Move rootfs to pkg/rootfs

Signed-off-by: Derek McGowan <derek@mcg.dev>

pkg/rootfs/init.go

@@ -0,0 +1,116 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package rootfs
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+
+	"github.com/containerd/containerd/v2/core/mount"
+	"github.com/containerd/containerd/v2/core/snapshots"
+	"github.com/containerd/log"
+	digest "github.com/opencontainers/go-digest"
+)
+
+var (
+	initializers = map[string]initializerFunc{}
+)
+
+type initializerFunc func(string) error
+
+// Mounter handles mount and unmount
+type Mounter interface {
+	Mount(target string, mounts ...mount.Mount) error
+	Unmount(target string) error
+}
+
+// InitRootFS initializes the snapshot for use as a rootfs
+func InitRootFS(ctx context.Context, name string, parent digest.Digest, readonly bool, snapshotter snapshots.Snapshotter, mounter Mounter) ([]mount.Mount, error) {
+	_, err := snapshotter.Stat(ctx, name)
+	if err == nil {
+		return nil, errors.New("rootfs already exists")
+	}
+	// TODO: ensure not exist error once added to snapshot package
+
+	parentS := parent.String()
+
+	initName := defaultInitializer
+	initFn := initializers[initName]
+	if initFn != nil {
+		parentS, err = createInitLayer(ctx, parentS, initName, initFn, snapshotter, mounter)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	if readonly {
+		return snapshotter.View(ctx, name, parentS)
+	}
+
+	return snapshotter.Prepare(ctx, name, parentS)
+}
+
+func createInitLayer(ctx context.Context, parent, initName string, initFn func(string) error, snapshotter snapshots.Snapshotter, mounter Mounter) (_ string, retErr error) {
+	initS := fmt.Sprintf("%s %s", parent, initName)
+	if _, err := snapshotter.Stat(ctx, initS); err == nil {
+		return initS, nil
+	}
+	// TODO: ensure not exist error once added to snapshot package
+
+	// Create tempdir
+	td, err := os.MkdirTemp(os.Getenv("XDG_RUNTIME_DIR"), "create-init-")
+	if err != nil {
+		return "", err
+	}
+	defer os.RemoveAll(td)
+
+	mounts, err := snapshotter.Prepare(ctx, td, parent)
+	if err != nil {
+		return "", err
+	}
+
+	defer func() {
+		if retErr != nil {
+			if rerr := snapshotter.Remove(ctx, td); rerr != nil {
+				log.G(ctx).Errorf("Failed to remove snapshot %s: %v", td, rerr)
+			}
+		}
+	}()
+
+	if err = mounter.Mount(td, mounts...); err != nil {
+		return "", err
+	}
+
+	if err = initFn(td); err != nil {
+		if merr := mounter.Unmount(td); merr != nil {
+			log.G(ctx).Errorf("Failed to unmount %s: %v", td, merr)
+		}
+		return "", err
+	}
+
+	if err = mounter.Unmount(td); err != nil {
+		return "", err
+	}
+
+	if err := snapshotter.Commit(ctx, initS, td); err != nil {
+		return "", err
+	}
+
+	return initS, nil
+}