This PR refactors the blob service API to be oriented around blob descriptors. Identified by digests, blobs become an abstract entity that can be read and written using a descriptor as a handle. This allows blobs to take many forms, such as a ReadSeekCloser or a simple byte buffer, allowing blob oriented operations to better integrate with blob agnostic APIs (such as the `io` package). The error definitions are now better organized to reflect conditions that can only be seen when interacting with the blob API. The main benefit of this is to separate the much smaller metadata from large file storage. Many benefits also follow from this. Reading and writing has been separated into discrete services. Backend implementation is also simplified, by reducing the amount of metadata that needs to be picked up to simply serve a read. This also improves cacheability. "Opening" a blob simply consists of an access check (Stat) and a path calculation. Caching is greatly simplified and we've made the mapping of provisional to canonical hashes a first-class concept. BlobDescriptorService and BlobProvider can be combined in different ways to achieve varying effects. Recommend Review Approach ------------------------- This is a very large patch. While apologies are in order, we are getting a considerable amount of refactoring. Most changes follow from the changes to the root package (distribution), so start there. From there, the main changes are in storage. Looking at (*repository).Blobs will help to understand the how the linkedBlobStore is wired. One can explore the internals within and also branch out into understanding the changes to the caching layer. Following the descriptions below will also help to guide you. To reduce the chances for regressions, it was critical that major changes to unit tests were avoided. Where possible, they are left untouched and where not, the spirit is hopefully captured. Pay particular attention to where behavior may have changed. Storage ------- The primary changes to the `storage` package, other than the interface updates, were to merge the layerstore and blobstore. Blob access is now layered even further. The first layer, blobStore, exposes a global `BlobStatter` and `BlobProvider`. Operations here provide a fast path for most read operations that don't take access control into account. The `linkedBlobStore` layers on top of the `blobStore`, providing repository- scoped blob link management in the backend. The `linkedBlobStore` implements the full `BlobStore` suite, providing access-controlled, repository-local blob writers. The abstraction between the two is slightly broken in that `linkedBlobStore` is the only channel under which one can write into the global blob store. The `linkedBlobStore` also provides flexibility in that it can act over different link sets depending on configuration. This allows us to use the same code for signature links, manifest links and blob links. Eventually, we will fully consolidate this storage. The improved cache flow comes from the `linkedBlobStatter` component of `linkedBlobStore`. Using a `cachedBlobStatter`, these combine together to provide a simple cache hierarchy that should streamline access checks on read and write operations, or at least provide a single path to optimize. The metrics have been changed in a slightly incompatible way since the former operations, Fetch and Exists, are no longer relevant. The fileWriter and fileReader have been slightly modified to support the rest of the changes. The most interesting is the removal of the `Stat` call from `newFileReader`. This was the source of unnecessary round trips that were only present to look up the size of the resulting reader. Now, one must simply pass in the size, requiring the caller to decide whether or not the `Stat` call is appropriate. In several cases, it turned out the caller already had the size already. The `WriterAt` implementation has been removed from `fileWriter`, since it is no longer required for `BlobWriter`, reducing the number of paths which writes may take. Cache ----- Unfortunately, the `cache` package required a near full rewrite. It was pretty mechanical in that the cache is oriented around the `BlobDescriptorService` slightly modified to include the ability to set the values for individual digests. While the implementation is oriented towards caching, it can act as a primary store. Provisions are in place to have repository local metadata, in addition to global metadata. Fallback is implemented as a part of the storage package to maintain this flexibility. One unfortunate side-effect is that caching is now repository-scoped, rather than global. This should have little effect on performance but may increase memory usage. Handlers -------- The `handlers` package has been updated to leverage the new API. For the most part, the changes are superficial or mechanical based on the API changes. This did expose a bug in the handling of provisional vs canonical digests that was fixed in the unit tests. Configuration ------------- One user-facing change has been made to the configuration and is updated in the associated documentation. The `layerinfo` cache parameter has been deprecated by the `blobdescriptor` cache parameter. Both are equivalent and configuration files should be backward compatible. Notifications ------------- Changes the `notification` package are simply to support the interface changes. Context ------- A small change has been made to the tracing log-level. Traces have been moved from "info" to "debug" level to reduce output when not needed. Signed-off-by: Stephen J Day <stephen.day@docker.com>
143 lines
3.5 KiB
Go
143 lines
3.5 KiB
Go
package storage
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import (
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"path"
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"github.com/docker/distribution"
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"github.com/docker/distribution/context"
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"github.com/docker/distribution/digest"
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storagedriver "github.com/docker/distribution/registry/storage/driver"
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)
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// tagStore provides methods to manage manifest tags in a backend storage driver.
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type tagStore struct {
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repository *repository
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blobStore *blobStore
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ctx context.Context
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}
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// tags lists the manifest tags for the specified repository.
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func (ts *tagStore) tags() ([]string, error) {
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p, err := ts.blobStore.pm.path(manifestTagPathSpec{
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name: ts.repository.Name(),
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})
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if err != nil {
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return nil, err
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}
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var tags []string
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entries, err := ts.blobStore.driver.List(ts.ctx, p)
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if err != nil {
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switch err := err.(type) {
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case storagedriver.PathNotFoundError:
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return nil, distribution.ErrRepositoryUnknown{Name: ts.repository.Name()}
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default:
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return nil, err
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}
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}
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for _, entry := range entries {
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_, filename := path.Split(entry)
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tags = append(tags, filename)
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}
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return tags, nil
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}
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// exists returns true if the specified manifest tag exists in the repository.
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func (ts *tagStore) exists(tag string) (bool, error) {
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tagPath, err := ts.blobStore.pm.path(manifestTagCurrentPathSpec{
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name: ts.repository.Name(),
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tag: tag,
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})
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if err != nil {
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return false, err
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}
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exists, err := exists(ts.ctx, ts.blobStore.driver, tagPath)
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if err != nil {
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return false, err
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}
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return exists, nil
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}
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// tag tags the digest with the given tag, updating the the store to point at
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// the current tag. The digest must point to a manifest.
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func (ts *tagStore) tag(tag string, revision digest.Digest) error {
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currentPath, err := ts.blobStore.pm.path(manifestTagCurrentPathSpec{
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name: ts.repository.Name(),
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tag: tag,
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})
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if err != nil {
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return err
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}
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nbs := ts.linkedBlobStore(ts.ctx, tag)
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// Link into the index
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if err := nbs.linkBlob(ts.ctx, distribution.Descriptor{Digest: revision}); err != nil {
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return err
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}
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// Overwrite the current link
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return ts.blobStore.link(ts.ctx, currentPath, revision)
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}
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// resolve the current revision for name and tag.
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func (ts *tagStore) resolve(tag string) (digest.Digest, error) {
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currentPath, err := ts.blobStore.pm.path(manifestTagCurrentPathSpec{
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name: ts.repository.Name(),
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tag: tag,
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})
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if err != nil {
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return "", err
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}
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revision, err := ts.blobStore.readlink(ts.ctx, currentPath)
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if err != nil {
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switch err.(type) {
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case storagedriver.PathNotFoundError:
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return "", distribution.ErrManifestUnknown{Name: ts.repository.Name(), Tag: tag}
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}
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return "", err
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}
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return revision, nil
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}
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// delete removes the tag from repository, including the history of all
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// revisions that have the specified tag.
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func (ts *tagStore) delete(tag string) error {
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tagPath, err := ts.blobStore.pm.path(manifestTagPathSpec{
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name: ts.repository.Name(),
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tag: tag,
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})
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if err != nil {
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return err
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}
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return ts.blobStore.driver.Delete(ts.ctx, tagPath)
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}
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// namedBlobStore returns the namedBlobStore for the named tag, allowing one
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// to index manifest blobs by tag name. While the tag store doesn't map
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// precisely to the linked blob store, using this ensures the links are
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// managed via the same code path.
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func (ts *tagStore) linkedBlobStore(ctx context.Context, tag string) *linkedBlobStore {
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return &linkedBlobStore{
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blobStore: ts.blobStore,
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repository: ts.repository,
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ctx: ctx,
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linkPath: func(pm *pathMapper, name string, dgst digest.Digest) (string, error) {
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return pm.path(manifestTagIndexEntryLinkPathSpec{
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name: name,
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tag: tag,
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revision: dgst,
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})
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},
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}
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}
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