attempt to write docs

README.md

@@ -1,10 +1,12 @@
 libudev-zero
 ============
 
-Drop-in replacement for libudev intended to work without daemon
+Drop-in replacement for libudev enables you to use whatever
+device manager you like without worrying about udev dependency at all!
 
 What Works
 ----------
+
 * [x] xorg-server
 * [x] libinput
 * [x] wlroots
@@ -32,6 +34,45 @@ make PREFIX=/usr install # will overwrite existing udev libraries if any
 # here we go !
 ```
 
+Hotplugging
+-----------
+
+There is no complicated or overengineered way to use hotplugging. Everything is
+portable as much as possible. To use hotplugging the only thing you need is
+uevent's receiver (device manager, busybox `uevent`, CONFIG_UEVENT_HELPER, ...).
+I will describe only mdev and CONFIG_UEVENT_HELPER because their usage is very basic.
+For busybox `uevent` you need to write your own parser which is kinda ... complex.
+
+UDEV_MONITOR_DIR is arbitrary directory where uevent files stored.
+Default is `/tmp/.libudev-zero`. You can change it at build time by appending
+`-DUDEV_MONITOR_DIR=<dir>` to CFLAGS. I don't recommend setting UDEV_MONITOR_DIR
+to regular fs (i.e non-tmpfs) because unneeded files aren't automatically discarded
+after reboot or termination (yet).
+
+* mdev
+
+  - merge [mdev.conf](contrib/mdev.conf) with your mdev.conf
+  - restart mdev daemon
+
+* CONFIG_UEVENT_HELPER
+
+  - ensure that CONFIG_UEVENT_HELPER enabled in kernel
+  - add full path of [helper.sh](contrib/helper.sh) (must be executable) or
+    [helper.c](contrib/helper.c) (compile it first) to /proc/sys/kernel/hotplug
+
+    example:
+    ```sh
+    echo /full/path/to/helper > /proc/sys/kernel/hotplug # will use default UDEV_MONITOR_DIR
+    OR
+    echo "/full/path/to/helper <dir>" > /proc/sys/kernel/hotplug # change <dir> to your UDEV_MONITOR_DIR
+    ```
+
+* run application which uses hotplugging (e.g xorg-server)
+* unplug and plug something to test working capacity
+
+That's all! If you realized that this doesn't work for you,
+you can always open an issue and describe your bug.
+
 TODO
 ----