native Send implementation

btrfs.go

@@ -6,17 +6,26 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"syscall"
 )
 
 const SuperMagic = 0x9123683E
 
-func Open(path string) (*FS, error) {
+func Open(path string, ro bool) (*FS, error) {
 	if ok, err := IsSubVolume(path); err != nil {
 		return nil, err
 	} else if !ok {
 		return nil, ErrNotBtrfs{Path: path}
 	}
-	dir, err := os.Open(path)
+	var (
+		dir *os.File
+		err error
+	)
+	if ro {
+		dir, err = os.OpenFile(path, os.O_RDONLY|syscall.O_NOATIME, 0644)
+	} else {
+		dir, err = os.Open(path)
+	}
 	if err != nil {
 		return nil, err
 	} else if st, err := dir.Stat(); err != nil {
@@ -139,6 +148,10 @@ func (f *FS) GetSupportedFeatures() (out FSFeatureFlags, err error) {
 	return
 }
 
+func (f *FS) GetFlags() (SubvolFlags, error) {
+	return iocSubvolGetflags(f.f)
+}
+
 func (f *FS) Sync() (err error) {
 	if err = ioctl.Do(f.f, _BTRFS_IOC_START_SYNC, nil); err != nil {
 		return

cmd/gbtrfs.go

@@ -19,6 +19,8 @@ func init() {
 		SubvolumeDeleteCmd,
 		SubvolumeListCmd,
 	)
+
+	SendCmd.Flags().StringP("parent", "p", "", "Send an incremental stream from <parent> to <subvol>.")
 }
 
 var RootCmd = &cobra.Command{
@@ -27,7 +29,8 @@ var RootCmd = &cobra.Command{
 }
 
 var SubvolumeCmd = &cobra.Command{
-	Use: "subvolume <command> <args>",
+	Use:     "subvolume <command> <args>",
+	Aliases: []string{"subvol", "sub", "sv"},
 }
 
 var SubvolumeCreateCmd = &cobra.Command{
@@ -64,8 +67,9 @@ operation is safely stored on the media.`,
 }
 
 var SubvolumeListCmd = &cobra.Command{
-	Use:   "list <mount>",
-	Short: "List subvolumes",
+	Use:     "list <mount>",
+	Short:   "List subvolumes",
+	Aliases: []string{"ls"},
 	RunE: func(cmd *cobra.Command, args []string) error {
 		if len(args) != 1 {
 			return fmt.Errorf("expected one destination argument")
@@ -81,12 +85,13 @@ var SubvolumeListCmd = &cobra.Command{
 }
 
 var SendCmd = &cobra.Command{
-	Use:   "send [-ve] [-p <parent>] [-c <clone-src>] [-f <outfile>] <subvol> [<subvol>...]",
+	Use:   "send [-v] [-p <parent>] [-c <clone-src>] [-f <outfile>] <subvol> [<subvol>...]",
 	Short: "Send the subvolume(s) to stdout.",
 	Long: `Sends the subvolume(s) specified by <subvol> to stdout.
 <subvol> should be read-only here.`,
 	RunE: func(cmd *cobra.Command, args []string) error {
-		return btrfs.Send(os.Stdout, "", args...)
+		parent, _ := cmd.Flags().GetString("parent")
+		return btrfs.Send(os.Stdout, parent, args...)
 	},
 }
 

ioctl_h.go

@@ -5,6 +5,8 @@ import (
 	"encoding/hex"
 	"github.com/dennwc/btrfs/ioctl"
 	"os"
+	"strconv"
+	"strings"
 	"unsafe"
 )
 
@@ -86,7 +88,25 @@ type btrfs_ioctl_vol_args_v2_u1 struct {
 
 const subvolNameMax = 4039
 
-type subvolFlags uint64
+type SubvolFlags uint64
+
+func (f SubvolFlags) ReadOnly() bool {
+	return f&SubvolReadOnly != 0
+}
+func (f SubvolFlags) String() string {
+	if f == 0 {
+		return "<nil>"
+	}
+	var out []string
+	if f&SubvolReadOnly != 0 {
+		out = append(out, "RO")
+		f = f & (^SubvolReadOnly)
+	}
+	if f != 0 {
+		out = append(out, "0x"+strconv.FormatInt(int64(f), 16))
+	}
+	return strings.Join(out, "|")
+}
 
 // flags for subvolumes
 //
@@ -97,15 +117,15 @@ type subvolFlags uint64
 // - BTRFS_IOC_SUBVOL_GETFLAGS
 // - BTRFS_IOC_SUBVOL_SETFLAGS
 const (
-	subvolCreateAsync   = subvolFlags(1 << 0)
-	subvolReadOnly      = subvolFlags(1 << 1)
-	subvolQGroupInherit = subvolFlags(1 << 2)
+	subvolCreateAsync   = SubvolFlags(1 << 0)
+	SubvolReadOnly      = SubvolFlags(1 << 1)
+	subvolQGroupInherit = SubvolFlags(1 << 2)
 )
 
 type btrfs_ioctl_vol_args_v2 struct {
 	fd      int64
 	transid uint64
-	flags   subvolFlags
+	flags   SubvolFlags
 	btrfs_ioctl_vol_args_v2_u1
 	unused [2]uint64
 	name   [subvolNameMax + 1]byte
@@ -670,8 +690,9 @@ func iocWaitSync(f *os.File, out *uint64) error {
 	return ioctl.Do(f, _BTRFS_IOC_WAIT_SYNC, out)
 }
 
-func iocSubvolGetflags(f *os.File, out *uint64) error {
-	return ioctl.Do(f, _BTRFS_IOC_SUBVOL_GETFLAGS, out)
+func iocSubvolGetflags(f *os.File) (out SubvolFlags, err error) {
+	err = ioctl.Do(f, _BTRFS_IOC_SUBVOL_GETFLAGS, &out)
+	return
 }
 
 func iocSubvolSetflags(f *os.File, out *uint64) error {
@@ -714,8 +735,8 @@ func iocSetReceivedSubvol(f *os.File, out *btrfs_ioctl_received_subvol_args) err
 	return ioctl.Do(f, _BTRFS_IOC_SET_RECEIVED_SUBVOL, out)
 }
 
-func iocSend(f *os.File, out *btrfs_ioctl_send_args) error {
-	return ioctl.Do(f, _BTRFS_IOC_SEND, out)
+func iocSend(f *os.File, in *btrfs_ioctl_send_args) error {
+	return ioctl.Do(f, _BTRFS_IOC_SEND, in)
 }
 
 func iocDevicesReady(f *os.File, out *btrfs_ioctl_vol_args) error {

send.go

@@ -1,46 +1,124 @@
 package btrfs
 
 import (
-	"bytes"
-	"errors"
+	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
-	"os/exec"
+	"path/filepath"
 )
 
 func Send(w io.Writer, parent string, subvols ...string) error {
 	if len(subvols) == 0 {
 		return nil
 	}
-	// TODO: write a native implementation?
-	args := []string{
-		"send",
-	}
-	if parent != "" {
-		args = append(args, "-p", parent)
-	}
-	tf, err := ioutil.TempFile("", "btrfs_snap")
+	// use first send subvol to determine mount_root
+	subvol, err := filepath.Abs(subvols[0])
 	if err != nil {
 		return err
 	}
-	defer func() {
-		name := tf.Name()
-		tf.Close()
-		os.Remove(name)
-	}()
-	args = append(args, "-f", tf.Name())
-	buf := bytes.NewBuffer(nil)
-	args = append(args, subvols...)
-	cmd := exec.Command("btrfs", args...)
-	cmd.Stderr = buf
-	if err = cmd.Run(); err != nil {
-		if buf.Len() != 0 {
-			return errors.New(buf.String())
-		}
+	mountRoot, err := findMountRoot(subvol)
+	if err == os.ErrNotExist {
+		return fmt.Errorf("cannot find a mountpoint for %s", subvol)
+	} else if err != nil {
 		return err
 	}
-	tf.Seek(0, 0)
-	_, err = io.Copy(w, tf)
-	return err
+	var (
+		cloneSrc []uint64
+		parentID uint64
+	)
+	if parent != "" {
+		parent, err = filepath.Abs(parent)
+		if err != nil {
+			return err
+		}
+		f, err := os.Open(parent)
+		if err != nil {
+			return fmt.Errorf("cannot open parent: %v", err)
+		}
+		id, err := getPathRootID(f)
+		f.Close()
+		if err != nil {
+			return fmt.Errorf("cannot get parent root id: %v", err)
+		}
+		parentID = id
+		cloneSrc = append(cloneSrc, id)
+	}
+	// check all subvolumes
+	paths := make([]string, 0, len(subvols))
+	for _, sub := range subvols {
+		sub, err = filepath.Abs(sub)
+		if err != nil {
+			return err
+		}
+		paths = append(paths, sub)
+		mount, err := findMountRoot(sub)
+		if err != nil {
+			return err
+		} else if mount != mountRoot {
+			return fmt.Errorf("all subvolumes must be from the same filesystem (%s is not)", sub)
+		}
+		ok, err := IsReadOnly(sub)
+		if err != nil {
+			return err
+		} else if !ok {
+			return fmt.Errorf("subvolume %s is not read-only", sub)
+		}
+	}
+	//full := len(cloneSrc) == 0
+	for i, sub := range paths {
+		//if len(cloneSrc) > 1 {
+		//	// TODO: find_good_parent
+		//}
+		//if !full { // TODO
+		//	cloneSrc = append(cloneSrc, )
+		//}
+		fs, err := Open(sub, true)
+		if err != nil {
+			return err
+		}
+		var flags uint64
+		if i != 0 { // not first
+			flags |= _BTRFS_SEND_FLAG_OMIT_STREAM_HEADER
+		}
+		if i < len(paths)-1 { // not last
+			flags |= _BTRFS_SEND_FLAG_OMIT_END_CMD
+		}
+		err = send(w, fs.f, parentID, cloneSrc, flags)
+		if err != nil {
+			return fmt.Errorf("error sending %s: %v", sub, err)
+		}
+	}
+	return nil
+}
+
+func send(w io.Writer, subvol *os.File, parent uint64, sources []uint64, flags uint64) error {
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return err
+	}
+	errc := make(chan error, 1)
+	go func() {
+		defer pr.Close()
+		_, err := io.Copy(w, pr)
+		errc <- err
+	}()
+	fd := pw.Fd()
+	wait := func() error {
+		pw.Close()
+		return <-errc
+	}
+	args := &btrfs_ioctl_send_args{
+		send_fd:     int64(fd),
+		parent_root: parent,
+		flags:       flags,
+	}
+	if len(sources) != 0 {
+		args.clone_sources = &sources[0]
+		args.clone_sources_count = uint64(len(sources))
+	}
+	if err := iocSend(subvol, args); err != nil {
+		wait()
+		return err
+	}
+	return wait()
 }

subvolume.go

@@ -131,7 +131,7 @@ func SnapshotSubVolume(subvol, dst string, ro bool) error {
 		fd: int64(f.Fd()),
 	}
 	if ro {
-		args.flags |= subvolReadOnly
+		args.flags |= SubvolReadOnly
 	}
 	// TODO
 	//if inherit != nil {

utils.go

@@ -1,8 +1,12 @@
 package btrfs
 
 import (
+	"bufio"
 	"fmt"
+	"io"
 	"os"
+	"path/filepath"
+	"strings"
 	"syscall"
 	"unsafe"
 )
@@ -15,6 +19,76 @@ func isBtrfs(path string) (bool, error) {
 	return stfs.Type == SuperMagic, nil
 }
 
+func IsReadOnly(path string) (bool, error) {
+	fs, err := Open(path, true)
+	if err != nil {
+		return false, err
+	}
+	defer fs.Close()
+	f, err := fs.GetFlags()
+	if err != nil {
+		return false, err
+	}
+	return f.ReadOnly(), nil
+}
+
+type mountPoint struct {
+	Dev   string
+	Mount string
+	Type  string
+	Opts  string
+}
+
+func getMounts() ([]mountPoint, error) {
+	file, err := os.Open("/etc/mtab")
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+	r := bufio.NewReader(file)
+	var out []mountPoint
+	for {
+		line, err := r.ReadString('\n')
+		if err == io.EOF {
+			break
+		} else if err != nil {
+			return nil, err
+		}
+		fields := strings.Fields(line)
+		out = append(out, mountPoint{
+			Dev:   fields[0],
+			Mount: fields[1],
+			Type:  fields[2],
+			Opts:  fields[3],
+		})
+	}
+	return out, nil
+}
+
+func findMountRoot(path string) (string, error) {
+	mounts, err := getMounts()
+	if err != nil {
+		return "", err
+	}
+	longest := ""
+	isBtrfs := false
+	for _, m := range mounts {
+		if !strings.HasPrefix(path, m.Mount) {
+			continue
+		}
+		if len(longest) < len(m.Mount) {
+			longest = m.Mount
+			isBtrfs = m.Type == "btrfs"
+		}
+	}
+	if longest == "" {
+		return "", os.ErrNotExist
+	} else if !isBtrfs {
+		return "", ErrNotBtrfs{Path: longest}
+	}
+	return filepath.Abs(longest)
+}
+
 // openDir does the following checks before calling Open:
 // 1: path is in a btrfs filesystem
 // 2: path is a directory