sandbox: relative autoetc links

This allows nested containers to use autoetc, and increases compatibility with other implementations.

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

sandbox/ops.go

@@ -443,31 +443,26 @@ func (f *Ops) PlaceP(name string, dataP **[]byte) *Ops {
 
 func init() { gob.Register(new(AutoEtc)) }
 
-// AutoEtc creates a toplevel symlink mirror of a directory in sysroot with /etc semantics.
+// AutoEtc expands host /etc into a toplevel symlink mirror with /etc semantics.
 // This is not a generic setup op. It is implemented here to reduce ipc overhead.
-type AutoEtc struct {
-	// this is an absolute path within sysroot
-	HostEtc string
-}
+type AutoEtc struct{ Prefix string }
 
 func (e *AutoEtc) early(*Params) error { return nil }
 func (e *AutoEtc) apply(*Params) error {
-	if !path.IsAbs(e.HostEtc) {
-		return msg.WrapErr(syscall.EBADE,
-			fmt.Sprintf("path %q is not absolute", e.HostEtc))
-	}
-
 	const target = sysrootPath + "/etc/"
+	rel := e.hostRel() + "/"
+
 	if err := os.MkdirAll(target, 0755); err != nil {
 		return wrapErrSelf(err)
 	}
-
-	if d, err := os.ReadDir(toSysroot(e.HostEtc)); err != nil {
+	if d, err := os.ReadDir(toSysroot(e.hostPath())); err != nil {
 		return wrapErrSelf(err)
 	} else {
 		for _, ent := range d {
 			n := ent.Name()
 			switch n {
+			case ".host":
+
 			case "passwd":
 			case "group":
 
@@ -477,7 +472,7 @@ func (e *AutoEtc) apply(*Params) error {
 				}
 
 			default:
-				if err = os.Symlink(path.Join(e.HostEtc, n), target+n); err != nil {
+				if err = os.Symlink(rel+n, target+n); err != nil {
 					return wrapErrSelf(err)
 				}
 			}
@@ -486,11 +481,19 @@ func (e *AutoEtc) apply(*Params) error {
 
 	return nil
 }
+func (e *AutoEtc) hostPath() string { return "/etc/" + e.hostRel() }
+func (e *AutoEtc) hostRel() string  { return ".host/" + e.Prefix }
 
 func (e *AutoEtc) Is(op Op) bool {
 	ve, ok := op.(*AutoEtc)
 	return ok && ((e == nil && ve == nil) || (e != nil && ve != nil && *e == *ve))
 }
-func (*AutoEtc) prefix() string     { return "setting up" }
-func (e *AutoEtc) String() string   { return fmt.Sprintf("auto etc via %s", e.HostEtc) }
-func (f *Ops) Etc(host string) *Ops { *f = append(*f, &AutoEtc{host}); return f }
+func (*AutoEtc) prefix() string   { return "setting up" }
+func (e *AutoEtc) String() string { return fmt.Sprintf("auto etc %s", e.Prefix) }
+func (f *Ops) Etc(host, prefix string) *Ops {
+	e := &AutoEtc{prefix}
+	f.Mkdir("/etc", 0755)
+	f.Bind(host, e.hostPath(), 0)
+	*f = append(*f, e)
+	return f
+}