version: Add a version command

And adjust 'runc --version' to print exactly the same content.

The

  $ COMMAND --version

interface is a popular one for this information and makes a lot of
sense for single-action commands.  For example, printf(1) [1] is only
ever going to do one meaningful thing, so --version, --help, and other
command-like actions work well as options.

Umbrella commands with multiple sub-commands, on the other hand, have
a more consistent interface if '... and exit' actions get their own
sub-commands.  That allows you to declare an interface like:

  $ COMMAND [global-options] SUB-COMMAND [sub-command-specific-options] [sub-command-specific-arguments]

without having to say "except if you use a sub-command-like global
option, in which case SUB-COMMAND is not allowed".

With this commit, we add support for 'version' while keeping
--version, because while 'version' makes more sense for umbrella
commands, a user may not know if runc is an umbrella command when they
ask for the version.

Existing umbrella commands are not particularly consistent:

* git(1) supports both --version and 'version', --help and 'help'.
* btrfs(8) supports both --version and 'version', --help and 'help'.
* ip(1) supports -V / -Version and 'help'.
* npm supports 'version' and 'help'.
* pip supports '--version', --help and 'help'.

[1]: http://www.man7.org/linux/man-pages/man1/printf.1.html

Signed-off-by: W. Trevor King <[email protected]>

Author: wking

Makefile

@@ -25,10 +25,10 @@ MAN_INSTALL_PATH := ${PREFIX}/share/man/man8/
 VERSION := ${shell cat ./VERSION}
 
 all: $(RUNC_LINK)
-	go build -i -ldflags "-X main.gitCommit=${COMMIT} -X main.version=${VERSION}" -tags "$(BUILDTAGS)" -o runc .
+	go build -i -ldflags "-X version.gitCommit=${COMMIT} -X version.version=${VERSION}" -tags "$(BUILDTAGS)" -o runc .
 
 static: $(RUNC_LINK)
-	CGO_ENABLED=1 go build -i -tags "$(BUILDTAGS) cgo static_build" -ldflags "-w -extldflags -static -X main.gitCommit=${COMMIT} -X main.version=${VERSION}" -o runc .
+	CGO_ENABLED=1 go build -i -tags "$(BUILDTAGS) cgo static_build" -ldflags "-w -extldflags -static -X version.gitCommit=${COMMIT} -X version.version=${VERSION}" -o runc .
 
 $(RUNC_LINK):
 	ln -sfn $(CURDIR) $(RUNC_LINK)

main.go

@@ -3,21 +3,11 @@ package main
 import (
 	"fmt"
 	"os"
-	"strings"
 
 	"github.com/Sirupsen/logrus"
-	"github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/urfave/cli"
 )
 
-// version will be populated by the Makefile, read from
-// VERSION file of the source code.
-var version = ""
-
-// gitCommit will be the hash that the binary was built from
-// and will be populated by the Makefile
-var gitCommit = ""
-
 const (
 	specConfig = "config.json"
 	usage      = `Open Container Initiative runtime
@@ -50,15 +40,9 @@ func main() {
 	app.Name = "runc"
 	app.Usage = usage
 
-	var v []string
-	if version != "" {
-		v = append(v, version)
-	}
-	if gitCommit != "" {
-		v = append(v, fmt.Sprintf("commit: %s", gitCommit))
+	cli.VersionPrinter = func(context *cli.Context) {
+		printVersion(context)
 	}
-	v = append(v, fmt.Sprintf("spec: %s", specs.Version))
-	app.Version = strings.Join(v, "\n")
 	app.Flags = []cli.Flag{
 		cli.BoolFlag{
 			Name:  "debug",
@@ -107,6 +91,7 @@ func main() {
 		startCommand,
 		stateCommand,
 		updateCommand,
+		versionCommand,
 	}
 	app.Before = func(context *cli.Context) error {
 		if context.GlobalBool("debug") {

version.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/urfave/cli"
+)
+
+// version will be populated by the Makefile, read from
+// VERSION file of the source code.
+var version = ""
+
+// gitCommit will be the hash that the binary was built from
+// and will be populated by the Makefile
+var gitCommit = ""
+
+var versionCommand = cli.Command{
+	Name:        "version",
+	Usage:       "output the runtime version",
+	Description: `The version command outputs the runtime version.`,
+	Action:      printVersion,
+}
+
+func printVersion(context *cli.Context) (err error) {
+	if version == "" {
+		_, err = os.Stdout.WriteString("runC unknown\n")
+	} else {
+		_, err = os.Stdout.WriteString(fmt.Sprintf("runC %s\n", version))
+	}
+	if err != nil {
+		return err
+	}
+	if gitCommit != "" {
+		_, err = os.Stdout.WriteString(fmt.Sprintf("commit: %s\n", gitCommit))
+		if err != nil {
+			return err
+		}
+	}
+	_, err = os.Stdout.WriteString(fmt.Sprintf("spec: %s\n", specs.Version))
+	return err
+}