internal/uevent: synthetic events for coldboot

This causes the kernel to regenerate events that happened before earlyinit started.

Signed-off-by: Ophestra <cat@gensokyo.uk>

2 files changed, 298 insertions, 0 deletions

diff --git a/internal/uevent/coldboot.go b/internal/uevent/coldboot.go
new file mode 100644
index 00000000..07f6497f
--- /dev/null
+++ b/internal/uevent/coldboot.go
@@ -0,0 +1,71 @@
+package uevent
+
+import (
+	"context"
+	"errors"
+	"io/fs"
+	"log"
+	"os"
+	"path/filepath"
+)
+
+// synthAdd is prepared bytes written to uevent to cause a synthetic add event
+// to be emitted during coldboot.
+var synthAdd = []byte(KOBJ_ADD.String())
+
+// Coldboot writes "add" to every uevent file that it finds in /sys/devices.
+// This causes the kernel to regenerate the uevents for these paths.
+//
+// The specified pathname must present the sysfs root.
+//
+// Note that while [AOSP documentation] claims to also scan /sys/class and
+// /sys/block, this is no longer the case, and the documentation was not updated
+// when this changed.
+//
+// [AOSP documentation]: https://android.googlesource.com/platform/system/core/+/master/init/README.ueventd.md
+func Coldboot(
+	ctx context.Context,
+	pathname string,
+	visited chan<- string,
+	handleWalkErr func(error) error,
+) error {
+	if handleWalkErr == nil {
+		handleWalkErr = func(err error) error {
+			if errors.Is(err, fs.ErrNotExist) {
+				log.Println("coldboot", err)
+				return nil
+			}
+			return err
+		}
+	}
+
+	return filepath.WalkDir(filepath.Join(pathname, "devices"), func(
+		path string,
+		d fs.DirEntry,
+		err error,
+	) error {
+		if err != nil {
+			return handleWalkErr(err)
+		}
+		if err = ctx.Err(); err != nil {
+			return err
+		}
+
+		if d.IsDir() || d.Name() != "uevent" {
+			return nil
+		}
+		if err = os.WriteFile(path, synthAdd, 0); err != nil {
+			return handleWalkErr(err)
+		}
+
+		select {
+		case visited <- path:
+			break
+
+		case <-ctx.Done():
+			return ctx.Err()
+		}
+
+		return nil
+	})
+}
diff --git a/internal/uevent/coldboot_test.go b/internal/uevent/coldboot_test.go
new file mode 100644
index 00000000..e3491e64
--- /dev/null
+++ b/internal/uevent/coldboot_test.go
@@ -0,0 +1,227 @@
+package uevent_test
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"reflect"
+	"slices"
+	"sync"
+	"syscall"
+	"testing"
+
+	"hakurei.app/check"
+	"hakurei.app/internal/pkg"
+	"hakurei.app/internal/uevent"
+)
+
+func TestColdboot(t *testing.T) {
+	t.Parallel()
+
+	d := t.TempDir()
+	if err := os.Chmod(d, 0700); err != nil {
+		t.Fatal(err)
+	}
+
+	for _, s := range []string{
+		"devices",
+		"devices/sub",
+		"devices/empty",
+		"block",
+	} {
+		if err := os.MkdirAll(filepath.Join(d, s), 0700); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	for _, f := range [][2]string{
+		{"devices/uevent", ""},
+		{"devices/sub/uevent", ""},
+		{"block/uevent", ""},
+	} {
+		if err := os.WriteFile(
+			filepath.Join(d, f[0]),
+			[]byte(f[1]),
+			0600,
+		); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	var wg sync.WaitGroup
+	defer wg.Wait()
+
+	visited := make(chan string)
+	var got []string
+	wg.Go(func() {
+		for path := range visited {
+			got = append(got, path)
+		}
+	})
+
+	err := uevent.Coldboot(t.Context(), d, visited, func(err error) error {
+		t.Errorf("handleWalkErr: %v", err)
+		return err
+	})
+	close(visited)
+	if err != nil {
+		t.Fatalf("Coldboot: error = %v", err)
+	}
+
+	wg.Wait()
+	want := []string{
+		"devices/sub/uevent",
+		"devices/uevent",
+	}
+	for i, rel := range want {
+		want[i] = filepath.Join(d, rel)
+	}
+	if !slices.Equal(got, want) {
+		t.Errorf("Coldboot: %#v, want %#v", got, want)
+	}
+
+	var checksum pkg.Checksum
+	if err = pkg.HashDir(&checksum, check.MustAbs(d)); err != nil {
+		t.Fatalf("HashDir: error = %v", err)
+	}
+
+	wantChecksum := pkg.MustDecode("mEy_Lf5KotThm7OwMx7yTKZh5HCCyaB41pVAvI9uDMgVQFM91iosBLYsRm8bDsX8")
+	if checksum != wantChecksum {
+		t.Errorf(
+			"Coldboot: checksum = %s, want %s",
+			pkg.Encode(checksum),
+			pkg.Encode(wantChecksum),
+		)
+	}
+}
+
+func TestColdbootError(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		dF   func(t *testing.T, d string) (wantErr error)
+		vF   func(<-chan string, context.Context, context.CancelFunc)
+		hF   func(d string, err error) error
+	}{
+		{"walk", func(t *testing.T, d string) (wantErr error) {
+			wantErr = &os.PathError{
+				Op:   "open",
+				Path: filepath.Join(d, "devices"),
+				Err:  syscall.EACCES,
+			}
+			if err := os.Mkdir(filepath.Join(d, "devices"), 0); err != nil {
+				t.Fatal(err)
+			}
+			return
+		}, nil, nil},
+
+		{"write", func(t *testing.T, d string) (wantErr error) {
+			wantErr = &os.PathError{
+				Op:   "open",
+				Path: filepath.Join(d, "devices/uevent"),
+				Err:  syscall.EACCES,
+			}
+			if err := os.Mkdir(filepath.Join(d, "devices"), 0700); err != nil {
+				t.Fatal(err)
+			} else if err = os.WriteFile(filepath.Join(d, "devices/uevent"), nil, 0); err != nil {
+				t.Fatal(err)
+			}
+			return
+		}, nil, nil},
+
+		{"deref", func(t *testing.T, d string) (wantErr error) {
+			if err := os.Mkdir(filepath.Join(d, "devices"), 0700); err != nil {
+				t.Fatal(err)
+			} else if err = os.Symlink("/proc/nonexistent", filepath.Join(d, "devices/uevent")); err != nil {
+				t.Fatal(err)
+			}
+			return
+		}, nil, nil},
+
+		{"deref handle", func(t *testing.T, d string) (wantErr error) {
+			if err := os.Mkdir(filepath.Join(d, "devices"), 0700); err != nil {
+				t.Fatal(err)
+			} else if err = os.Symlink("/proc/nonexistent", filepath.Join(d, "devices/uevent")); err != nil {
+				t.Fatal(err)
+			}
+			return
+		}, nil, func(d string, err error) error {
+			if reflect.DeepEqual(err, &os.PathError{
+				Op:   "open",
+				Path: filepath.Join(d, "devices/uevent"),
+				Err:  syscall.ENOENT,
+			}) {
+				return nil
+			}
+			return err
+		}},
+
+		{"cancel early", func(t *testing.T, d string) (wantErr error) {
+			wantErr = context.Canceled
+			if err := os.Mkdir(filepath.Join(d, "devices"), 0700); err != nil {
+				t.Fatal(err)
+			}
+			return
+		}, func(visited <-chan string, ctx context.Context, cancel context.CancelFunc) {
+			if visited == nil {
+				cancel()
+			}
+			return
+		}, nil},
+
+		{"cancel", func(t *testing.T, d string) (wantErr error) {
+			wantErr = context.Canceled
+			if err := os.Mkdir(filepath.Join(d, "devices"), 0700); err != nil {
+				t.Fatal(err)
+			} else if err = os.WriteFile(filepath.Join(d, "devices/uevent"), nil, 0600); err != nil {
+				t.Fatal(err)
+			} else if err = os.Mkdir(filepath.Join(d, "devices/sub"), 0700); err != nil {
+				t.Fatal(err)
+			} else if err = os.WriteFile(filepath.Join(d, "devices/sub/uevent"), nil, 0600); err != nil {
+				t.Fatal(err)
+			}
+			return
+		}, func(visited <-chan string, ctx context.Context, cancel context.CancelFunc) {
+			if visited == nil {
+				return
+			}
+			<-visited
+			cancel()
+			return
+		}, nil},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			d := t.TempDir()
+			wantErr := tc.dF(t, d)
+
+			var wg sync.WaitGroup
+			defer wg.Wait()
+
+			ctx, cancel := context.WithCancel(t.Context())
+			defer cancel()
+
+			var visited chan string
+			if tc.vF != nil {
+				tc.vF(nil, ctx, cancel)
+				visited = make(chan string)
+				defer close(visited)
+				wg.Go(func() { tc.vF(visited, ctx, cancel) })
+			}
+
+			var handleWalkErr func(error) error
+			if tc.hF != nil {
+				handleWalkErr = func(err error) error {
+					return tc.hF(d, err)
+				}
+			}
+
+			if err := uevent.Coldboot(ctx, d, visited, handleWalkErr); !reflect.DeepEqual(err, wantErr) {
+				t.Errorf("Coldboot: error = %v, want %v", err, wantErr)
+			}
+		})
+	}
+}