device: Do not rescan PCI bus

PCI bus rescan code was added long time ago in Clear Containers due to lack of
ACPI support in QEMU 2.9 + q35 [1]. Now this code is messing up PCIe hotplug
in Kata Containers. A workaround to this issue is the "lazy attach"
mechanism [2] that hotplugs LBS (Large BAR space) devices after re-scanning the
PCI bus, unfourtunately some non-LBS devices are being affected too, for
instance SR-IOV devices. It would not make sense to lazy-attach non-LBS
devices because kata will end up lazy-attaching all the devices, having said
that, the PCI bus rescan code and the "lazy attach" mechanism should be removed

fixes kata-containers#781
fixes kata-containers/runtime#2664

[1]: clearcontainers/agent#139
[2]: kata-containers/runtime#2461

Signed-off-by: Julio Montes <julio.montes@intel.com>

device.go

@@ -80,10 +80,6 @@ var deviceHandlerList = map[string]deviceHandler{
 	driverNvdimmType:  nvdimmDeviceHandler,
 }
 
-func rescanPciBus() error {
-	return ioutil.WriteFile(pciBusRescanFile, []byte{'1'}, pciBusMode)
-}
-
 // getDevicePCIAddress fetches the complete PCI address in sysfs, based on the PCI
 // identifier provided. This should be in the format: "bridgeAddr/deviceAddr".
 // Here, bridgeAddr is the address at which the brige is attached on the root bus,
@@ -178,14 +174,6 @@ func getPCIDeviceNameImpl(s *sandbox, pciID string) (string, error) {
 		return "", err
 	}
 
-	fieldLogger := agentLog.WithField("pciAddr", pciAddr)
-
-	// Rescan pci bus if we need to wait for a new pci device
-	if err = rescanPciBus(); err != nil {
-		fieldLogger.WithError(err).Error("Failed to scan pci bus")
-		return "", err
-	}
-
 	return getDeviceName(s, pciAddr)
 }
 

device_test.go

@@ -503,45 +503,6 @@ func TestUpdateSpecDeviceList(t *testing.T) {
 	assert.NoError(err)
 }
 
-func TestRescanPciBus(t *testing.T) {
-	skipUnlessRoot(t)
-
-	assert := assert.New(t)
-
-	err := rescanPciBus()
-	assert.Nil(err)
-
-}
-
-func TestRescanPciBusSubverted(t *testing.T) {
-	assert := assert.New(t)
-
-	dir, err := ioutil.TempDir("", "")
-	assert.NoError(err)
-	defer os.RemoveAll(dir)
-
-	rescanDir := filepath.Join(dir, "rescan-dir")
-
-	err = os.MkdirAll(rescanDir, testDirMode)
-	assert.NoError(err)
-
-	rescan := filepath.Join(rescanDir, "rescan")
-
-	savedFile := pciBusRescanFile
-	defer func() {
-		pciBusRescanFile = savedFile
-	}()
-
-	pciBusRescanFile = rescan
-
-	err = rescanPciBus()
-	assert.NoError(err)
-
-	os.RemoveAll(rescanDir)
-	err = rescanPciBus()
-	assert.Error(err)
-}
-
 func TestVirtioMmioBlkDeviceHandler(t *testing.T) {
 	assert := assert.New(t)
 
@@ -634,13 +595,6 @@ func TestGetPCIDeviceName(t *testing.T) {
 
 	_, err = getPCIDeviceNameImpl(&sb, "")
 	assert.Error(err)
-
-	rescanDir := filepath.Dir(pciBusRescanFile)
-	err = os.MkdirAll(rescanDir, testDirMode)
-	assert.NoError(err)
-
-	_, err = getPCIDeviceNameImpl(&sb, "")
-	assert.Error(err)
 }
 
 func TestGetSCSIDevPath(t *testing.T) {

grpc.go

@@ -611,12 +611,6 @@ func (a *agentGRPC) CreateContainer(ctx context.Context, req *pb.CreateContainer
 		return emptyResp, err
 	}
 
-	// re-scan PCI bus
-	// looking for hidden devices
-	if err = rescanPciBus(); err != nil {
-		agentLog.WithError(err).Warn("Could not rescan PCI bus")
-	}
-
 	// Some devices need some extra processing (the ones invoked with
 	// --device for instance), and that's what this call is doing. It
 	// updates the devices listed in the OCI spec, so that they actually