archive: Optimize ChangesDirs on Linux

If we tear through a few layers of abstraction, we can get at the inodes
contained in a directory without having to stat all the files. This
allows us to eliminate identical files much earlier in the changelist
generation process.

Signed-off-by: Burke Libbey <burke@libbey.me>

archive/changes_other.go

@@ -0,0 +1,84 @@
+// +build !linux
+
+package archive
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/docker/docker/pkg/system"
+)
+
+func collectFileInfoForChanges(oldDir, newDir string) (*FileInfo, *FileInfo, error) {
+	var (
+		oldRoot, newRoot *FileInfo
+		err1, err2       error
+		errs             = make(chan error, 2)
+	)
+	go func() {
+		oldRoot, err1 = collectFileInfo(oldDir)
+		errs <- err1
+	}()
+	go func() {
+		newRoot, err2 = collectFileInfo(newDir)
+		errs <- err2
+	}()
+
+	// block until both routines have returned
+	for i := 0; i < 2; i++ {
+		if err := <-errs; err != nil {
+			return nil, nil, err
+		}
+	}
+
+	return oldRoot, newRoot, nil
+}
+
+func collectFileInfo(sourceDir string) (*FileInfo, error) {
+	root := newRootFileInfo()
+
+	err := filepath.Walk(sourceDir, func(path string, f os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		// Rebase path
+		relPath, err := filepath.Rel(sourceDir, path)
+		if err != nil {
+			return err
+		}
+		relPath = filepath.Join("/", relPath)
+
+		if relPath == "/" {
+			return nil
+		}
+
+		parent := root.LookUp(filepath.Dir(relPath))
+		if parent == nil {
+			return fmt.Errorf("collectFileInfo: Unexpectedly no parent for %s", relPath)
+		}
+
+		info := &FileInfo{
+			name:     filepath.Base(relPath),
+			children: make(map[string]*FileInfo),
+			parent:   parent,
+		}
+
+		s, err := system.Lstat(path)
+		if err != nil {
+			return err
+		}
+		info.stat = s
+
+		info.capability, _ = system.Lgetxattr(path, "security.capability")
+
+		parent.children[info.name] = info
+
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return root, nil
+}