avoid spawning thousands of process

when starting or creating containers in
environments which has thousands of
lines in /proc/mounts

https://work.aone.alibaba-inc.com/issue/22582695
Signed-off-by: shenling.yyb <[email protected]>

storage/quota/quota.go

@@ -3,6 +3,7 @@
 package quota
 
 import (
+	"context"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -341,11 +342,26 @@ func checkDevLimit(mountInfo *MountInfo, size uint64) error {
 }
 
 func getDevID(dir string) (uint64, error) {
-	// call "stat <dir>" to ensure stat not timeout
-	_, _, _, err := exec.Run(time.Second*5, "stat", dir)
-	if err != nil {
+	// ensure stat syscall don't timeout
+	idChan := make(chan uint64)
+	errChan := make(chan error)
+	timeoutChan := time.After(time.Second * 5)
+
+	go func() {
+		id, err := system.GetDevID(dir)
+		if err != nil {
+			errChan <- err
+			return
+		}
+		idChan <- id
+	}()
+
+	select {
+	case err := <-errChan:
 		return 0, err
+	case id := <-idChan:
+		return id, nil
+	case <-timeoutChan:
+		return 0, context.DeadlineExceeded
 	}
-
-	return system.GetDevID(dir)
 }

storage/quota/quota_test.go

@@ -0,0 +1,30 @@
+// +build linux
+
+package quota
+
+import (
+	"os"
+	"testing"
+
+	"github.com/alibaba/pouch/pkg/system"
+)
+
+func Test_getDevID(t *testing.T) {
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("get work directory error %v", err)
+	}
+	expectID, err := system.GetDevID(wd)
+	if err != nil {
+		t.Fatalf("get dev id error of %s: %v", wd, err)
+	}
+
+	gotID, err := getDevID(wd)
+	if err != nil {
+		t.Fatalf("get dev id error of %s by getDevID: %v", wd, err)
+	}
+
+	if expectID != gotID {
+		t.Fatalf("getDevID error expect %d got %d", expectID, gotID)
+	}
+}