Merge pull request #10 from sarus-suite/efficient-mirror

Mirror mechanism that enables parallelFS of store has been upgraded to avoid copying the squash directory. With this upgrade, only the store metadata used by the containers/storage library are mirrored into local storage, while the squash data is kept in parallelFS with mirror access via symlink.
This approach avoids the copy of the squash images, saving local space and large data transfers.

Author: fcruzcscs

cmd/migration.go

@@ -331,9 +331,6 @@ func createSquashSidecarFromMount(srcDir, link string, cfg common.Config) error
 
 	squashPath := filepath.Join(cfg.RoStoragePath, "squash", link+".squash")
 	if _, err := os.Stat(squashPath); errors.Is(err, os.ErrNotExist) {
-		if err := os.MkdirAll(filepath.Dir(squashPath), 0o755); err != nil {
-			return err
-		}
 
 		// Choose default or user provided flags
 		defaultFlags := []string {

common/rsync-mirror.go

@@ -5,6 +5,8 @@ import (
     "os"
     "os/exec"
     "path/filepath"
+
+	log "github.com/sirupsen/logrus"
 )
 
 // Mirror creates a writable mirror of srcDir in a temp directory.
@@ -13,23 +15,55 @@ import (
 //
 // Note: this requires the "rsync" binary to be installed and in PATH.
 func Mirror(srcDir string) (mirrorDir string, cleanup func() error, err error) {
+	log.Infof("Mirror: creating temp dir for %q", srcDir)
+
     mp, err := os.MkdirTemp("", "rsync-mirror-")
     if err != nil {
-        return "", nil, fmt.Errorf("failed to create temp dir: %w", err)
+        return "", nil, fmt.Errorf("Failed to create temp dir: %w", err)
     }
 
-    // Ensure the srcDir path ends with a trailing slash for rsync behavior
+
     srcPath := filepath.Clean(srcDir) + string(os.PathSeparator)
     mirrorPath := filepath.Clean(mp) + string(os.PathSeparator)
+    log.Infof("Mirror: rsync from %s to %s (no squash/)", srcPath, mirrorPath)
 
-    cmd := exec.Command("rsync", "-a", srcPath, mirrorPath)
+    // Setup mirror but skip squash/ dir
+    cmd := exec.Command("rsync",
+        "-a",
+        "--exclude=squash/",
+        srcPath, mirrorPath,
+    )
     if out, err2 := cmd.CombinedOutput(); err2 != nil {
         os.RemoveAll(mp)
-        return "", nil, fmt.Errorf("initial rsync failed: %v\n%s", err2, out)
+        return "", nil, fmt.Errorf("Initial rsync failed: %v\n%s", err2, out)
     }
 
+    // In case srcDir is not init, we might not have a squash dir, lets create it
+    realSquash := filepath.Join(srcDir, "squash")
+    linkName   := filepath.Join(mirrorPath, "squash")
+    log.Infof("Mirror: creating squash symlink %s to %s", linkName, realSquash)
+    if err := os.MkdirAll(realSquash, 0o755); err != nil {
+        return "", nil, fmt.Errorf("Failed to create real squash dir %q: %w", realSquash, err)
+    }
+    if err2 := os.Symlink(realSquash, linkName); err2 != nil {
+        os.RemoveAll(mp)
+        return "", nil, fmt.Errorf("Squash symlink failed: %w", err2)
+    }
+
+    // On cleanup we remove link then rsync back
     cleanup = func() error {
-        cmdBack := exec.Command("rsync", "-a", "--delete", mirrorPath, srcPath)
+        log.Infof("Mirror-cleanup: remove mirror’s squash symlink")
+        if err := os.Remove(filepath.Join(mirrorPath, "squash")); err != nil {
+            return fmt.Errorf("Failed to remove squash symlink: %w", err)
+        }
+
+        log.Infof("Mirror-cleanup: rsync back from %s to %s (excluding squash/)", mirrorPath, srcPath)
+        cmdBack := exec.Command("rsync",
+            "-a",
+            "--exclude=squash/",
+            "--delete",
+            mirrorPath, srcPath,
+        )
         if out, err2 := cmdBack.CombinedOutput(); err2 != nil {
             return fmt.Errorf("rsync back failed: %v\n%s", err2, out)
         }