDriver(name, root)
		}
	}

	// Check for priority drivers first
	for _, name := range priority {
		if driver, err = GetDriver(name, root); err != nil {
			utils.Debugf("Error loading driver %s: %s", name, err)
			continue
		}
		return driver, nil
	}

	// Check all registered drivers if no priority driver is found
	for _, initFunc := range drivers {
		if driver, err = initFunc(root); err != nil {
			continue
		}
		return driver, nil
	}
	return nil, err
}

func (m *Mount) Mount(root string) error {
	var (
		flag   int
		data   []string
		target = path.Join(root, m.Target)
	)

	if mounted, err := Mounted(target); err != nil || mounted {
		return err
	}

	flags := map[string]struct {
		clear bool
		flag  int
	}{
		"defaults":      {false, 0},
		"ro":            {false, syscall.MS_RDONLY},
		"rw":            {true, syscall.MS_RDONLY},
		"suid":          {true, syscall.MS_NOSUID},
		"nosuid":        {false, syscall.MS_NOSUID},
		"dev":           {true, syscall.MS_NODEV},
		"nodev":         {false, syscall.MS_NODEV},
		"exec":          {true, syscall.MS_NOEXEC},
		"noexec":        {false, syscall.MS_NOEXEC},
		"sync":          {false, syscall.MS_SYNCHRONOUS},
		"async":         {true, syscall.MS_SYNCHRONOUS},
		"dirsync":       {false, syscall.MS_DIRSYNC},
		"remount":       {false, syscall.MS_REMOUNT},
		"mand":          {false, syscall.MS_MANDLOCK},
		"nomand":        {true, syscall.MS_MANDLOCK},
		"atime":         {true, syscall.MS_NOATIME},
		"noatime":       {false, syscall.MS_NOATIME},
		"diratime":      {true, syscall.MS_NODIRATIME},
		"nodiratime":    {false, syscall.MS_NODIRATIME},
		"bind":          {false, syscall.MS_BIND},
		"rbind":         {false, syscall.MS_BIND | syscall.MS_REC},
		"relatime":      {false, syscall.MS_RELATIME},
		"norelatime":    {true, syscall.MS_RELATIME},
		"strictatime":   {false, syscall.MS_STRICTATIME},
		"nostrictatime": {true, syscall.MS_STRICTATIME},
	}

	for _, o := range strings.Split(m.Options, ",") {
		// If the option does not exist in the flags table then it is a
		// data value for a specific fs type
		if f, exists := flags[o]; exists {
			if f.clear {
				flag &= ^f.flag
			} else {
				flag |= f.flag
			}
		} else {
			data = append(data, o)
		}
	}

	if err := syscall.Mount(m.Device, target, m.Type, uintptr(flag), strings.Join(data, ",")); err != nil {
		panic(err)
	}
	return nil
}

func (m *Mount) Unmount(root string) error {
	target := path.Join(root, m.Target)
	if mounted, err := Mounted(target); err != nil || !mounted {
		return err
	}
	return syscall.Unmount(target, 0)
}

func Mounted(mountpoint string) (bool, error) {
	mntpoint, err := os.Stat(mountpoint)
	if err != nil {
		if os.IsNotExist(err) {
			return false, nil
		}
		return false, err
	}
	parent, err := os.Stat(path.Join(mountpoint, ".."))
	if err != nil {
		return false, err
	}
	mntpointSt := mntpoint.Sys().(*syscall.Stat_t)
	parentSt := parent.Sys().(*syscall.Stat_t)

	return mntpointSt.Dev != parentSt.Dev, nil
}