First step in fixing genuinetools#334

reexec.Init() wasn't called in img's main, while buildkit solver
enventually reexec'd in the registered initialization function
"docker-untar"

This is a quick-and-dirty fix to prevent an unecessary namespace unshare

internal/unshare/unshare.c

@@ -503,3 +503,20 @@ void nsexec(void)
 	/* Should never be reached. */
 	bail("should never be reached");
 }
+
+
+/*
+ * FIXME(lel-amri): This is a quick-and-dirty fix
+ * up to "End of the quick-and-dirty fix #1".
+ */
+int is_careless_reexec(int argc, char** argv)
+{
+	if (argc < 1)
+		return 1;
+	if (!strncmp(argv[0], "docker-untar", 13))
+		return 1;
+	return 0;
+}
+/*
+ * End of the quick-and-dirty fix #1
+ */

internal/unshare/unshare.go

@@ -3,8 +3,10 @@ package unshare
 /*
 #cgo CFLAGS: -Wall
 extern void nsexec();
-void __attribute__((constructor)) init(void) {
-	nsexec();
+extern int is_careless_reexec(int, char**);
+void __attribute__((constructor)) init(int argc, char** argv) {
+	if (!is_careless_reexec(argc, argv))
+		nsexec();
 }
 */
 import "C"

main.go

@@ -12,6 +12,7 @@ import (
 	"github.com/genuinetools/img/version"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
+	dockerreexec "github.com/docker/docker/pkg/reexec"
 )
 
 const (
@@ -50,6 +51,10 @@ Use "{{.CommandPath}} [command] --help" for more information about a command.{{e
 `
 
 func main() {
+	if dockerreexec.Init() {
+		return
+	}
+
 	var printVersionAndExit bool
 
 	cmd := &cobra.Command{