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image_commit.go
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image_commit.go
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package containerd
import (
"context"
"crypto/rand"
"encoding/base64"
"encoding/json"
"fmt"
"runtime"
"strings"
"time"
"github.com/containerd/containerd/content"
"github.com/containerd/containerd/diff"
cerrdefs "github.com/containerd/containerd/errdefs"
"github.com/containerd/containerd/leases"
"github.com/containerd/containerd/mount"
"github.com/containerd/containerd/pkg/cleanup"
"github.com/containerd/containerd/snapshots"
"github.com/containerd/log"
"github.com/docker/docker/api/types/backend"
"github.com/docker/docker/image"
"github.com/docker/docker/internal/compatcontext"
"github.com/docker/docker/pkg/archive"
imagespec "github.com/moby/docker-image-spec/specs-go/v1"
"github.com/opencontainers/go-digest"
"github.com/opencontainers/image-spec/identity"
ocispec "github.com/opencontainers/image-spec/specs-go/v1"
"github.com/pkg/errors"
)
/*
This code is based on `commit` support in nerdctl, under Apache License
https://github.com/containerd/nerdctl/blob/master/pkg/imgutil/commit/commit.go
with adaptations to match the Moby data model and services.
*/
// CommitImage creates a new image from a commit config.
func (i *ImageService) CommitImage(ctx context.Context, cc backend.CommitConfig) (image.ID, error) {
container := i.containers.Get(cc.ContainerID)
cs := i.content
var parentManifest ocispec.Manifest
var parentImage imagespec.DockerOCIImage
// ImageManifest can be nil when committing an image with base FROM scratch
if container.ImageManifest != nil {
imageManifestBytes, err := content.ReadBlob(ctx, cs, *container.ImageManifest)
if err != nil {
return "", err
}
if err := json.Unmarshal(imageManifestBytes, &parentManifest); err != nil {
return "", err
}
imageConfigBytes, err := content.ReadBlob(ctx, cs, parentManifest.Config)
if err != nil {
return "", err
}
if err := json.Unmarshal(imageConfigBytes, &parentImage); err != nil {
return "", err
}
}
var (
differ = i.client.DiffService()
sn = i.client.SnapshotService(container.Driver)
)
// Don't gc me and clean the dirty data after 1 hour!
ctx, release, err := i.client.WithLease(ctx, leases.WithRandomID(), leases.WithExpiration(1*time.Hour))
if err != nil {
return "", fmt.Errorf("failed to create lease for commit: %w", err)
}
defer func() {
if err := release(compatcontext.WithoutCancel(ctx)); err != nil {
log.G(ctx).WithError(err).Warn("failed to release lease created for commit")
}
}()
diffLayerDesc, diffID, err := i.createDiff(ctx, cc.ContainerID, sn, cs, differ)
if err != nil {
return "", fmt.Errorf("failed to export layer: %w", err)
}
imageConfig := generateCommitImageConfig(parentImage, diffID, cc)
layers := parentManifest.Layers
if diffLayerDesc != nil {
rootfsID := identity.ChainID(imageConfig.RootFS.DiffIDs).String()
if err := i.applyDiffLayer(ctx, rootfsID, cc.ContainerID, sn, differ, *diffLayerDesc); err != nil {
return "", fmt.Errorf("failed to apply diff: %w", err)
}
layers = append(layers, *diffLayerDesc)
}
return i.createImageOCI(ctx, imageConfig, digest.Digest(cc.ParentImageID), layers, *cc.ContainerConfig)
}
// generateCommitImageConfig generates an OCI Image config based on the
// container's image and the CommitConfig options.
func generateCommitImageConfig(baseConfig imagespec.DockerOCIImage, diffID digest.Digest, opts backend.CommitConfig) imagespec.DockerOCIImage {
if opts.Author == "" {
opts.Author = baseConfig.Author
}
createdTime := time.Now()
arch := baseConfig.Architecture
if arch == "" {
arch = runtime.GOARCH
log.G(context.TODO()).Warnf("assuming arch=%q", arch)
}
os := baseConfig.OS
if os == "" {
os = runtime.GOOS
log.G(context.TODO()).Warnf("assuming os=%q", os)
}
log.G(context.TODO()).Debugf("generateCommitImageConfig(): arch=%q, os=%q", arch, os)
diffIds := baseConfig.RootFS.DiffIDs
if diffID != "" {
diffIds = append(diffIds, diffID)
}
return imagespec.DockerOCIImage{
Image: ocispec.Image{
Platform: ocispec.Platform{
Architecture: arch,
OS: os,
},
Created: &createdTime,
Author: opts.Author,
RootFS: ocispec.RootFS{
Type: "layers",
DiffIDs: diffIds,
},
History: append(baseConfig.History, ocispec.History{
Created: &createdTime,
CreatedBy: strings.Join(opts.ContainerConfig.Cmd, " "),
Author: opts.Author,
Comment: opts.Comment,
EmptyLayer: diffID == "",
}),
},
Config: containerConfigToDockerOCIImageConfig(opts.Config),
}
}
// createDiff creates a layer diff into containerd's content store.
// If the diff is empty it returns nil empty digest and no error.
func (i *ImageService) createDiff(ctx context.Context, name string, sn snapshots.Snapshotter, cs content.Store, comparer diff.Comparer) (*ocispec.Descriptor, digest.Digest, error) {
info, err := sn.Stat(ctx, name)
if err != nil {
return nil, "", err
}
var upper []mount.Mount
if !i.idMapping.Empty() {
// The rootfs of the container is remapped if an id mapping exists, we
// need to "unremap" it before committing the snapshot
rootPair := i.idMapping.RootPair()
usernsID := fmt.Sprintf("%s-%d-%d-%s", name, rootPair.UID, rootPair.GID, uniquePart())
remappedID := usernsID + remapSuffix
baseName := name
if info.Kind == snapshots.KindActive {
source, err := sn.Mounts(ctx, name)
if err != nil {
return nil, "", err
}
// No need to use parent since the whole snapshot is copied.
// Using parent would require doing diff/apply while starting
// from empty can just copy the whole snapshot.
// TODO: Optimize this for overlay mounts, can use parent
// and just copy upper directories without mounting
upper, err = sn.Prepare(ctx, remappedID, "")
if err != nil {
return nil, "", err
}
if err := i.copyAndUnremapRootFS(ctx, upper, source); err != nil {
return nil, "", err
}
} else {
upper, err = sn.Prepare(ctx, remappedID, baseName)
if err != nil {
return nil, "", err
}
if err := i.unremapRootFS(ctx, upper); err != nil {
return nil, "", err
}
}
} else {
if info.Kind == snapshots.KindActive {
upper, err = sn.Mounts(ctx, name)
if err != nil {
return nil, "", err
}
} else {
upperKey := fmt.Sprintf("%s-view-%s", name, uniquePart())
upper, err = sn.View(ctx, upperKey, name)
if err != nil {
return nil, "", err
}
defer cleanup.Do(ctx, func(ctx context.Context) {
sn.Remove(ctx, upperKey)
})
}
}
lowerKey := fmt.Sprintf("%s-parent-view-%s", info.Parent, uniquePart())
lower, err := sn.View(ctx, lowerKey, info.Parent)
if err != nil {
return nil, "", err
}
defer cleanup.Do(ctx, func(ctx context.Context) {
sn.Remove(ctx, lowerKey)
})
newDesc, err := comparer.Compare(ctx, lower, upper)
if err != nil {
return nil, "", errors.Wrap(err, "CreateDiff")
}
ra, err := cs.ReaderAt(ctx, newDesc)
if err != nil {
return nil, "", fmt.Errorf("failed to read diff archive: %w", err)
}
defer ra.Close()
empty, err := archive.IsEmpty(content.NewReader(ra))
if err != nil {
return nil, "", fmt.Errorf("failed to check if archive is empty: %w", err)
}
if empty {
return nil, "", nil
}
cinfo, err := cs.Info(ctx, newDesc.Digest)
if err != nil {
return nil, "", fmt.Errorf("failed to get content info: %w", err)
}
diffIDStr, ok := cinfo.Labels["containerd.io/uncompressed"]
if !ok {
return nil, "", fmt.Errorf("invalid differ response with no diffID")
}
diffID, err := digest.Parse(diffIDStr)
if err != nil {
return nil, "", err
}
return &ocispec.Descriptor{
MediaType: ocispec.MediaTypeImageLayerGzip,
Digest: newDesc.Digest,
Size: cinfo.Size,
}, diffID, nil
}
// applyDiffLayer will apply diff layer content created by createDiff into the snapshotter.
func (i *ImageService) applyDiffLayer(ctx context.Context, name string, containerID string, sn snapshots.Snapshotter, differ diff.Applier, diffDesc ocispec.Descriptor) (retErr error) {
// Let containerd know that this snapshot is only for diff-applying.
key := snapshots.UnpackKeyPrefix + "-" + uniquePart() + "-" + name
info, err := sn.Stat(ctx, containerID)
if err != nil {
return err
}
mounts, err := sn.Prepare(ctx, key, info.Parent)
if err != nil {
return fmt.Errorf("failed to prepare snapshot: %w", err)
}
defer func() {
if retErr != nil {
// NOTE: the snapshotter should be held by lease. Even
// if the cleanup fails, the containerd gc can delete it.
if err := sn.Remove(ctx, key); err != nil {
log.G(ctx).Warnf("failed to cleanup aborted apply %s: %s", key, err)
}
}
}()
if _, err = differ.Apply(ctx, diffDesc, mounts); err != nil {
return err
}
if err = sn.Commit(ctx, name, key); err != nil {
if cerrdefs.IsAlreadyExists(err) {
return nil
}
return err
}
return nil
}
// copied from github.com/containerd/containerd/rootfs/apply.go
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[:]))
}
// CommitBuildStep is used by the builder to create an image for each step in
// the build.
//
// This method is different from CreateImageFromContainer:
// - it doesn't attempt to validate container state
// - it doesn't send a commit action to metrics
// - it doesn't log a container commit event
//
// This is a temporary shim. Should be removed when builder stops using commit.
func (i *ImageService) CommitBuildStep(ctx context.Context, c backend.CommitConfig) (image.ID, error) {
ctr := i.containers.Get(c.ContainerID)
if ctr == nil {
// TODO: use typed error
return "", fmt.Errorf("container not found: %s", c.ContainerID)
}
c.ContainerMountLabel = ctr.MountLabel
c.ContainerOS = ctr.OS
c.ParentImageID = string(ctr.ImageID)
return i.CommitImage(ctx, c)
}