597d0d76ae
Prevent unpack failures due to id collision or the need to wait for another process to finish unpacking. Always attempt to unpack a layer and handle collisions on commit. Commit collisions are easily handled as it could be considered the same as a successful unpack. Signed-off-by: Derek McGowan <derek@mcgstyle.net>
118 lines
3.8 KiB
Go
118 lines
3.8 KiB
Go
package rootfs
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import (
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"crypto/rand"
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"encoding/base64"
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"fmt"
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"time"
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"github.com/containerd/containerd/errdefs"
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"github.com/containerd/containerd/log"
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"github.com/containerd/containerd/mount"
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"github.com/containerd/containerd/snapshot"
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"github.com/opencontainers/go-digest"
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"github.com/opencontainers/image-spec/identity"
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ocispec "github.com/opencontainers/image-spec/specs-go/v1"
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"github.com/pkg/errors"
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"golang.org/x/net/context"
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)
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// Applier is used to apply a descriptor of a layer diff on top of mounts.
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type Applier interface {
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Apply(context.Context, ocispec.Descriptor, []mount.Mount) (ocispec.Descriptor, error)
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}
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// Layer represents the descriptors for a layer diff. These descriptions
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// include the descriptor for the uncompressed tar diff as well as a blob
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// used to transport that tar. The blob descriptor may or may not describe
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// a compressed object.
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type Layer struct {
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Diff ocispec.Descriptor
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Blob ocispec.Descriptor
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}
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// ApplyLayers applies all the layers using the given snapshotter and applier.
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// The returned result is a chain id digest representing all the applied layers.
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// Layers are applied in order they are given, making the first layer the
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// bottom-most layer in the layer chain.
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func ApplyLayers(ctx context.Context, layers []Layer, sn snapshot.Snapshotter, a Applier) (digest.Digest, error) {
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var chain []digest.Digest
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for _, layer := range layers {
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if _, err := ApplyLayer(ctx, layer, chain, sn, a); err != nil {
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// TODO: possibly wait and retry if extraction of same chain id was in progress
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return "", err
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}
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chain = append(chain, layer.Diff.Digest)
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}
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return identity.ChainID(chain), nil
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}
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// ApplyLayer applies a single layer on top of the given provided layer chain,
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// using the provided snapshotter and applier. If the layer was unpacked true
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// is returned, if the layer already exists false is returned.
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func ApplyLayer(ctx context.Context, layer Layer, chain []digest.Digest, sn snapshot.Snapshotter, a Applier) (bool, error) {
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var (
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parent = identity.ChainID(chain)
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chainID = identity.ChainID(append(chain, layer.Diff.Digest))
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diff ocispec.Descriptor
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)
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_, err := sn.Stat(ctx, chainID.String())
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if err == nil {
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log.G(ctx).Debugf("Extraction not needed, layer snapshot exists")
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return false, nil
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} else if !errdefs.IsNotFound(err) {
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return false, errors.Wrap(err, "failed to stat snapshot")
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}
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key := fmt.Sprintf("extract-%s %s", uniquePart(), chainID)
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// Prepare snapshot with from parent
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mounts, err := sn.Prepare(ctx, key, parent.String())
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if err != nil {
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//TODO: If is snapshot exists error, retry
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return false, errors.Wrap(err, "failed to prepare extraction layer")
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}
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defer func() {
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if err != nil {
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log.G(ctx).WithError(err).WithField("key", key).Infof("Apply failure, attempting cleanup")
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if rerr := sn.Remove(ctx, key); rerr != nil {
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log.G(ctx).WithError(rerr).Warnf("Extraction snapshot %q removal failed", key)
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}
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}
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}()
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diff, err = a.Apply(ctx, layer.Blob, mounts)
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if err != nil {
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return false, errors.Wrapf(err, "failed to extract layer %s", layer.Diff.Digest)
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}
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if diff.Digest != layer.Diff.Digest {
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err = errors.Errorf("wrong diff id calculated on extraction %q", diff.Digest)
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return false, err
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}
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if err = sn.Commit(ctx, chainID.String(), key); err != nil {
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if !errdefs.IsAlreadyExists(err) {
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return false, errors.Wrapf(err, "failed to commit snapshot %s", parent)
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}
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// Destination already exists, cleanup key and return without error
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err = nil
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if err := sn.Remove(ctx, key); err != nil {
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return false, errors.Wrapf(err, "failed to cleanup aborted apply %s", key)
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}
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return false, nil
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}
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return true, nil
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}
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func uniquePart() string {
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t := time.Now()
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var b [3]byte
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// Ignore read failures, just decreases uniqueness
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rand.Read(b[:])
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return fmt.Sprintf("%d-%s", t.Nanosecond(), base64.URLEncoding.EncodeToString(b[:]))
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}
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