Subject: Re: [PATCH v11 2/2] binder: report txn errors via generic netlink

From: Carlos Llamas <[email-masked]>
Date: Thu, 9 Jan 2025 19:30:48 +0000

On Thu, Jan 09, 2025 at 06:51:59PM +0000, Carlos Llamas wrote:
> Did you happen to look into netlink_register_notifier()? That seems like
> an option to keep the device vs netlink socket interface from mixing up.
> I believe we could check for NETLINK_URELEASE events and do the cleanup
> then. I'll do a quick try.

Yeah, this quick prototype worked for me. Although I haven't looked at
the api details closely.

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 536be42c531e..fa2146cf02a7 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
+static int binder_netlink_notify(struct notifier_block *nb,
+	+	+	+	 unsigned long action,
+	+	+	+	 void *data)
+{
+	struct netlink_notify *n = data;
+	struct binder_device *device;
+
+	if (action != NETLINK_URELEASE)
+	+	return NOTIFY_DONE;
+
+	hlist_for_each_entry(device, &binder_devices, hlist) {
+	+	if (device->context.report_portid == n->portid)
+	+	+	pr_info("%s: socket released\n", __func__);
+	}
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block binder_netlink_notifier = {
+	.notifier_call = binder_netlink_notify,
+};
+
 static int __init binder_init(void)
 {
+	int ret;
@@ -7244,6 +7259,8 @@ static int __init binder_init(void)
+	+	goto err_init_binder_device_failed;
+	}

+	netlink_register_notifier(&binder_netlink_notifier);
+
+	return ret;

 err_init_binder_device_failed:

With that change we get notified when the socket that registered the
report exits:

  root@debian:~# ./binder-netlink
  report setup complete!
  ^C[   63.682485] binder: binder_netlink_notify: socket released

I don't know if this would be the preferred approach to "install" a
notification callback with a netlink socket but it works. wdyt?

--
Carlos Llamas