Display version flag

.dockerignore

@@ -1,4 +1,3 @@
-.git
 Dockerfile
 README.md
 docker-bake.hcl

Dockerfile

@@ -90,9 +90,13 @@ FROM --platform=$BUILDPLATFORM golang:1.15-alpine AS binfmt
 COPY --from=xgo / /
 ENV CGO_ENABLED=0
 ARG TARGETPLATFORM
+ARG QEMU_VERSION
 WORKDIR /src
+RUN apk add --no-cache git
 RUN --mount=target=. \
-  TARGETPLATFORM=$TARGETPLATFORM go build -o /go/bin/binfmt ./cmd/binfmt
+  TARGETPLATFORM=$TARGETPLATFORM go build \
+    -ldflags "-X main.revision=$(git rev-parse --short HEAD) -X main.qemuVersion=${QEMU_VERSION}" \
+    -o /go/bin/binfmt ./cmd/binfmt
 
 FROM scratch AS binaries
 ARG BINARY_PREFIX

README.md

@@ -67,6 +67,15 @@ You can also uninstall all archs for a specific emulator:
 docker run --privileged --rm tonistiigi/binfmt --uninstall qemu-*
 ```
 
+## Display version
+
+```bash
+docker run --privileged --rm tonistiigi/binfmt --version
+```
+```
+binfmt/9a44d27 qemu/v6.0.0 go/1.15.11
+```
+
 ## Development commands
 
 ```bash

cmd/binfmt/main.go

@@ -8,6 +8,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"syscall"
 
@@ -20,12 +21,14 @@ var (
 	mount       string
 	toInstall   string
 	toUninstall string
+	flVersion   bool
 )
 
 func init() {
 	flag.StringVar(&mount, "mount", "/proc/sys/fs/binfmt_misc", "binfmt_misc mount point")
 	flag.StringVar(&toInstall, "install", "", "architectures to install")
 	flag.StringVar(&toUninstall, "uninstall", "", "architectures to uninstall")
+	flag.BoolVar(&flVersion, "version", false, "display version")
 }
 
 func uninstall(arch string) error {
@@ -155,14 +158,19 @@ func parseUninstall(in string) (out []string) {
 }
 
 func main() {
+	log.SetFlags(0) // no timestamps in logs
 	flag.Parse()
-
 	if err := run(); err != nil {
 		log.Printf("error: %+v", err)
 	}
 }
 
 func run() error {
+	if flVersion {
+		log.Printf("binfmt/%s qemu/%s go/%s", revision, qemuVersion, runtime.Version()[2:])
+		return nil
+	}
+
 	if _, err := os.Stat(filepath.Join(mount, "status")); err != nil {
 		if err := syscall.Mount("binfmt_misc", mount, "binfmt_misc", 0, ""); err != nil {
 			return errors.Wrapf(err, "cannot mount binfmt_misc filesystem at %s", mount)

cmd/binfmt/version.go

@@ -0,0 +1,6 @@
+package main
+
+var (
+	revision    = "unknown"
+	qemuVersion = "unknown"
+)