Getting notifications of the tasks file

["Víctor Fernández Martínez" <vfernandez-JE8hqn47KVKB+jHODAdFcQ@public.gmane.org>]

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I'm trying to use the eventfd notification API to get notified when the tasks 
file changes. This way I would like to know when child processes are spawned 
and when they exit. However, I always get EINVAL when writing to 
cgroup.event_control. Even cgroup_event_listener.c returns that error:

# cat /sys/fs/cgroup/memory/grp0/tasks 
3590
23902
# ./cgroup_event_listener /sys/fs/cgroup/memory/grp0/tasks 0
Cannot write to cgroup.event_control: Invalid argument

I have also tried to monitor cgroup.procs.

Is it possible to monitor the tasks file at all or is this a bug? If 0 is a 
wrong argument, which argument should I use instead?


Thanks.


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