Move rootfs to pkg/rootfs

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

pkg/rootfs/apply.go

@@ -0,0 +1,186 @@
+/*
+   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"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"time"
+
+	"github.com/containerd/containerd/v2/core/diff"
+	"github.com/containerd/containerd/v2/core/mount"
+	"github.com/containerd/containerd/v2/core/snapshots"
+	"github.com/containerd/containerd/v2/pkg/errdefs"
+	"github.com/containerd/log"
+	"github.com/opencontainers/go-digest"
+	"github.com/opencontainers/image-spec/identity"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+// Layer represents the descriptors for a layer diff. These descriptions
+// include the descriptor for the uncompressed tar diff as well as a blob
+// used to transport that tar. The blob descriptor may or may not describe
+// a compressed object.
+type Layer struct {
+	Diff ocispec.Descriptor
+	Blob ocispec.Descriptor
+}
+
+// ApplyLayers applies all the layers using the given snapshotter and applier.
+// The returned result is a chain id digest representing all the applied layers.
+// Layers are applied in order they are given, making the first layer the
+// bottom-most layer in the layer chain.
+func ApplyLayers(ctx context.Context, layers []Layer, sn snapshots.Snapshotter, a diff.Applier) (digest.Digest, error) {
+	return ApplyLayersWithOpts(ctx, layers, sn, a, nil)
+}
+
+// ApplyLayersWithOpts applies all the layers using the given snapshotter, applier, and apply opts.
+// The returned result is a chain id digest representing all the applied layers.
+// Layers are applied in order they are given, making the first layer the
+// bottom-most layer in the layer chain.
+func ApplyLayersWithOpts(ctx context.Context, layers []Layer, sn snapshots.Snapshotter, a diff.Applier, applyOpts []diff.ApplyOpt) (digest.Digest, error) {
+	chain := make([]digest.Digest, len(layers))
+	for i, layer := range layers {
+		chain[i] = layer.Diff.Digest
+	}
+	chainID := identity.ChainID(chain)
+
+	// Just stat top layer, remaining layers will have their existence checked
+	// on prepare. Calling prepare on upper layers first guarantees that upper
+	// layers are not removed while calling stat on lower layers
+	_, err := sn.Stat(ctx, chainID.String())
+	if err != nil {
+		if !errdefs.IsNotFound(err) {
+			return "", fmt.Errorf("failed to stat snapshot %s: %w", chainID, err)
+		}
+
+		if err := applyLayers(ctx, layers, chain, sn, a, nil, applyOpts); err != nil && !errdefs.IsAlreadyExists(err) {
+			return "", err
+		}
+	}
+
+	return chainID, nil
+}
+
+// ApplyLayer applies a single layer on top of the given provided layer chain,
+// using the provided snapshotter and applier. If the layer was unpacked true
+// is returned, if the layer already exists false is returned.
+func ApplyLayer(ctx context.Context, layer Layer, chain []digest.Digest, sn snapshots.Snapshotter, a diff.Applier, opts ...snapshots.Opt) (bool, error) {
+	return ApplyLayerWithOpts(ctx, layer, chain, sn, a, opts, nil)
+}
+
+// ApplyLayerWithOpts applies a single layer on top of the given provided layer chain,
+// using the provided snapshotter, applier, and apply opts. If the layer was unpacked true
+// is returned, if the layer already exists false is returned.
+func ApplyLayerWithOpts(ctx context.Context, layer Layer, chain []digest.Digest, sn snapshots.Snapshotter, a diff.Applier, opts []snapshots.Opt, applyOpts []diff.ApplyOpt) (bool, error) {
+	var (
+		chainID = identity.ChainID(append(chain, layer.Diff.Digest)).String()
+		applied bool
+	)
+	if _, err := sn.Stat(ctx, chainID); err != nil {
+		if !errdefs.IsNotFound(err) {
+			return false, fmt.Errorf("failed to stat snapshot %s: %w", chainID, err)
+		}
+
+		if err := applyLayers(ctx, []Layer{layer}, append(chain, layer.Diff.Digest), sn, a, opts, applyOpts); err != nil {
+			if !errdefs.IsAlreadyExists(err) {
+				return false, err
+			}
+		} else {
+			applied = true
+		}
+	}
+	return applied, nil
+
+}
+
+func applyLayers(ctx context.Context, layers []Layer, chain []digest.Digest, sn snapshots.Snapshotter, a diff.Applier, opts []snapshots.Opt, applyOpts []diff.ApplyOpt) error {
+	var (
+		parent  = identity.ChainID(chain[:len(chain)-1])
+		chainID = identity.ChainID(chain)
+		layer   = layers[len(layers)-1]
+		diff    ocispec.Descriptor
+		key     string
+		mounts  []mount.Mount
+		err     error
+	)
+
+	for {
+		key = fmt.Sprintf(snapshots.UnpackKeyFormat, uniquePart(), chainID)
+
+		// Prepare snapshot with from parent, label as root
+		mounts, err = sn.Prepare(ctx, key, parent.String(), opts...)
+		if err != nil {
+			if errdefs.IsNotFound(err) && len(layers) > 1 {
+				if err := applyLayers(ctx, layers[:len(layers)-1], chain[:len(chain)-1], sn, a, opts, applyOpts); err != nil {
+					if !errdefs.IsAlreadyExists(err) {
+						return err
+					}
+				}
+				// Do no try applying layers again
+				layers = nil
+				continue
+			} else if errdefs.IsAlreadyExists(err) {
+				// Try a different key
+				continue
+			}
+
+			// Already exists should have the caller retry
+			return fmt.Errorf("failed to prepare extraction snapshot %q: %w", key, err)
+
+		}
+		break
+	}
+	defer func() {
+		if err != nil {
+			if !errdefs.IsAlreadyExists(err) {
+				log.G(ctx).WithError(err).WithField("key", key).Infof("apply failure, attempting cleanup")
+			}
+
+			if rerr := sn.Remove(ctx, key); rerr != nil {
+				log.G(ctx).WithError(rerr).WithField("key", key).Warnf("extraction snapshot removal failed")
+			}
+		}
+	}()
+
+	diff, err = a.Apply(ctx, layer.Blob, mounts, applyOpts...)
+	if err != nil {
+		err = fmt.Errorf("failed to extract layer %s: %w", layer.Diff.Digest, err)
+		return err
+	}
+	if diff.Digest != layer.Diff.Digest {
+		err = fmt.Errorf("wrong diff id calculated on extraction %q", diff.Digest)
+		return err
+	}
+
+	if err = sn.Commit(ctx, chainID.String(), key, opts...); err != nil {
+		err = fmt.Errorf("failed to commit snapshot %s: %w", key, err)
+		return err
+	}
+
+	return nil
+}
+
+func uniquePart() string {
+	t := time.Now()
+	var b [3]byte
+	// Ignore read failures, just decreases uniqueness
+	rand.Read(b[:])
+	return fmt.Sprintf("%d-%s", t.Nanosecond(), base64.URLEncoding.EncodeToString(b[:]))
+}