drivers: Correct isPCIeDevice logic

Currently, isPCIeDevice() attempts to determine if a (host) device is
PCI-Express capable by looking up its link speed via the PCI slots
information in sysfs.  This is a) complicated and b) wrong.  PCI-e
devices don't have to have slots information, so this frequently fails.

Instead determine if devices are PCI-e by checking for the presence of
PCIe extended configuration space by looking at the size of the "config"
file in sysfs.

Forward ported from 6bf93b23 in the Kata 1.x runtime repository.

Fixes: #611

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

src/runtime/virtcontainers/device/config/config.go

@@ -89,9 +89,6 @@ var SysIOMMUPath = "/sys/kernel/iommu_groups"
 // SysBusPciDevicesPath is static string of /sys/bus/pci/devices
 var SysBusPciDevicesPath = "/sys/bus/pci/devices"
 
-// SysBusPciSlotsPath is static string of /sys/bus/pci/slots
-var SysBusPciSlotsPath = "/sys/bus/pci/slots"
-
 var getSysDevPath = getSysDevPathImpl
 
 // DeviceInfo is an embedded type that contains device data common to all types of devices.

src/runtime/virtcontainers/device/drivers/utils.go

@@ -9,6 +9,7 @@ package drivers
 import (
 	"fmt"
 	"io/ioutil"
+	"os"
 	"path/filepath"
 	"strings"
 
@@ -22,6 +23,8 @@ const (
 
 	PCIDomain   = "0000"
 	PCIeKeyword = "PCIe"
+
+	PCIConfigSpaceSize = 256
 )
 
 type PCISysFsType string
@@ -52,23 +55,17 @@ func isPCIeDevice(bdf string) bool {
 	if len(strings.Split(bdf, ":")) == 2 {
 		bdf = PCIDomain + ":" + bdf
 	}
-	slots, err := ioutil.ReadDir(config.SysBusPciSlotsPath)
+
+	configPath := filepath.Join(config.SysBusPciDevicesPath, bdf, "config")
+	fi, err := os.Stat(configPath)
 	if err != nil {
-		deviceLogger().WithError(err).WithField("path", config.SysBusPciSlotsPath).Warn("failed to list pci slots")
-		return false
-	}
-	b := strings.Split(bdf, ".")[0]
-	for _, slot := range slots {
-		address := getPCISlotProperty(slot.Name(), PCISysFsSlotsAddress)
-		if b == address {
-			maxBusSpeed := getPCISlotProperty(slot.Name(), PCISysFsSlotsMaxBusSpeed)
-			if strings.Contains(maxBusSpeed, PCIeKeyword) {
-				return true
-			}
-		}
+		deviceLogger().WithField("dev-bdf", bdf).WithField("error", err).Warning("Couldn't stat() configuration space file")
+		return false //Who knows?
 	}
-	deviceLogger().WithField("dev-bdf", bdf).Debug("can not find slot for bdf of pci device")
-	return false
+
+	// Plain PCI devices hav 256 bytes of configuration space,
+	// PCI-Express devices have 4096 bytes
+	return fi.Size() > PCIConfigSpaceSize
 }
 
 // read from /sys/bus/pci/devices/xxx/property
@@ -85,17 +82,6 @@ func getPCIDeviceProperty(bdf string, property PCISysFsProperty) string {
 	return rlt
 }
 
-// read from /sys/bus/pci/slots/xxx/property
-func getPCISlotProperty(slot string, property PCISysFsProperty) string {
-	propertyPath := filepath.Join(config.SysBusPciSlotsPath, slot, string(property))
-	rlt, err := readPCIProperty(propertyPath)
-	if err != nil {
-		deviceLogger().WithError(err).WithField("path", propertyPath).Warn("failed to read pci slot property")
-		return ""
-	}
-	return rlt
-}
-
 func readPCIProperty(propertyPath string) (string, error) {
 	var (
 		buf []byte