Mount the filesystems we need so this can run as PID 1

fb.go

@@ -17,6 +17,7 @@ const (
 	kdText      = 0x00
 	kdGraphics  = 0x01
 	consolePath = "/dev/tty0"
+	fbPath      = "/dev/fb0"
 )
 
 // The variable screen info is a flat run of 40 u32s, so it is read as an array

init.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/unix"
+)
+
+// Running as PID 1 there is nothing underneath us: sysfs and devtmpfs are what
+// every check, counter and device node below is reached through, and no one
+// else is going to mount them. Written as checks like everything else, so this
+// is a silent no-op under a running system.
+
+type mountSpec struct {
+	dir    string
+	fstype string
+	magic  int64
+	flags  uintptr
+}
+
+var wantMounts = []mountSpec{
+	{"/proc", "proc", unix.PROC_SUPER_MAGIC, unix.MS_NOSUID | unix.MS_NODEV | unix.MS_NOEXEC},
+	{"/sys", "sysfs", unix.SYSFS_MAGIC, unix.MS_NOSUID | unix.MS_NODEV | unix.MS_NOEXEC},
+	// devtmpfs reports itself as tmpfs, so an existing tmpfs on /dev is taken
+	// as good enough; the kernel populates the nodes either way.
+	{"/dev", "devtmpfs", unix.TMPFS_MAGIC, unix.MS_NOSUID},
+}
+
+func checkMount(m mountSpec) checkResult {
+	res := checkResult{item: "mount " + m.dir}
+	var st unix.Statfs_t
+	err := unix.Statfs(m.dir, &st)
+	if err == unix.ENOENT {
+		if err := unix.Mkdir(m.dir, 0o755); err != nil {
+			res.err = fmt.Errorf("creating %s: %w", m.dir, err)
+			res.fatal = true
+			return res
+		}
+		err = unix.Statfs(m.dir, &st)
+	}
+	if err != nil {
+		res.err = err
+		res.fatal = true
+		return res
+	}
+	if int64(st.Type) == m.magic {
+		res.state = m.fstype + " already mounted"
+		return res
+	}
+	if err := unix.Mount(m.fstype, m.dir, m.fstype, m.flags, ""); err != nil {
+		res.err = err
+		res.fatal = true
+		return res
+	}
+	res.fixed = true
+	res.state = "mounted " + m.fstype
+	return res
+}
+
+// Each mount is what the next check stands on, so the first failure ends it.
+func mountFilesystems() []checkResult {
+	var out []checkResult
+	for _, m := range wantMounts {
+		res := checkMount(m)
+		out = append(out, res)
+		if res.fatal {
+			return out
+		}
+	}
+	return out
+}

main.go

@@ -637,10 +637,11 @@ func main() {
 	)
 	flag.Parse()
 
+	// Nothing here is recoverable by the time it reaches this point, and as PID 1
+	// a plain exit would panic the kernel anyway with less to show for it.
 	if err := run(*aName, *bName, *sizesArg,
 		*streams, *batch, *nsPerM); err != nil {
-		fmt.Fprintln(os.Stderr, "error:", err)
-		os.Exit(1)
+		panic(err)
 	}
 }
 
@@ -665,6 +666,11 @@ func run(aName, bName, sizesArg string,
 	if err != nil {
 		return err
 	}
+
+	if err := reportChecks("MOUNTS", mountFilesystems()); err != nil {
+		return err
+	}
+
 	a, err := lookupEndpoint(aName)
 	if err != nil {
 		return err
@@ -692,19 +698,8 @@ func run(aName, bName, sizesArg string,
 		ethertypes[i] = uint16(etherBase + i)
 	}
 
-	var fatal []string
-	var tuneRows [][]string
-	for _, r := range configureSystem(ifnames, ethertypes) {
-		tuneRows = append(tuneRows, []string{r.item, r.status(), r.detail()})
-		if r.fatal {
-			fatal = append(fatal, r.item)
-		}
-	}
-	fmt.Println(renderBox("HOST SETTINGS",
-		[]string{"CHECK", "STATUS", "DETAIL"},
-		[]bool{false, false, false}, tuneRows))
-	if len(fatal) > 0 {
-		return fmt.Errorf("cannot test with %s in this state", strings.Join(fatal, ", "))
+	if err := reportChecks("HOST SETTINGS", configureSystem(ifnames, ethertypes)); err != nil {
+		return err
 	}
 
 	cfg := config{

system.go

@@ -282,6 +282,24 @@ func (r checkResult) detail() string {
 	return r.state
 }
 
+func reportChecks(title string, results []checkResult) error {
+	var rows [][]string
+	var fatal []string
+	for _, r := range results {
+		rows = append(rows, []string{r.item, r.status(), r.detail()})
+		if r.fatal {
+			fatal = append(fatal, r.item)
+		}
+	}
+	fmt.Println(renderBox(title,
+		[]string{"CHECK", "STATUS", "DETAIL"},
+		[]bool{false, false, false}, rows))
+	if len(fatal) > 0 {
+		return fmt.Errorf("cannot test with %s in this state", strings.Join(fatal, ", "))
+	}
+	return nil
+}
+
 func ethtoolCall(fd int, ifname string, data unsafe.Pointer) error {
 	var ifr dataIfreq
 	if len(ifname) >= unix.IFNAMSIZ {

ui.go

@@ -58,7 +58,7 @@ type display struct {
 }
 
 func newDisplay() (*display, error) {
-	fb, err := openFramebuffer("/dev/fb0")
+	fb, err := openFramebuffer(fbPath)
 	if err != nil {
 		return nil, err
 	}