diff --git a/exporter/containerimage/exptypes/types.go b/exporter/containerimage/exptypes/types.go
index eddb4d30fbe5e..b98bf97d5a006 100644
--- a/exporter/containerimage/exptypes/types.go
+++ b/exporter/containerimage/exptypes/types.go
@@ -26,15 +26,26 @@ type Platform struct {
 	Platform ocispecs.Platform
 }
 
+// BuildInfo defines build dependencies that will be added to image config as
+// moby.buildkit.buildinfo.v0 key and returned in solver ExporterResponse as
+// ExporterBuildInfo key.
 type BuildInfo struct {
-	Type  BuildInfoType `json:"type,omitempty"`
-	Ref   string        `json:"ref,omitempty"`
-	Alias string        `json:"alias,omitempty"`
-	Pin   string        `json:"pin,omitempty"`
+	// Type defines the BuildInfoType source type (docker-image, git, http).
+	Type BuildInfoType `json:"type,omitempty"`
+	// Ref is the reference of the source type.
+	Ref string `json:"ref,omitempty"`
+	// Alias is a special field used to match with the actual source ref
+	// because frontend might have already transformed a string user typed
+	// before generating LLB.
+	Alias string `json:"alias,omitempty"`
+	// Pin is the source digest.
+	Pin string `json:"pin,omitempty"`
 }
 
+// BuildInfoType contains source type.
 type BuildInfoType string
 
+// List of source types.
 const (
 	BuildInfoTypeDockerImage BuildInfoType = "docker-image"
 	BuildInfoTypeGit         BuildInfoType = "git"
diff --git a/frontend/dockerfile/dockerfile2llb/convert.go b/frontend/dockerfile/dockerfile2llb/convert.go
index c7de217d42891..66bf33c560381 100644
--- a/frontend/dockerfile/dockerfile2llb/convert.go
+++ b/frontend/dockerfile/dockerfile2llb/convert.go
@@ -295,6 +295,8 @@ func Dockerfile2LLB(ctx context.Context, dt []byte, opt ConvertOpt) (*llb.State,
 							}
 						}
 						if !isScratch {
+							// image not scratch set original image name as ref
+							// and actual reference as alias in BuildInfo
 							d.buildInfo = &exptypes.BuildInfo{
 								Type:  exptypes.BuildInfoTypeDockerImage,
 								Ref:   origName,
@@ -411,7 +413,7 @@ func Dockerfile2LLB(ctx context.Context, dt []byte, opt ConvertOpt) (*llb.State,
 		}
 	}
 
-	// Set target with gathered build dependencies
+	// set target with gathered build dependencies
 	target.image.BuildInfo = []byte{}
 	if len(buildInfos) > 0 {
 		target.image.BuildInfo, err = json.Marshal(buildInfos)
diff --git a/frontend/dockerfile/dockerfile2llb/image.go b/frontend/dockerfile/dockerfile2llb/image.go
index 418d2b503a582..c252332d4c73f 100644
--- a/frontend/dockerfile/dockerfile2llb/image.go
+++ b/frontend/dockerfile/dockerfile2llb/image.go
@@ -54,7 +54,7 @@ type Image struct {
 	// Variant defines platform variant. To be added to OCI.
 	Variant string `json:"variant,omitempty"`
 
-	// BuildInfo defines build dependencies
+	// BuildInfo defines build dependencies.
 	BuildInfo []byte `json:"moby.buildkit.buildinfo.v0,omitempty"`
 }