core/runtime: Check shim PluginInfo to enforce idmap support

This commit gets rid of the TODO by moving the check to use the
pluginInfo() infrastructure.

The check is only enforced for shims that return info that can be read
as type runtime.Features. For shims that don't provide that, we just
ignore it, as those shims might not be affected by this.

Signed-off-by: Rodrigo Campos <rodrigoca@microsoft.com>

cmd/containerd-shim-runc-v2/process/utils.go

@@ -21,7 +21,6 @@ package process
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -32,7 +31,6 @@ import (
 
 	"github.com/containerd/errdefs"
 	runc "github.com/containerd/go-runc"
-	specs "github.com/opencontainers/runtime-spec/specs-go"
 	"golang.org/x/sys/unix"
 )
 
@@ -41,8 +39,6 @@ const (
 	RuncRoot = "/run/containerd/runc"
 	// InitPidFile name of the file that contains the init pid
 	InitPidFile = "init.pid"
-	// configFile is the name of the runc config file
-	configFile = "config.json"
 )
 
 // safePid is a thread safe wrapper for pid.
@@ -188,23 +184,3 @@ func stateName(v interface{}) string {
 	}
 	panic(fmt.Errorf("invalid state %v", v))
 }
-
-func readConfig(path string) (spec *specs.Spec, err error) {
-	cfg := filepath.Join(path, configFile)
-	f, err := os.Open(cfg)
-	if err != nil {
-		if os.IsNotExist(err) {
-			return nil, fmt.Errorf("JSON specification file %s not found", cfg)
-		}
-		return nil, err
-	}
-	defer f.Close()
-
-	if err = json.NewDecoder(f).Decode(&spec); err != nil {
-		return nil, fmt.Errorf("failed to parse config: %w", err)
-	}
-	if spec == nil {
-		return nil, errors.New("config cannot be null")
-	}
-	return spec, nil
-}