pkg/archive: sort files

sort changes found and exported.

Sorting the files before appending them to the tar archive
would mean a dependable ordering for types like hardlinks.

Also, combine sort logic used

Signed-off-by: Vincent Batts <vbatts@redhat.com>

archive/changes.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 	"syscall"
 	"time"
@@ -43,6 +44,13 @@ func (change *Change) String() string {
 	return fmt.Sprintf("%s %s", kind, change.Path)
 }
 
+// for sort.Sort
+type changesByPath []Change
+
+func (c changesByPath) Less(i, j int) bool { return c[i].Path < c[j].Path }
+func (c changesByPath) Len() int           { return len(c) }
+func (c changesByPath) Swap(i, j int)      { c[j], c[i] = c[i], c[j] }
+
 // Gnu tar and the go tar writer don't have sub-second mtime
 // precision, which is problematic when we apply changes via tar
 // files, we handle this by comparing for exact times, *or* same
@@ -373,6 +381,8 @@ func ExportChanges(dir string, changes []Change) (Archive, error) {
 		// this buffer is needed for the duration of this piped stream
 		defer pools.BufioWriter32KPool.Put(ta.Buffer)
 
+		sort.Sort(changesByPath(changes))
+
 		// In general we log errors here but ignore them because
 		// during e.g. a diff operation the container can continue
 		// mutating the filesystem and we can see transient errors