add cvmfs filesystem implementation

Makefile

@@ -20,7 +20,7 @@ DOCKER_ARGS ?=
 GO111MODULE_VALUE=off
 PREFIX ?= out/
 
-PLUGINS=stargzfs-linux-amd64.so
+PLUGINS=stargzfs-linux-amd64.so cvmfs-linux-amd64.so
 CMD=rsnapshotd
 
 PLUGIN_BINARIES=$(addprefix $(PREFIX),$(PLUGINS))
@@ -37,6 +37,10 @@ FORCE:
 stargzfs-linux-amd64.so: FORCE
 	GO111MODULE=$(GO111MODULE_VALUE) go build -buildmode=plugin -o $(PREFIX)$@ -v ./filesystems/stargz
 
+cvmfs-linux-amd64.so: FORCE
+	GO111MODULE=$(GO111MODULE_VALUE) go build -buildmode=plugin -o $(PREFIX)$@ -v ./filesystems/cvmfs
+
+
 rsnapshotd: FORCE
 	GO111MODULE=$(GO111MODULE_VALUE) go build -o $(PREFIX)$@ -v ./cmd/rsnapshotd
 

filesystems/cvmfs/fs.go

@@ -0,0 +1,95 @@
+// +build linux
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+
+	"github.com/containerd/containerd/log"
+	"github.com/containerd/containerd/plugin"
+	fsplugin "github.com/ktock/remote-snapshotter/filesystems"
+)
+
+func init() {
+	plugin.Register(&plugin.Registration{
+		Type:   fsplugin.RemoteFileSystemPlugin,
+		Config: &Config{},
+		ID:     "cvmfs",
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			config, ok := ic.Config.(*Config)
+			if !ok {
+				return nil, fmt.Errorf("invalid cvmfs-remote-snapshotter configuration")
+			}
+			ic.Meta.Exports["root"] = ic.Root
+
+			return NewFilesystem(ic.Root, config)
+		},
+	})
+}
+
+type filesystem struct {
+	repository    string
+	mountedLayers map[string]string
+}
+
+type Config struct {
+	Repository string `toml:"repository" default:"unpacked.cern.ch"`
+}
+
+func NewFilesystem(root string, config *Config) (*filesystem, error) {
+	repository := config.Repository
+	if repository == "" {
+		repository = "unpacked.cern.ch"
+	}
+	return &filesystem{repository: repository, mountedLayers: make(map[string]string)}, nil
+}
+
+func (fs *filesystem) Mount(ctx context.Context, ref, digest, mountpoint string) error {
+	digest = strings.Split(digest, ":")[1]
+	firstTwo := digest[0:2]
+	path := filepath.Join("/", "cvmfs", fs.repository, ".layers", firstTwo, digest, "layerfs")
+	if _, err := os.Stat(path); os.IsNotExist(err) {
+		err = fmt.Errorf("layer %s not in the cvmfs repository", digest)
+		log.G(ctx).WithError(err).WithField("layer digest", digest).WithField("path", path).Debug("cvmfs: Layer not found")
+		return err
+	}
+	log.G(ctx).WithField("layer digest", digest).Debug("cvmfs: Layer present in CVMFS")
+	err := syscall.Mount(path, mountpoint, "", syscall.MS_BIND, "")
+	if err != nil {
+		log.G(ctx).WithError(err).WithField("layer digest", digest).WithField("mountpoint", mountpoint).Debug("cvmfs: Error in bind mounting the layer.")
+		return err
+	}
+	fs.mountedLayers[mountpoint] = path
+	return nil
+}
+
+func (fs *filesystem) Check(ctx context.Context, mountpoint string) error {
+	path, ok := fs.mountedLayers[mountpoint]
+	if !ok {
+		err := fmt.Errorf("Mountpoint: %s was not mounted", mountpoint)
+		log.G(ctx).WithError(err).WithField("mountpoint", mountpoint).Error("cvmfs: the requested mountpoint does not seem to be mounted")
+		return err
+	}
+
+	_, statErr := os.Stat(path)
+	if statErr == nil {
+		return nil
+	}
+	if statErr != nil {
+		if os.IsNotExist(statErr) {
+			err := fmt.Errorf("Layer from path: %s does not seems to be in the CVMFS repository")
+			log.G(ctx).WithError(err).WithField("mountpoint", mountpoint).WithField("layer path", path).Error("cvmfs: the mounted layer does not seem to exist.")
+			return err
+		} else {
+			err := fmt.Errorf("Error in stat-ing the layer: %s", statErr)
+			log.G(ctx).WithError(err).WithField("mountpoint", mountpoint).WithField("layer path", path).Error("cvmfs: unknow error in stating the file.")
+			return err
+		}
+	}
+	return statErr
+}

script/demo/config.rsnapshotd.toml

@@ -5,3 +5,4 @@
     lru_max_entry = 5000
     http_cache_type = "directory"
     filesystem_cache_type = "directory"
+  [plugins.cvmfs]

script/demo/docker-compose.yml

@@ -23,6 +23,7 @@ services:
     - /tmp:exec,mode=777
     volumes:
     - /dev/fuse:/dev/fuse
+    - /cvmfs:/cvmfs:shared
     - "${GOPATH}/src/github.com/ktock/remote-snapshotter:/go/src/github.com/ktock/remote-snapshotter:ro"
   registry2:
     image: registry:2