container/init: split setup ops into individual files

This significantly increases readability.

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

container/initproc.go

@@ -0,0 +1,41 @@
+package container
+
+import (
+	"encoding/gob"
+	"fmt"
+	"os"
+	. "syscall"
+)
+
+func init() { gob.Register(new(MountProcOp)) }
+
+// Proc appends an [Op] that mounts a private instance of proc.
+func (f *Ops) Proc(target *Absolute) *Ops {
+	*f = append(*f, &MountProcOp{target})
+	return f
+}
+
+// MountProcOp mounts a new instance of [FstypeProc] on container path Target.
+type MountProcOp struct {
+	Target *Absolute
+}
+
+func (p *MountProcOp) early(*setupState) error { return nil }
+func (p *MountProcOp) apply(state *setupState) error {
+	if p.Target == nil {
+		return EBADE
+	}
+	target := toSysroot(p.Target.String())
+	if err := os.MkdirAll(target, state.ParentPerm); err != nil {
+		return wrapErrSelf(err)
+	}
+	return wrapErrSuffix(Mount(SourceProc, target, FstypeProc, MS_NOSUID|MS_NOEXEC|MS_NODEV, zeroString),
+		fmt.Sprintf("cannot mount proc on %q:", p.Target.String()))
+}
+
+func (p *MountProcOp) Is(op Op) bool {
+	vp, ok := op.(*MountProcOp)
+	return ok && ((p == nil && vp == nil) || p == vp)
+}
+func (*MountProcOp) prefix() string   { return "mounting" }
+func (p *MountProcOp) String() string { return fmt.Sprintf("proc on %q", p.Target) }