Merge pull request #18 from dfjxs/layer-cache

Add option to replace symlink layers with cached layers

cmd/commands/env.go

@@ -47,6 +47,7 @@ func explorerEnvironment(clictx *cli.Context) (context.Context, explorers.Contai
 	dockerroot := clictx.GlobalString("docker-root")
 	metadatafile := clictx.GlobalString("metadata-file")
 	snapshotfile := clictx.GlobalString("snapshot-metadata-file")
+	layercache := clictx.GlobalString("layer-cache")
 
 	// Read support container data if provided using global switch.
 	var sc *explorers.SupportContainer
@@ -119,7 +120,10 @@ func explorerEnvironment(clictx *cli.Context) (context.Context, explorers.Contai
 		"snapshotfile":   snapshotfile,
 	}).Debug("containerd container environment")
 
-	cde, err := containerd.NewExplorer(imageroot, containerdroot, metadatafile, snapshotfile, sc)
+	if !clictx.GlobalBool("use-layer-cache") {
+		layercache = ""
+	}
+	cde, err := containerd.NewExplorer(imageroot, containerdroot, metadatafile, snapshotfile, layercache, sc)
 	if err != nil {
 		return ctx, nil, func() { cancel() }, err
 	}

cmd/main.go

@@ -84,6 +84,15 @@ func main() {
 			Name:  "snapshot-metadata-file, s",
 			Usage: "specify the path to containerd snapshot metadata file i.e. metadata.db.",
 		},
+		cli.BoolFlag{
+			Name:  "use-layer-cache",
+			Usage: "attempt to use cached layers where layers are symlinks",
+		},
+		cli.StringFlag{
+			Name:  "layer-cache",
+			Usage: "cached layer folder within the snapshot root",
+			Value: "layers",
+		},
 		cli.StringFlag{
 			Name:  "namespace, n",
 			Usage: "specify container namespace",

explorers/containerd/containerd.go

@@ -38,16 +38,17 @@ import (
 )
 
 type explorer struct {
-	imageroot string                      // mounted image path
-	root      string                      // containerd root
-	manifest  string                      // path to manifest database file i.e. meta.db
-	snapshot  string                      // path to snapshot database file i.e. metadata.db
-	mdb       *bolt.DB                    // manifest database
-	sc        *explorers.SupportContainer // support container structure object
+	imageroot  string                      // mounted image path
+	root       string                      // containerd root
+	manifest   string                      // path to manifest database file i.e. meta.db
+	snapshot   string                      // path to snapshot database file i.e. metadata.db
+	layercache string                      // layer cache folder within snapshot root
+	mdb        *bolt.DB                    // manifest database
+	sc         *explorers.SupportContainer // support container structure object
 }
 
 // NewExplorer returns a ContainerExplorer interface to explore containerd.
-func NewExplorer(imageroot string, root string, manifest string, snapshot string, sc *explorers.SupportContainer) (explorers.ContainerExplorer, error) {
+func NewExplorer(imageroot string, root string, manifest string, snapshot string, layercache string, sc *explorers.SupportContainer) (explorers.ContainerExplorer, error) {
 	opt := &bolt.Options{
 		ReadOnly: true,
 	}
@@ -57,12 +58,13 @@ func NewExplorer(imageroot string, root string, manifest string, snapshot string
 	}
 
 	return &explorer{
-		imageroot: imageroot,
-		root:      root,
-		manifest:  manifest,
-		snapshot:  snapshot,
-		mdb:       db,
-		sc:        sc,
+		imageroot:  imageroot,
+		root:       root,
+		manifest:   manifest,
+		snapshot:   snapshot,
+		layercache: layercache,
+		mdb:        db,
+		sc:         sc,
 	}, nil
 }
 
@@ -260,7 +262,7 @@ func (e *explorer) ListSnapshots(ctx context.Context) ([]explorers.SnapshotKeyIn
 		}).Error(err)
 	}
 
-	store := NewSnaptshotStore(e.root, e.mdb, ssdb)
+	store := NewSnaptshotStore(e.root, e.layercache, e.mdb, ssdb)
 
 	for _, ns := range nss {
 		ctx = namespaces.WithNamespace(ctx, ns)
@@ -480,7 +482,7 @@ func (e *explorer) MountContainer(ctx context.Context, containerid string, mount
 	}
 
 	// snapshot store
-	ssstore := NewSnaptshotStore(e.root, e.mdb, ssdb)
+	ssstore := NewSnaptshotStore(e.root, e.layercache, e.mdb, ssdb)
 	var mountArgs []string
 	hasWorkDir := false
 	snapshotRoot, _ := filepath.Split(e.snapshot)

explorers/containerd/snapshot.go

@@ -21,6 +21,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io/fs"
+	"os"
 	"path/filepath"
 	"strings"
 
@@ -34,9 +35,10 @@ import (
 )
 
 type snapshotStore struct {
-	root string // containerd root directory
-	db   *bolt.DB
-	sdb  *bolt.DB
+	root       string // containerd root directory
+	layercache string
+	db         *bolt.DB
+	sdb        *bolt.DB
 }
 
 // NewSnapshotStore returns snapshotStore which handles viewing of snapshot information
@@ -54,11 +56,12 @@ type snapshotStore struct {
 // Snapshot path in snapshot database: metadata.db/v1/snapshots/<snapshot key>
 //   - id - Snapshot file system ID i.e. /var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/<id>/fs
 //   - kind - ACTIVE vs COMMITTED
-func NewSnaptshotStore(root string, db *bolt.DB, sdb *bolt.DB) *snapshotStore {
+func NewSnaptshotStore(root string, layercache string, db *bolt.DB, sdb *bolt.DB) *snapshotStore {
 	return &snapshotStore{
-		root: root,
-		db:   db,
-		sdb:  sdb,
+		root:       root,
+		layercache: layercache,
+		db:         db,
+		sdb:        sdb,
 	}
 }
 
@@ -213,13 +216,36 @@ func (s *snapshotStore) OverlayPath(ctx context.Context, container containers.Co
 		upperdir = filepath.Join(snapshotroot, "snapshots", fmt.Sprintf("%d", upperdirID), "fs")
 		workdir = filepath.Join(snapshotroot, "snapshots", fmt.Sprintf("%d", upperdirID), "work")
 
+		if s.layercache != "" {
+			symlink, err := os.Readlink(upperdir)
+			if err == nil {
+				log.WithFields(log.Fields{
+					"id":      upperdirID,
+					"symlink": symlink,
+				}).Debug("upperdir")
+				_, layer := filepath.Split(symlink)
+				upperdir = filepath.Join(snapshotroot, s.layercache, layer)
+			}
+		}
+
 		// compute lowerdir
 		for _, ssk := range snapshotkeys[1:] {
 			id, err := getSnapshotID(tx, ssk)
 			if err != nil {
 				return err
 			}
 			ldir := filepath.Join(snapshotroot, "snapshots", fmt.Sprintf("%d", id), "fs")
+			if s.layercache != "" {
+				symlink, err := os.Readlink(ldir)
+				if err == nil {
+					log.WithFields(log.Fields{
+						"id":      id,
+						"symlink": symlink,
+					}).Debug("layer")
+					_, layer := filepath.Split(symlink)
+					ldir = filepath.Join(snapshotroot, "layers", layer)
+				}
+			}
 
 			if lowerdir == "" {
 				lowerdir = ldir