refactor: improve installation reliability

This change aims to make installations more unified and reliable. It
introduces the concept of a mountpoint manager that is capable of
mounting, unmounting, and moving a set of mountpoints in the correct
order.

Signed-off-by: Andrew Rynhard <andrew@andrewrynhard.com>

internal/pkg/installer/bootloader/syslinux/syslinux.go

@@ -0,0 +1,170 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package syslinux
+
+import (
+	"bytes"
+	"io/ioutil"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"text/template"
+
+	"github.com/pkg/errors"
+)
+
+const syslinuxCfgTpl = `DEFAULT {{ .Default }}
+  SAY Talos
+{{- range .Labels }}
+INCLUDE /{{ .Root }}/include.cfg
+{{- end }}`
+
+const syslinuxLabelTpl = `LABEL {{ .Root }}
+  KERNEL {{ .Kernel }}
+  INITRD {{ .Initrd }}
+  APPEND {{ .Append }}
+`
+
+const (
+	gptmbrbin   = "/usr/lib/syslinux/gptmbr.bin"
+	syslinuxefi = "/usr/lib/syslinux/syslinux.efi"
+	ldlinuxe64  = "/usr/lib/syslinux/ldlinux.e64"
+)
+
+// Cfg reprsents the syslinux.cfg file.
+type Cfg struct {
+	Default string
+	Labels  []*Label
+}
+
+// Label reprsents a label in the syslinux.cfg file.
+type Label struct {
+	Root   string
+	Kernel string
+	Initrd string
+	Append string
+}
+
+// Syslinux represents the syslinux bootloader.
+type Syslinux struct{}
+
+// Prepare implements the Bootloader interface. It works by writing
+// gptmbr.bin to a block device.
+func Prepare(dev string) (err error) {
+	b, err := ioutil.ReadFile(gptmbrbin)
+	if err != nil {
+		return err
+	}
+	f, err := os.OpenFile(dev, os.O_WRONLY, os.ModeDevice)
+	if err != nil {
+		return err
+	}
+	// nolint: errcheck
+	defer f.Close()
+	if _, err := f.Write(b); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Install implements the Bootloader interface. It sets up syslinux with the
+// specified kernel parameters.
+func Install(base string, config interface{}) (err error) {
+	syslinuxcfg, ok := config.(*Cfg)
+	if !ok {
+		return errors.New("expected a syslinux config")
+	}
+
+	efiDir := filepath.Join(base, "EFI", "BOOT")
+	if err = os.MkdirAll(efiDir, 0700); err != nil {
+		return err
+	}
+
+	input, err := ioutil.ReadFile(syslinuxefi)
+	if err != nil {
+		return err
+	}
+
+	err = ioutil.WriteFile(efiDir+"/BOOTX64.EFI", input, 0600)
+	if err != nil {
+		return err
+	}
+
+	input, err = ioutil.ReadFile(ldlinuxe64)
+	if err != nil {
+		return err
+	}
+
+	err = ioutil.WriteFile(efiDir+"/ldlinux.e64", input, 0600)
+	if err != nil {
+		return err
+	}
+
+	paths := []string{filepath.Join(base, "syslinux", "syslinux.cfg"), filepath.Join(base, "EFI", "syslinux", "syslinux.cfg")}
+	for _, path := range paths {
+		if err = WriteSyslinuxCfg(base, path, syslinuxcfg); err != nil {
+			return err
+		}
+	}
+
+	if err = cmd("extlinux", "--install", filepath.Dir(paths[0])); err != nil {
+		return errors.Wrap(err, "failed to install extlinux")
+	}
+
+	return nil
+}
+
+// WriteSyslinuxCfg write syslinux.cfg to disk.
+func WriteSyslinuxCfg(base, path string, syslinuxcfg *Cfg) (err error) {
+	b := []byte{}
+	wr := bytes.NewBuffer(b)
+	t := template.Must(template.New("syslinux").Parse(syslinuxCfgTpl))
+	if err = t.Execute(wr, syslinuxcfg); err != nil {
+		return err
+	}
+
+	dir := filepath.Dir(path)
+	if err = os.MkdirAll(dir, os.ModeDir); err != nil {
+		return err
+	}
+
+	log.Println("writing syslinux.cfg to disk")
+	if err = ioutil.WriteFile(path, wr.Bytes(), 0600); err != nil {
+		return err
+	}
+
+	for _, label := range syslinuxcfg.Labels {
+		b = []byte{}
+		wr = bytes.NewBuffer(b)
+		t = template.Must(template.New("syslinux").Parse(syslinuxLabelTpl))
+		if err = t.Execute(wr, label); err != nil {
+			return err
+		}
+
+		dir = filepath.Join(base, label.Root)
+		if err = os.MkdirAll(dir, os.ModeDir); err != nil {
+			return err
+		}
+
+		log.Printf("writing syslinux label %s to disk", label.Root)
+		if err = ioutil.WriteFile(filepath.Join(dir, "include.cfg"), wr.Bytes(), 0600); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func cmd(name string, args ...string) error {
+	cmd := exec.Command(name, args...)
+	err := cmd.Start()
+	if err != nil {
+		return err
+	}
+
+	return cmd.Wait()
+}