Re-add Fedora 31 migration code.

In the process, make everything in the config omitempty in TOML.
We're seeing issues (notably [1]) where, after rewriting
libpod.conf, fields that were not previously populated are
written - and, because they were not previously written, they are
included as empty. This is unfortunately different from not
included at all - it means that we need to assume the user
explicitly unset the value, and we can't use defaults. Setting
omitempty prevents us from writing things that should not be
written as they were not set originally.

[1] https://github.com/containers/libpod/issues/4210

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

1 files changed, 60 insertions, 26 deletions

diff --git a/libpod/config/config.go b/libpod/config/config.go
index f1fa70fbc..0e867a50e 100644
--- a/libpod/config/config.go
+++ b/libpod/config/config.go
@@ -12,6 +12,7 @@ import (
 
 	"github.com/BurntSushi/toml"
 	"github.com/containers/libpod/libpod/define"
+	"github.com/containers/libpod/pkg/cgroups"
 	"github.com/containers/libpod/pkg/rootless"
 	"github.com/containers/libpod/pkg/util"
 	"github.com/containers/storage"
@@ -137,11 +138,11 @@ type Config struct {
 	// VolumePath is the default location that named volumes will be created
 	// under. This convention is followed by the default volume driver, but
 	// may not be by other drivers.
-	VolumePath string `toml:"volume_path"`
+	VolumePath string `toml:"volume_path,omitempty"`
 
 	// ImageDefaultTransport is the default transport method used to fetch
 	// images.
-	ImageDefaultTransport string `toml:"image_default_transport"`
+	ImageDefaultTransport string `toml:"image_default_transport,omitempty"`
 
 	// SignaturePolicyPath is the path to a signature policy to use for
 	// validating images. If left empty, the containers/image default signature
@@ -149,61 +150,61 @@ type Config struct {
 	SignaturePolicyPath string `toml:"signature_policy_path,omitempty"`
 
 	// OCIRuntime is the OCI runtime to use.
-	OCIRuntime string `toml:"runtime"`
+	OCIRuntime string `toml:"runtime,omitempty"`
 
 	// OCIRuntimes are the set of configured OCI runtimes (default is runc).
-	OCIRuntimes map[string][]string `toml:"runtimes"`
+	OCIRuntimes map[string][]string `toml:"runtimes,omitempty"`
 
 	// RuntimeSupportsJSON is the list of the OCI runtimes that support
 	// --format=json.
-	RuntimeSupportsJSON []string `toml:"runtime_supports_json"`
+	RuntimeSupportsJSON []string `toml:"runtime_supports_json,omitempty"`
 
 	// RuntimeSupportsNoCgroups is a list of OCI runtimes that support
 	// running containers without CGroups.
-	RuntimeSupportsNoCgroups []string `toml:"runtime_supports_nocgroups"`
+	RuntimeSupportsNoCgroups []string `toml:"runtime_supports_nocgroups,omitempty"`
 
 	// RuntimePath is the path to OCI runtime binary for launching containers.
 	// The first path pointing to a valid file will be used This is used only
 	// when there are no OCIRuntime/OCIRuntimes defined.  It is used only to be
 	// backward compatible with older versions of Podman.
-	RuntimePath []string `toml:"runtime_path"`
+	RuntimePath []string `toml:"runtime_path,omitempty"`
 
 	// ConmonPath is the path to the Conmon binary used for managing containers.
 	// The first path pointing to a valid file will be used.
-	ConmonPath []string `toml:"conmon_path"`
+	ConmonPath []string `toml:"conmon_path,omitempty"`
 
 	// ConmonEnvVars are environment variables to pass to the Conmon binary
 	// when it is launched.
-	ConmonEnvVars []string `toml:"conmon_env_vars"`
+	ConmonEnvVars []string `toml:"conmon_env_vars,omitempty"`
 
 	// CGroupManager is the CGroup Manager to use Valid values are "cgroupfs"
 	// and "systemd".
-	CgroupManager string `toml:"cgroup_manager"`
+	CgroupManager string `toml:"cgroup_manager,omitempty"`
 
 	// InitPath is the path to the container-init binary.
-	InitPath string `toml:"init_path"`
+	InitPath string `toml:"init_path,omitempty"`
 
 	// StaticDir is the path to a persistent directory to store container
 	// files.
-	StaticDir string `toml:"static_dir"`
+	StaticDir string `toml:"static_dir,omitempty"`
 
 	// TmpDir is the path to a temporary directory to store per-boot container
 	// files. Must be stored in a tmpfs.
-	TmpDir string `toml:"tmp_dir"`
+	TmpDir string `toml:"tmp_dir,omitempty"`
 
 	// MaxLogSize is the maximum size of container logfiles.
 	MaxLogSize int64 `toml:"max_log_size,omitempty"`
 
 	// NoPivotRoot sets whether to set no-pivot-root in the OCI runtime.
-	NoPivotRoot bool `toml:"no_pivot_root"`
+	NoPivotRoot bool `toml:"no_pivot_root,omitempty"`
 
 	// CNIConfigDir sets the directory where CNI configuration files are
 	// stored.
-	CNIConfigDir string `toml:"cni_config_dir"`
+	CNIConfigDir string `toml:"cni_config_dir,omitempty"`
 
 	// CNIPluginDir sets a number of directories where the CNI network
 	// plugins can be located.
-	CNIPluginDir []string `toml:"cni_plugin_dir"`
+	CNIPluginDir []string `toml:"cni_plugin_dir,omitempty"`
 
 	// CNIDefaultNetwork is the network name of the default CNI network
 	// to attach pods to.
@@ -213,7 +214,7 @@ type Config struct {
 	// configuration files. When the same filename is present in in
 	// multiple directories, the file in the directory listed last in
 	// this slice takes precedence.
-	HooksDir []string `toml:"hooks_dir"`
+	HooksDir []string `toml:"hooks_dir,omitempty"`
 
 	// DefaultMountsFile is the path to the default mounts file for testing
 	// purposes only.
@@ -229,10 +230,10 @@ type Config struct {
 
 	// InfraImage is the image a pod infra container will use to manage
 	// namespaces.
-	InfraImage string `toml:"infra_image"`
+	InfraImage string `toml:"infra_image,omitempty"`
 
 	// InfraCommand is the command run to start up a pod infra container.
-	InfraCommand string `toml:"infra_command"`
+	InfraCommand string `toml:"infra_command,omitempty"`
 
 	// EnablePortReservation determines whether libpod will reserve ports on the
 	// host when they are forwarded to containers. When enabled, when ports are
@@ -241,13 +242,13 @@ type Config struct {
 	// programs on the host. However, this can cause significant memory usage if
 	// a container has many ports forwarded to it. Disabling this can save
 	// memory.
-	EnablePortReservation bool `toml:"enable_port_reservation"`
+	EnablePortReservation bool `toml:"enable_port_reservation,omitempty"`
 
 	// EnableLabeling indicates whether libpod will support container labeling.
-	EnableLabeling bool `toml:"label"`
+	EnableLabeling bool `toml:"label,omitempty"`
 
 	// NetworkCmdPath is the path to the slirp4netns binary.
-	NetworkCmdPath string `toml:"network_cmd_path"`
+	NetworkCmdPath string `toml:"network_cmd_path,omitempty"`
 
 	// NumLocks is the number of locks to make available for containers and
 	// pods.
@@ -257,17 +258,21 @@ type Config struct {
 	LockType string `toml:"lock_type,omitempty"`
 
 	// EventsLogger determines where events should be logged.
-	EventsLogger string `toml:"events_logger"`
+	EventsLogger string `toml:"events_logger,omitempty"`
 
 	// EventsLogFilePath is where the events log is stored.
-	EventsLogFilePath string `toml:"events_logfile_path"`
+	EventsLogFilePath string `toml:"events_logfile_path,omitempty"`
 
 	//DetachKeys is the sequence of keys used to detach a container.
-	DetachKeys string `toml:"detach_keys"`
+	DetachKeys string `toml:"detach_keys,omitempty"`
 
 	// SDNotify tells Libpod to allow containers to notify the host systemd of
 	// readiness using the SD_NOTIFY mechanism.
-	SDNotify bool
+	SDNotify bool `toml:",omitempty"`
+
+	// CgroupCheck indicates the configuration has been rewritten after an
+	// upgrade to Fedora 31 to change the default OCI runtime for cgroupsv2.
+	CgroupCheck bool `toml:"cgroup_check,omitempty"`
 }
 
 // DBConfig is a set of Libpod runtime configuration settings that are saved in
@@ -443,6 +448,9 @@ func NewConfig(userConfigPath string) (*Config, error) {
 		if err != nil {
 			return nil, errors.Wrapf(err, "error reading user config %q", userConfigPath)
 		}
+		if err := cgroupV2Check(userConfigPath, config); err != nil {
+			return nil, errors.Wrapf(err, "error rewriting configuration file %s", userConfigPath)
+		}
 	}
 
 	// Now, check if the user can access system configs and merge them if needed.
@@ -550,3 +558,29 @@ func (c *Config) checkCgroupsAndLogger() {
 		c.EventsLogger = "file"
 	}
 }
+
+// Since runc does not currently support cgroupV2
+// Change to default crun on first running of libpod.conf
+// TODO Once runc has support for cgroups, this function should be removed.
+func cgroupV2Check(configPath string, tmpConfig *Config) error {
+	if !tmpConfig.CgroupCheck && rootless.IsRootless() {
+		cgroupsV2, err := cgroups.IsCgroup2UnifiedMode()
+		if err != nil {
+			return err
+		}
+		if cgroupsV2 {
+			path, err := exec.LookPath("crun")
+			if err != nil {
+				logrus.Warnf("Can not find crun package on the host, containers might fail to run on cgroup V2 systems without crun: %q", err)
+				// Can't find crun path so do nothing
+				return nil
+			}
+			tmpConfig.CgroupCheck = true
+			tmpConfig.OCIRuntime = path
+			if err := tmpConfig.Write(configPath); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}