container/init: split setup ops into individual files

This significantly increases readability.

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

container/initplace.go

@@ -0,0 +1,81 @@
+package container
+
+import (
+	"encoding/gob"
+	"fmt"
+	"os"
+	"slices"
+	. "syscall"
+)
+
+const (
+	// intermediate root file name pattern for [TmpfileOp]
+	intermediatePatternTmpfile = "tmp.*"
+)
+
+func init() { gob.Register(new(TmpfileOp)) }
+
+// Place appends an [Op] that places a file in container path [TmpfileOp.Path] containing [TmpfileOp.Data].
+func (f *Ops) Place(name *Absolute, data []byte) *Ops {
+	*f = append(*f, &TmpfileOp{name, data})
+	return f
+}
+
+// PlaceP is like Place but writes the address of [TmpfileOp.Data] to the pointer dataP points to.
+func (f *Ops) PlaceP(name *Absolute, dataP **[]byte) *Ops {
+	t := &TmpfileOp{Path: name}
+	*dataP = &t.Data
+
+	*f = append(*f, t)
+	return f
+}
+
+// TmpfileOp places a file on container Path containing Data.
+type TmpfileOp struct {
+	Path *Absolute
+	Data []byte
+}
+
+func (t *TmpfileOp) early(*setupState) error { return nil }
+func (t *TmpfileOp) apply(state *setupState) error {
+	if t.Path == nil {
+		return EBADE
+	}
+
+	var tmpPath string
+	if f, err := os.CreateTemp(FHSRoot, intermediatePatternTmpfile); err != nil {
+		return wrapErrSelf(err)
+	} else if _, err = f.Write(t.Data); err != nil {
+		return wrapErrSuffix(err,
+			"cannot write to intermediate file:")
+	} else if err = f.Close(); err != nil {
+		return wrapErrSuffix(err,
+			"cannot close intermediate file:")
+	} else {
+		tmpPath = f.Name()
+	}
+
+	target := toSysroot(t.Path.String())
+	if err := ensureFile(target, 0444, state.ParentPerm); err != nil {
+		return err
+	} else if err = hostProc.bindMount(
+		tmpPath,
+		target,
+		MS_RDONLY|MS_NODEV,
+		false,
+	); err != nil {
+		return err
+	} else if err = os.Remove(tmpPath); err != nil {
+		return wrapErrSelf(err)
+	}
+	return nil
+}
+
+func (t *TmpfileOp) Is(op Op) bool {
+	vt, ok := op.(*TmpfileOp)
+	return ok && t.Path == vt.Path && slices.Equal(t.Data, vt.Data)
+}
+func (*TmpfileOp) prefix() string { return "placing" }
+func (t *TmpfileOp) String() string {
+	return fmt.Sprintf("tmpfile %q (%d bytes)", t.Path, len(t.Data))
+}