issue 1841/S16: kernel_boot answers the loader, entries, kernels, booted entry and the fallback

ADR 0508 §9: the operator sees whether every boot menu lists the fallback kernel, and the room left on /boot.
2026-10-22 14:28:23 +02:00
parent e4373768af
commit bc77afa6bb
5 changed files with 214 additions and 5 deletions
@@ -0,0 +1,89 @@
+package main
+
+// kernel_boot: which loader booted the machine, its entries, the kernels in /boot, the entry it booted and
+// whether the fallback kernel is on the menu (novox/hq ADR 0508 §9, issue 1841). Reads only.
+
+import (
+	"os"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"strings"
+	"syscall"
+	"unicode/utf16"
+)
+
+const loaderSelected = "sys/firmware/efi/efivars/LoaderEntrySelected-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f"
+
+// BootState is what kernel_boot answers.
+type BootState struct {
+	Loader          string   `json:"loader"`
+	Entries         []string `json:"entries"`
+	Kernels         []string `json:"kernels"`
+	Booted          string   `json:"booted"`
+	FallbackPresent bool     `json:"fallback_present"`
+	BootFreeKiB     int64    `json:"boot_free_kib"`
+}
+
+var grubKernel = regexp.MustCompile(`(?m)^\s*linux\s+(?:/boot)?/(vmlinuz-\S+)`)
+var grubTitle = regexp.MustCompile(`(?m)^\s*menuentry\s+'([^']*)'`)
+var bootImage = regexp.MustCompile(`BOOT_IMAGE=(?:/boot)?/?(\S+)`)
+
+// Boot reads the machine, the loader the way the boot-entries script does: the loader's EFI variable means
+// systemd-boot, a grub.cfg without it GRUB.
+func (m *Machine) Boot() (*BootState, error) {
+	b := &BootState{Loader: "none", Entries: []string{}, Kernels: []string{}}
+	files, _ := filepath.Glob(m.path("boot/vmlinuz-*"))
+	for _, f := range files {
+		b.Kernels = append(b.Kernels, filepath.Base(f))
+	}
+	sort.Strings(b.Kernels)
+	hasKernel := func(name string) bool {
+		for _, k := range b.Kernels {
+			if k == name {
+				return true
+			}
+		}
+		return false
+	}
+	var s syscall.Statfs_t
+	if err := syscall.Statfs(m.path("boot"), &s); err == nil {
+		b.BootFreeKiB = int64(s.Bavail) * int64(s.Bsize) / 1024
+	}
+	if raw, err := os.ReadFile(m.path(loaderSelected)); err == nil {
+		b.Loader = "systemd-boot"
+		if len(raw) > 4 {
+			var u []uint16
+			for i := 4; i+1 < len(raw); i += 2 {
+				u = append(u, uint16(raw[i])|uint16(raw[i+1])<<8)
+			}
+			b.Booted = strings.TrimRight(string(utf16.Decode(u)), "\x00")
+		}
+		files, _ := filepath.Glob(m.path("boot/loader/entries/*.conf"))
+		for _, f := range files {
+			b.Entries = append(b.Entries, filepath.Base(f))
+		}
+		sort.Strings(b.Entries)
+		if raw, err := os.ReadFile(m.path("boot/loader/entries/mesh-linux-lts.conf")); err == nil {
+			b.FallbackPresent = strings.Contains(string(raw), "/vmlinuz-linux-lts") && hasKernel("vmlinuz-linux-lts")
+		}
+		return b, nil
+	}
+	if raw, err := os.ReadFile(m.path("boot/grub/grub.cfg")); err == nil {
+		b.Loader = "grub"
+		for _, t := range grubTitle.FindAllStringSubmatch(string(raw), -1) {
+			b.Entries = append(b.Entries, t[1])
+		}
+		for _, k := range grubKernel.FindAllStringSubmatch(string(raw), -1) {
+			if k[1] == "vmlinuz-linux-lts" && hasKernel("vmlinuz-linux-lts") {
+				b.FallbackPresent = true
+			}
+		}
+		if cmd, err := m.read("proc/cmdline"); err == nil {
+			if i := bootImage.FindStringSubmatch(cmd); i != nil {
+				b.Booted = i[1]
+			}
+		}
+	}
+	return b, nil
+}