container/init: split setup ops into individual files

This significantly increases readability.

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

container/initremount.go

@@ -0,0 +1,34 @@
+package container
+
+import (
+	"encoding/gob"
+	"fmt"
+	"syscall"
+)
+
+func init() { gob.Register(new(RemountOp)) }
+
+// Remount appends an [Op] that applies [RemountOp.Flags] on container path [RemountOp.Target].
+func (f *Ops) Remount(target *Absolute, flags uintptr) *Ops {
+	*f = append(*f, &RemountOp{target, flags})
+	return f
+}
+
+// RemountOp remounts Target with Flags.
+type RemountOp struct {
+	Target *Absolute
+	Flags  uintptr
+}
+
+func (*RemountOp) early(*setupState) error { return nil }
+func (r *RemountOp) apply(*setupState) error {
+	if r.Target == nil {
+		return syscall.EBADE
+	}
+	return wrapErrSuffix(hostProc.remount(toSysroot(r.Target.String()), r.Flags),
+		fmt.Sprintf("cannot remount %q:", r.Target))
+}
+
+func (r *RemountOp) Is(op Op) bool  { vr, ok := op.(*RemountOp); return ok && *r == *vr }
+func (*RemountOp) prefix() string   { return "remounting" }
+func (r *RemountOp) String() string { return fmt.Sprintf("%q flags %#x", r.Target, r.Flags) }