feat(btrfs_snapshot_hook): reimplemented Btrfs snapshots

TODO: test coverage

worker/btrfs_snapshot_hook.go

@@ -0,0 +1,90 @@
+package worker
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/dennwc/btrfs"
+)
+
+type btrfsSnapshotHook struct {
+	provider           mirrorProvider
+	mirrorSnapshotPath string
+}
+
+// the user who runs the jobs (typically `tunasync`) should be granted the permission to run btrfs commands
+// TODO: check if the filesystem is Btrfs
+func newBtrfsSnapshotHook(provider mirrorProvider, snapshotPath string, mirror mirrorConfig) *btrfsSnapshotHook {
+	mirrorSnapshotPath := mirror.SnapshotPath
+	if mirrorSnapshotPath == "" {
+		mirrorSnapshotPath = filepath.Join(snapshotPath, provider.Name())
+	}
+	return &btrfsSnapshotHook{
+		provider:           provider,
+		mirrorSnapshotPath: mirrorSnapshotPath,
+	}
+}
+
+// check if path `snapshotPath/providerName` exists
+// Case 1: Not exists => create a new subvolume
+// Case 2: Exists as a subvolume => nothing to do
+// Case 3: Exists as a directory => error detected
+func (h *btrfsSnapshotHook) preJob() error {
+	path := h.provider.WorkingDir()
+	if _, err := os.Stat(path); os.IsNotExist(err) {
+		// create subvolume
+		err := btrfs.CreateSubVolume(path)
+		if err != nil {
+			logger.Errorf("failed to create Btrfs subvolume %s: %s", path, err.Error())
+			return err
+		}
+		logger.Noticef("created new Btrfs subvolume %s", path)
+	} else {
+		if is, err := btrfs.IsSubVolume(path); err != nil {
+			return err
+		} else if !is {
+			return fmt.Errorf("path %s exists but isn't a Btrfs subvolume", path)
+		}
+	}
+	return nil
+}
+
+func (h *btrfsSnapshotHook) preExec() error {
+	return nil
+}
+
+func (h *btrfsSnapshotHook) postExec() error {
+	return nil
+}
+
+// delete old snapshot if exists, then create a new snapshot
+func (h *btrfsSnapshotHook) postSuccess() error {
+	if _, err := os.Stat(h.mirrorSnapshotPath); !os.IsNotExist(err) {
+		isSubVol, err := btrfs.IsSubVolume(h.mirrorSnapshotPath)
+		if err != nil {
+			return err
+		} else if !isSubVol {
+			return fmt.Errorf("path %s exists and isn't a Btrfs snapshot", h.mirrorSnapshotPath)
+		}
+		// is old snapshot => delete it
+		if err := btrfs.DeleteSubVolume(h.mirrorSnapshotPath); err != nil {
+			logger.Errorf("failed to delete old Btrfs snapshot %s", h.mirrorSnapshotPath)
+			return err
+		}
+		logger.Noticef("deleted old snapshot %s", h.mirrorSnapshotPath)
+	}
+	// create a new writable snapshot
+	// (the snapshot is writable so that it can be deleted easily)
+	if err := btrfs.SnapshotSubVolume(h.provider.WorkingDir(), h.mirrorSnapshotPath, false); err != nil {
+		logger.Errorf("failed to create new Btrfs snapshot %s", h.mirrorSnapshotPath)
+		return err
+	}
+	logger.Noticef("created new Btrfs snapshot %s", h.mirrorSnapshotPath)
+	return nil
+}
+
+// keep the old snapshot => nothing to do
+func (h *btrfsSnapshotHook) postFail() error {
+	return nil
+}

worker/config.go

@@ -38,6 +38,7 @@ type Config struct {
 	Server        serverConfig        `toml:"server"`
 	Cgroup        cgroupConfig        `toml:"cgroup"`
 	ZFS           zfsConfig           `toml:"zfs"`
+	BtrfsSnapshot btrfsSnapshotConfig `toml:"btrfs_snapshot"`
 	Docker        dockerConfig        `toml:"docker"`
 	Include       includeConfig       `toml:"include"`
 	Mirrors       []mirrorConfig      `toml:"mirrors"`
@@ -96,6 +97,11 @@ type zfsConfig struct {
 	Zpool  string `toml:"zpool"`
 }
 
+type btrfsSnapshotConfig struct {
+	Enable       bool   `toml:"enable"`
+	SnapshotPath string `toml:"snapshot_path"`
+}
+
 type includeConfig struct {
 	IncludeMirrors string `toml:"include_mirrors"`
 }
@@ -136,6 +142,8 @@ type mirrorConfig struct {
 	DockerImage   string   `toml:"docker_image"`
 	DockerVolumes []string `toml:"docker_volumes"`
 	DockerOptions []string `toml:"docker_options"`
+
+	SnapshotPath string `toml:"snapshot_path"`
 }
 
 // LoadConfig loads configuration

worker/provider.go

@@ -180,6 +180,11 @@ func newMirrorProvider(mirror mirrorConfig, cfg *Config) mirrorProvider {
 		provider.AddHook(newZfsHook(provider, cfg.ZFS.Zpool))
 	}
 
+	// Add Btrfs Snapshot Hook
+	if cfg.BtrfsSnapshot.Enable {
+		provider.AddHook(newBtrfsSnapshotHook(provider, cfg.BtrfsSnapshot.SnapshotPath, mirror))
+	}
+
 	// Add Docker Hook
 	if cfg.Docker.Enable && len(mirror.DockerImage) > 0 {
 		provider.AddHook(newDockerHook(provider, cfg.Docker, mirror))