Merge pull request #222 from jonboulle/hardlinks

actool: properly deal with hardlinks when building images

app-container/actool/build.go

@@ -37,6 +37,8 @@ func init() {
 }
 
 func buildWalker(root string, aw aci.ArchiveWriter, rootfs bool) filepath.WalkFunc {
+	// cache of inode -> filepath, used to leverage hard links in the archive
+	inos := map[uint64]string{}
 	return func(path string, info os.FileInfo, err error) error {
 		if err != nil {
 			return err
@@ -81,7 +83,12 @@ func buildWalker(root string, aw aci.ArchiveWriter, rootfs bool) filepath.WalkFu
 		// modify the Name field of the returned header to provide the
 		// full path name of the file.
 		hdr.Name = relpath
-		tarheader.Populate(hdr, info)
+		tarheader.Populate(hdr, info, inos)
+		// If the file is a hard link we don't need the contents
+		if hdr.Typeflag == tar.TypeLink {
+			hdr.Size = 0
+			file = nil
+		}
 		aw.AddFile(relpath, hdr, file)
 
 		return nil

pkg/tarheader/pop_darwin.go

@@ -13,7 +13,7 @@ func init() {
 	populateHeaderStat = append(populateHeaderStat, populateHeaderCtime)
 }
 
-func populateHeaderCtime(h *tar.Header, fi os.FileInfo) {
+func populateHeaderCtime(h *tar.Header, fi os.FileInfo, _ map[uint64]string) {
 	st, ok := fi.Sys().(*syscall.Stat_t)
 	if !ok {
 		return

pkg/tarheader/pop_linux.go

@@ -11,7 +11,7 @@ func init() {
 	populateHeaderStat = append(populateHeaderStat, populateHeaderCtime)
 }
 
-func populateHeaderCtime(h *tar.Header, fi os.FileInfo) {
+func populateHeaderCtime(h *tar.Header, fi os.FileInfo, _ map[uint64]string) {
 	st, ok := fi.Sys().(*syscall.Stat_t)
 	if !ok {
 		return

pkg/tarheader/pop_posix.go

@@ -10,11 +10,19 @@ func init() {
 	populateHeaderStat = append(populateHeaderStat, populateHeaderUnix)
 }
 
-func populateHeaderUnix(h *tar.Header, fi os.FileInfo) {
+func populateHeaderUnix(h *tar.Header, fi os.FileInfo, seen map[uint64]string) {
 	st, ok := fi.Sys().(*syscall.Stat_t)
 	if !ok {
 		return
 	}
 	h.Uid = int(st.Uid)
 	h.Gid = int(st.Gid)
+	// If we have already seen this inode, generate a hardlink
+	p, ok := seen[uint64(st.Ino)]
+	if ok {
+		h.Linkname = p
+		h.Typeflag = tar.TypeLink
+	} else {
+		seen[uint64(st.Ino)] = h.Name
+	}
 }

pkg/tarheader/tarheader.go

@@ -5,10 +5,10 @@ import (
 	"os"
 )
 
-var populateHeaderStat []func(h *tar.Header, fi os.FileInfo)
+var populateHeaderStat []func(h *tar.Header, fi os.FileInfo, seen map[uint64]string)
 
-func Populate(h *tar.Header, fi os.FileInfo) {
+func Populate(h *tar.Header, fi os.FileInfo, seen map[uint64]string) {
 	for _, pop := range populateHeaderStat {
-		pop(h, fi)
+		pop(h, fi, seen)
 	}
 }