[Kernel] kobject uevent in kernel

⚫ Sendig kobject uevent to user space from kernel
    ⚬ Concept
        • Execute user-space binary with predefined + customized environment variables.
        • Send message to pre-defined netlink socket unit created by kernel.

    ⚬ From souce code (hotplug)
        • kernel node [kernel/sysctl.c]
        : /proc/sys/kernel/hotplug

        • kobject_uevent_env() [kobject_uevent.c]
            default user process executable image path
                -> CONFIG_UEVENT_HELPER_PATH
        • kernel/sysctl.c
            'uevent_helper' value can be RWed through 'hotplug' node of sysctl.

    ⚬ From souce code (netlink)
        • kobject_uevent_env() [kobject_uevent.c]
            : #if defined(CONFIG_NET)
            write message to netlink socket unit (NETLINK_KOBJECT_UEVENT)
        • netlink.h
            netlink units
        • Creating in userspace
            socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT)