Add support for pkg/reexec on FreeBSD

Signed-off-by: Doug Rabson <dfr@rabson.org>

pkg/reexec/command_freebsd.go

@@ -0,0 +1,37 @@
+// +build freebsd
+
+package reexec
+
+import (
+	"context"
+	"os"
+	"os/exec"
+
+	"golang.org/x/sys/unix"
+)
+
+// Self returns the path to the current process's binary.
+// Uses sysctl.
+func Self() string {
+	path, err := unix.SysctlArgs("kern.proc.pathname", -1)
+	if err == nil {
+		return path
+	}
+	return os.Args[0]
+}
+
+// Command returns *exec.Cmd which has Path as current binary.
+// For example if current binary is "docker" at "/usr/bin/", then cmd.Path will
+// be set to "/usr/bin/docker".
+func Command(args ...string) *exec.Cmd {
+	cmd := exec.Command(Self())
+	cmd.Args = args
+	return cmd
+}
+
+// CommandContext returns *exec.Cmd which has Path as current binary.
+func CommandContext(ctx context.Context, args ...string) *exec.Cmd {
+	cmd := exec.CommandContext(ctx, Self())
+	cmd.Args = args
+	return cmd
+}

pkg/reexec/command_unix.go

@@ -1,4 +1,5 @@
-// +build freebsd solaris darwin
+//go:build solaris || darwin
+// +build solaris darwin
 
 package reexec