inspect: Ignore character devices for IO limits

Cgroup block I/O limits cannot be applied to character devices.

Ignore character devices in the inspect output.

Update the API tests to use the null block device `/dev/nullb0` (if
available) instead of `/dev/zero` for testing I/O limits.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

libpod/container_inspect.go

@@ -653,7 +653,7 @@ func (c *Container) GetDevices(priv bool, ctrSpec spec.Spec, deviceNodes map[str
 		for _, dev := range ctrSpec.Linux.Devices {
 			key := fmt.Sprintf("%d:%d", dev.Major, dev.Minor)
 			if deviceNodes == nil {
-				nodes, err := util.FindDeviceNodes()
+				nodes, err := util.FindDeviceNodes(false)
 				if err != nil {
 					return nil, err
 				}
@@ -678,7 +678,7 @@ func blkioDeviceThrottle(deviceNodes map[string]string, devs []spec.LinuxThrottl
 	for _, dev := range devs {
 		key := fmt.Sprintf("%d:%d", dev.Major, dev.Minor)
 		if deviceNodes == nil {
-			nodes, err := util.FindDeviceNodes()
+			nodes, err := util.FindDeviceNodes(true)
 			if err != nil {
 				return nil, err
 			}

libpod/container_inspect_linux.go

@@ -89,7 +89,7 @@ func (c *Container) platformInspectContainerHostConfig(ctrSpec *spec.Spec, hostC
 						continue
 					}
 					if deviceNodes == nil {
-						nodes, err := util.FindDeviceNodes()
+						nodes, err := util.FindDeviceNodes(true)
 						if err != nil {
 							return err
 						}

pkg/util/utils_linux.go

@@ -33,7 +33,8 @@ func GetContainerPidInformationDescriptors() ([]string, error) {
 // [major:minor] is the device's major and minor numbers formatted as, for
 // example, 2:0 and path is the path to the device node.
 // Symlinks to nodes are ignored.
-func FindDeviceNodes() (map[string]string, error) {
+// If onlyBlockDevices is specified, character devices are ignored.
+func FindDeviceNodes(onlyBlockDevices bool) (map[string]string, error) {
 	nodes := make(map[string]string)
 	err := filepath.WalkDir("/dev", func(path string, d fs.DirEntry, err error) error {
 		if err != nil {
@@ -44,7 +45,13 @@ func FindDeviceNodes() (map[string]string, error) {
 		}
 
 		// If we aren't a device node, do nothing.
-		if d.Type()&(os.ModeDevice|os.ModeCharDevice) == 0 {
+		if d.Type()&os.ModeDevice == 0 {
+			return nil
+		}
+
+		// Ignore character devices, because it is not possible to set limits on them.
+		// os.ModeCharDevice is usable only when os.ModeDevice is set.
+		if onlyBlockDevices && d.Type()&os.ModeCharDevice != 0 {
 			return nil
 		}
 

pkg/util/utils_unsupported.go

@@ -5,6 +5,6 @@ package util
 import "errors"
 
 // FindDeviceNodes is not implemented anywhere except Linux.
-func FindDeviceNodes() (map[string]string, error) {
+func FindDeviceNodes(onlyBlockDevices bool) (map[string]string, error) {
 	return nil, errors.New("not supported on non-Linux OSes")
 }

test/apiv2/20-containers.at

@@ -710,15 +710,15 @@ t GET libpod/containers/$cname/json 200 \
   .ImageName=$IMAGE \
   .Name=$cname
 
-if root; then
+if root && test -e /dev/nullb0; then
   podman run -dt --name=updateCtr alpine
   echo '{
     "Memory":{"Limit":500000},
     "CPU":{"Shares":123},
-    "DeviceReadBPs": [{ "Path": "/dev/zero", "Rate": 10485760 }],
+    "DeviceReadBPs": [{ "Path": "/dev/nullb0", "Rate": 10485760 }],
-    "DeviceWriteBPs": [{ "Path": "/dev/zero", "Rate": 31457280 }],
+    "DeviceWriteBPs": [{ "Path": "/dev/nullb0", "Rate": 31457280 }],
-    "DeviceReadIOPs": [{ "Path": "/dev/zero", "Rate": 2000 }],
+    "DeviceReadIOPs": [{ "Path": "/dev/nullb0", "Rate": 2000 }],
-    "DeviceWriteIOPs": [{ "Path": "/dev/zero", "Rate": 4000 }]
+    "DeviceWriteIOPs": [{ "Path": "/dev/nullb0", "Rate": 4000 }]
     }' >${TMPD}/update.json
   t POST libpod/containers/updateCtr/update ${TMPD}/update.json 201
 
@@ -734,25 +734,25 @@ if root; then
 
   BlkioDeviceReadBps_expected='[
   {
-    "Path": "/dev/zero",
+    "Path": "/dev/nullb0",
     "Rate": 10485760
   }
 ]'
   BlkioDeviceWriteBPs_expected='[
   {
-    "Path": "/dev/zero",
+    "Path": "/dev/nullb0",
     "Rate": 31457280
   }
 ]'
   BlkioDeviceReadIOPs_expected='[
   {
-    "Path": "/dev/zero",
+    "Path": "/dev/nullb0",
     "Rate": 2000
   }
 ]'
   BlkioDeviceWriteIOPs_expected='[
   {
-    "Path": "/dev/zero",
+    "Path": "/dev/nullb0",
     "Rate": 4000
   }
 ]'