rootfs: fix compilation error

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

vendor/github.com/opencontainers/image-spec/identity/chainid.go

@@ -0,0 +1,67 @@
+// Copyright 2016 The Linux Foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package identity provides implementations of subtle calculations pertaining
+// to image and layer identity.  The primary item present here is the ChainID
+// calculation used in identifying the result of subsequent layer applications.
+//
+// Helpers are also provided here to ease transition to the
+// github.com/opencontainers/go-digest package, but that package may be used
+// directly.
+package identity
+
+import "github.com/opencontainers/go-digest"
+
+// ChainID takes a slice of digests and returns the ChainID corresponding to
+// the last entry. Typically, these are a list of layer DiffIDs, with the
+// result providing the ChainID identifying the result of sequential
+// application of the preceding layers.
+func ChainID(dgsts []digest.Digest) digest.Digest {
+	chainIDs := make([]digest.Digest, len(dgsts))
+	copy(chainIDs, dgsts)
+	ChainIDs(chainIDs)
+
+	if len(chainIDs) == 0 {
+		return ""
+	}
+	return chainIDs[len(chainIDs)-1]
+}
+
+// ChainIDs calculates the recursively applied chain id for each identifier in
+// the slice. The result is written direcly back into the slice such that the
+// ChainID for each item will be in the respective position.
+//
+// By definition of ChainID, the zeroth element will always be the same before
+// and after the call.
+//
+// As an example, given the chain of ids `[A, B, C]`, the result `[A,
+// ChainID(A|B), ChainID(A|B|C)]` will be written back to the slice.
+//
+// The input is provided as a return value for convenience.
+//
+// Typically, these are a list of layer DiffIDs, with the
+// result providing the ChainID for each the result of each layer application
+// sequentially.
+func ChainIDs(dgsts []digest.Digest) []digest.Digest {
+	if len(dgsts) < 2 {
+		return dgsts
+	}
+
+	parent := digest.FromBytes([]byte(dgsts[0] + " " + dgsts[1]))
+	next := dgsts[1:]
+	next[0] = parent
+	ChainIDs(next)
+
+	return dgsts
+}

vendor/github.com/opencontainers/image-spec/identity/helpers.go

@@ -0,0 +1,40 @@
+// Copyright 2016 The Linux Foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package identity
+
+import (
+	_ "crypto/sha256" // side-effect to install impls, sha256
+	_ "crypto/sha512" // side-effect to install impls, sha384/sh512
+
+	"io"
+
+	digest "github.com/opencontainers/go-digest"
+)
+
+// FromReader consumes the content of rd until io.EOF, returning canonical
+// digest.
+func FromReader(rd io.Reader) (digest.Digest, error) {
+	return digest.Canonical.FromReader(rd)
+}
+
+// FromBytes digests the input and returns a Digest.
+func FromBytes(p []byte) digest.Digest {
+	return digest.Canonical.FromBytes(p)
+}
+
+// FromString digests the input and returns a Digest.
+func FromString(s string) digest.Digest {
+	return digest.Canonical.FromString(s)
+}