Right, so if you look at the android common kernel implementation. https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline/net/netfilter/xt_IDLETIMER.c#201 (and in particular grep for send_nl_msg throughout the file) the core difference is the call to notify_netlink_uevent() at https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline/net/netfilter/xt_IDLETIMER.c#101 this function is also defined in the same file, and it ends up calling kobject_uevent_env(idletimer_tg_kobj, KOBJ_CHANGE, envp); with INTERFACE, STATE, UID and TIME_NS metadata. this is later parsed in netd C++: https://android.googlesource.com/platform/system/netd/+/refs/heads/master/server/NetlinkHandler.cpp#208 which then via notifyInterfaceClassActivityChanged() I believe generates a binder call into the java network stack for further processing. void NetlinkHandler::notifyInterfaceClassActivityChanged(int label, bool isActive, int64_t timestamp, int uid) { LOG_EVENT_FUNC(BINDER_RETRY, onInterfaceClassActivityChanged, isActive, label, timestamp, uid); } Ultimately the goal is to know WHO (uid - on Android it's 1 unix uid per {user,app} combination) generated traffic activity, WHEN (timestamp) and WHERE (label ie. interface). ie. To figure out whether an interface is idle or not and can be shutdown, or powersaved, etc. WHO matters because some users (apps!) might be insufficiently important (lack of background data privs) to prevent a network device powersavings/sleep/disconnect or to cause a wakeup (I think). My understanding is the 'timer' thing (aka HARDIDLETIMER) was added because phones are almost constantly entering suspend state, so we care about real clock time (CLOCK_BOOTTIME) rather than cpu activity time (CLOCK_MONOTONIC which doesn't include time the device is suspended). I think this could probably be eventually switched to use the sysfs notification mechanism, but we can't change that on any of the already shipped devices and it's kind of late even for devices shipping this year, and that system would presumably need to be extended to support uids. On Tue, Mar 31, 2020 at 4:28 PM Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote: > > On Tue, Mar 31, 2020 at 02:21:00PM -0700, Maciej Żenczykowski wrote: > > Right, this is not in 5.6 as it's only in net-next atm as it was only > > merged very recently. > > I mentioned this in the commit message. > > > > I'm not sure what you mean by code that uses this. > > You can checkout aosp source and look there... > > There's the kernel code (that's effectively already linked from the > > commit message), and the iptables userspace changes ( > > https://android.googlesource.com/platform/external/iptables/+/refs/heads/master/extensions/libxt_IDLETIMER.c#39 > > OK, so this is field ised set in userspace. > > > ), and the netd C++/Java layer that uses iptables -j IDLETIMER > > --send_nl_msg 1 ( > > https://android.googlesource.com/platform/system/netd/+/refs/heads/master/server/IdletimerController.cpp#151 > > ) and the resulting notifications parsing (can't easily find it atm). > > > > If you mean by code that uses this patch... that's impossible as this > > patch doesn't implement a usable feature. > > It just moves the offset. > > > > Could you clarify what you're asking for? > > Maybe I'm misunderstanding. How is this field used in aosp? > > I mean, if --send_nl_msg 1 is passed, how does the existing behaviour > changes?
