Added spec command to create OCI spec config.json

The spec command is analygous to the 'runc spec' command and allows for
the convenient creation of a config.json file for users that don't have
runc handy.

Change-Id: Ifdfec37e023048ea461c32da1a9042a45b37d856
PiperOrigin-RevId: 216907826

runsc/cmd/BUILD

@@ -23,6 +23,7 @@ go_library(
         "restore.go",
         "resume.go",
         "run.go",
+        "spec.go",
         "start.go",
         "state.go",
         "wait.go",

runsc/cmd/spec.go

@@ -0,0 +1,182 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cmd
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"context"
+	"flag"
+	"github.com/google/subcommands"
+)
+
+var specTemplate = []byte(`{
+	"ociVersion": "1.0.0",
+	"process": {
+		"terminal": true,
+		"user": {
+			"uid": 0,
+			"gid": 0
+		},
+		"args": [
+			"sh"
+		],
+		"env": [
+			"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
+			"TERM=xterm"
+		],
+		"cwd": "/",
+		"capabilities": {
+			"bounding": [
+				"CAP_AUDIT_WRITE",
+				"CAP_KILL",
+				"CAP_NET_BIND_SERVICE"
+			],
+			"effective": [
+				"CAP_AUDIT_WRITE",
+				"CAP_KILL",
+				"CAP_NET_BIND_SERVICE"
+			],
+			"inheritable": [
+				"CAP_AUDIT_WRITE",
+				"CAP_KILL",
+				"CAP_NET_BIND_SERVICE"
+			],
+			"permitted": [
+				"CAP_AUDIT_WRITE",
+				"CAP_KILL",
+				"CAP_NET_BIND_SERVICE"
+			],
+			"ambient": [
+				"CAP_AUDIT_WRITE",
+				"CAP_KILL",
+				"CAP_NET_BIND_SERVICE"
+			]
+		},
+		"rlimits": [
+			{
+				"type": "RLIMIT_NOFILE",
+				"hard": 1024,
+				"soft": 1024
+			}
+		]
+	},
+	"root": {
+		"path": "rootfs",
+		"readonly": true
+	},
+	"hostname": "runsc",
+	"mounts": [
+		{
+			"destination": "/proc",
+			"type": "proc",
+			"source": "proc"
+		},
+		{
+			"destination": "/dev",
+			"type": "tmpfs",
+			"source": "tmpfs",
+			"options": []
+		},
+		{
+			"destination": "/sys",
+			"type": "sysfs",
+			"source": "sysfs",
+			"options": [
+				"nosuid",
+				"noexec",
+				"nodev",
+				"ro"
+			]
+		}
+	],
+	"linux": {
+		"namespaces": [
+			{
+				"type": "pid"
+			},
+			{
+				"type": "network"
+			},
+			{
+				"type": "ipc"
+			},
+			{
+				"type": "uts"
+			},
+			{
+				"type": "mount"
+			}
+		]
+	}
+}`)
+
+// Spec implements subcommands.Command for the "spec" command.
+type Spec struct {
+	bundle string
+}
+
+// Name implements subcommands.Command.Name.
+func (*Spec) Name() string {
+	return "spec"
+}
+
+// Synopsis implements subcommands.Command.Synopsis.
+func (*Spec) Synopsis() string {
+	return "create a new OCI bundle specification file"
+}
+
+// Usage implements subcommands.Command.Usage.
+func (*Spec) Usage() string {
+	return `spec [options] - create a new OCI bundle specification file.
+
+The spec command creates a new specification file (config.json) for a new OCI bundle.
+
+The specification file is a starter file that runs the "sh" command in the container. You
+should edit the file to suit your needs. You can find out more about the format of the
+specification file by visiting the OCI runtime spec repository:
+https://github.com/opencontainers/runtime-spec/
+
+EXAMPLE:
+    $ mkdir -p bundle/rootfs
+    $ cd bundle
+    $ runsc spec
+    $ docker export $(docker create hello-world) | tar -xf - -C rootfs
+    $ sed -i 's;"sh";"/hello";' config.json
+    $ sudo runsc run hello
+
+`
+}
+
+// SetFlags implements subcommands.Command.SetFlags.
+func (s *Spec) SetFlags(f *flag.FlagSet) {
+	f.StringVar(&s.bundle, "bundle", ".", "path to the root of the OCI bundle")
+}
+
+// Execute implements subcommands.Command.Execute.
+func (s *Spec) Execute(_ context.Context, f *flag.FlagSet, args ...interface{}) subcommands.ExitStatus {
+	confPath := filepath.Join(s.bundle, "config.json")
+	if _, err := os.Stat(confPath); !os.IsNotExist(err) {
+		Fatalf("file %q already exists", confPath)
+	}
+
+	if err := ioutil.WriteFile(confPath, specTemplate, 0664); err != nil {
+		Fatalf("error writing to %q: %v", confPath, err)
+	}
+
+	return subcommands.ExitSuccess
+}

runsc/main.go

@@ -86,6 +86,7 @@ func main() {
 	subcommands.Register(new(cmd.Restore), "")
 	subcommands.Register(new(cmd.Resume), "")
 	subcommands.Register(new(cmd.Run), "")
+	subcommands.Register(new(cmd.Spec), "")
 	subcommands.Register(new(cmd.Start), "")
 	subcommands.Register(new(cmd.State), "")
 	subcommands.Register(new(cmd.Wait), "")