On Sat, Oct 01, 2022 at 12:46:24AM +0000, Charles Lohr via networkmanager-list wrote:
In our application, we need to maintain connection to an AP and it needs to stay low latency for a variety
of reasons. Whenever networks are scanned, for us they create an unacceptable level of latency (>50ms in
many cases) on the connection.
Sometimes we stop NetworkManager from running with `pkill -STOP NetworkManager` and `pkill -CONT
NetworkManager` but, for a variety of reasons this is disadvantageous.
I've seen references to people online saying you can prevent scanning once connected by specifying a BSSID,
but I don't see how that can be done with libnm.
Currently we use the following, where path can be gotten from either a scan or `nm_connection_get_path`
```
nm_client_activate_connection_async ( m_pClient, conn, (NMDevice*)m_pDevice, sAccessPointPath.c_str(),
nullptr, []( GObject* pObj, GAsyncResult* res, gpointer pContext ) {...} );
```
What mechanism can we use to specify that a given path should lock it's BSSID when using NetworkManager via
libnm?
Hi, to disable scanning, you can set the property NM_SETTING_WIRELESS_BSSID of the setting NMSettingWireless to the AP's BSSID when the connection profile is created. To get the AP's BSSID use nm_access_point_get_bssid(). References: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/1.40.0/examples/C/glib/add-connection-libnm.c#L44 https://networkmanager.dev/docs/api/latest/nm-settings-dbus.html#id-1.2.9.4.48 ("bssid property") https://networkmanager.dev/docs/libnm/latest/NMAccessPoint.html#nm-access-point-get-bssid https://fedoramagazine.org/using-python-and-networkmanager-to-control-the-network/
Second question: Are there any mechanisms we can use to lock out other apps from requesting scans from NetworkManager? This solution would be preferred for our application because scans have such a significant impact on the system. Or is there a way to just outright disable all scanning via NetworkManger for a period of time?
If the feature is enabled at build time, NM can use polkit to authorize D-Bus requests. In particular, there is a "Wi-Fi scan" permission that grants access to scans. I think you can use polkit rules to restrict the access to a certain user or process; however, note that any process running as root bypasses polkit checks and is always authorized. References: https://networkmanager.dev/docs/libnm/latest/libnm-nm-dbus-interface.html#NMClientPermission https://networkmanager.dev/docs/api/latest/nmcli.html (nmcli general permissions) Beniamino
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