leverage file locks for cache index.json

Signed-off-by: Avi Deitcher <avi@deitcher.net>

src/cmd/linuxkit/cache/cacheindex.go

@@ -6,13 +6,19 @@ package cache
 import (
 	"errors"
 	"fmt"
+	"path/filepath"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/match"
+	"github.com/linuxkit/linuxkit/src/cmd/linuxkit/util"
 	imagespec "github.com/opencontainers/image-spec/specs-go/v1"
 	log "github.com/sirupsen/logrus"
 )
 
+const (
+	indexFile = "index.json"
+)
+
 // DescriptorWrite writes a descriptor to the cache index; it validates that it has a name
 // and replaces any existing one
 func (p *Provider) DescriptorWrite(image string, desc v1.Descriptor) error {
@@ -25,6 +31,17 @@ func (p *Provider) DescriptorWrite(image string, desc v1.Descriptor) error {
 	desc.Annotations[imagespec.AnnotationRefName] = image
 	log.Debugf("writing descriptor for image %s", image)
 
+	// get our lock
+	lock, err := util.Lock(filepath.Join(p.dir, indexFile))
+	if err != nil {
+		return fmt.Errorf("unable to lock cache index for writing descriptor for %s: %v", image, err)
+	}
+	defer func() {
+		if err := lock.Unlock(); err != nil {
+			log.Errorf("unable to close lock for cache index after writing descriptor for %s: %v", image, err)
+		}
+	}()
+
 	// do we update an existing one? Or create a new one?
 	if err := p.cache.RemoveDescriptors(match.Name(image)); err != nil {
 		return fmt.Errorf("unable to remove old descriptors for %s: %v", image, err)
@@ -40,6 +57,15 @@ func (p *Provider) DescriptorWrite(image string, desc v1.Descriptor) error {
 // RemoveDescriptors removes all descriptors that match the provided matcher.
 // It does so in a parallel-access-safe way
 func (p *Provider) RemoveDescriptors(matcher match.Matcher) error {
-	// will be replaced with locking
+	// get our lock
+	lock, err := util.Lock(filepath.Join(p.dir, indexFile))
+	if err != nil {
+		return fmt.Errorf("unable to lock cache index for removing descriptor for %v: %v", matcher, err)
+	}
+	defer func() {
+		if err := lock.Unlock(); err != nil {
+			log.Errorf("unable to close lock for cache index after writing descriptor for %v: %v", matcher, err)
+		}
+	}()
 	return p.cache.RemoveDescriptors(matcher)
 }

src/cmd/linuxkit/cache/open.go

@@ -2,9 +2,12 @@ package cache
 
 import (
 	"fmt"
+	"path/filepath"
 
 	"github.com/google/go-containerregistry/pkg/v1/empty"
 	"github.com/google/go-containerregistry/pkg/v1/layout"
+	"github.com/linuxkit/linuxkit/src/cmd/linuxkit/util"
+	log "github.com/sirupsen/logrus"
 )
 
 // Get get or initialize the cache
@@ -12,6 +15,15 @@ func Get(cache string) (layout.Path, error) {
 	// initialize the cache path if needed
 	p, err := layout.FromPath(cache)
 	if err != nil {
+		lock, err := util.Lock(filepath.Join(cache, indexFile))
+		if err != nil {
+			return "", fmt.Errorf("unable to lock cache index for writing descriptor for new cache: %v", err)
+		}
+		defer func() {
+			if err := lock.Unlock(); err != nil {
+				log.Errorf("unable to close lock for cache index after writing descriptor for new cache: %v", err)
+			}
+		}()
 		p, err = layout.Write(cache, empty.Index)
 		if err != nil {
 			return p, fmt.Errorf("could not initialize cache at path %s: %v", cache, err)

src/cmd/linuxkit/cache/provider.go

@@ -10,6 +10,7 @@ import (
 type Provider struct {
 	cache layout.Path
 	store content.Store
+	dir   string
 }
 
 // NewProvider create a new CacheProvider based in the provided directory
@@ -22,5 +23,5 @@ func NewProvider(dir string) (*Provider, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &Provider{p, store}, nil
+	return &Provider{p, store, dir}, nil
 }