From 6bf93b23159e3f8eab62e9c2fc26ed9946a818e9 Mon Sep 17 00:00:00 2001
From: David Gibson <david@gibson.dropbear.id.au>
Date: Wed, 19 Aug 2020 16:06:22 +1000
Subject: [PATCH] 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.

Fixes: #2678

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 virtcontainers/device/config/config.go |  3 --
 virtcontainers/device/drivers/utils.go | 38 ++++++++------------------
 2 files changed, 12 insertions(+), 29 deletions(-)

diff --git a/virtcontainers/device/config/config.go b/virtcontainers/device/config/config.go
index 5f73cf7d8c..6146e8885d 100644
--- a/virtcontainers/device/config/config.go
+++ b/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.
diff --git a/virtcontainers/device/drivers/utils.go b/virtcontainers/device/drivers/utils.go
index ad046ca10b..72e27a5e21 100644
--- a/virtcontainers/device/drivers/utils.go
+++ b/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