Ignore stats that are not available

Closes #13

Docker-DCO-1.1-Signed-off-by: Victor Marmol <vmarmol@google.com> (github: vmarmol)

cgroups/fs/blkio.go

@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"syscall"
 
 	"github.com/docker/libcontainer/cgroups"
 )
@@ -65,6 +66,9 @@ func getBlkioStat(path string) ([]cgroups.BlkioStatEntry, error) {
 	var blkioStats []cgroups.BlkioStatEntry
 	f, err := os.Open(path)
 	if err != nil {
+		if pathErr, ok := err.(*os.PathError); ok && pathErr.Err == syscall.ENOENT {
+			return blkioStats, nil
+		}
 		return nil, err
 	}
 	defer f.Close()

cgroups/fs/blkio_test.go

@@ -86,8 +86,8 @@ func TestBlkioStatsNoSectorsFile(t *testing.T) {
 
 	blkio := &blkioGroup{}
 	err := blkio.GetStats(helper.CgroupData, &actualStats)
-	if err == nil {
-		t.Fatal("Expected to fail, but did not")
+	if err != nil {
+		t.Fatalf("Failed unexpectedly: %s", err)
 	}
 }
 
@@ -102,8 +102,8 @@ func TestBlkioStatsNoServiceBytesFile(t *testing.T) {
 
 	blkio := &blkioGroup{}
 	err := blkio.GetStats(helper.CgroupData, &actualStats)
-	if err == nil {
-		t.Fatal("Expected to fail, but did not")
+	if err != nil {
+		t.Fatalf("Failed unexpectedly: %s", err)
 	}
 }
 
@@ -118,8 +118,8 @@ func TestBlkioStatsNoServicedFile(t *testing.T) {
 
 	blkio := &blkioGroup{}
 	err := blkio.GetStats(helper.CgroupData, &actualStats)
-	if err == nil {
-		t.Fatal("Expected to fail, but did not")
+	if err != nil {
+		t.Fatalf("Failed unexpectedly: %s", err)
 	}
 }
 
@@ -134,8 +134,8 @@ func TestBlkioStatsNoQueuedFile(t *testing.T) {
 
 	blkio := &blkioGroup{}
 	err := blkio.GetStats(helper.CgroupData, &actualStats)
-	if err == nil {
-		t.Fatal("Expected to fail, but did not")
+	if err != nil {
+		t.Fatalf("Failed unexpectedly: %s", err)
 	}
 }
 

cgroups/fs/memory.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"path/filepath"
 	"strconv"
+	"syscall"
 
 	"github.com/docker/libcontainer/cgroups"
 )
@@ -60,6 +61,9 @@ func (s *memoryGroup) GetStats(d *data, stats *cgroups.Stats) error {
 	// Set stats from memory.stat.
 	statsFile, err := os.Open(filepath.Join(path, "memory.stat"))
 	if err != nil {
+		if pathErr, ok := err.(*os.PathError); ok && pathErr.Err == syscall.ENOENT {
+			return nil
+		}
 		return err
 	}
 	defer statsFile.Close()

cgroups/fs/memory_test.go

@@ -43,8 +43,8 @@ func TestMemoryStatsNoStatFile(t *testing.T) {
 
 	memory := &memoryGroup{}
 	err := memory.GetStats(helper.CgroupData, &actualStats)
-	if err == nil {
-		t.Fatal("Expected failure")
+	if err != nil {
+		t.Fatal(err)
 	}
 }