scemd_fanspeed_hook

hooks scemd's ioctl function, check if it's fanspeed controlling code, then redirecting it to our own fan speed control logic.

The code contains speed control code for ITE IT8728F chip, from the below credits you can find the IT8772E

Usage:

1. Compile: make

2. On Synology, move the /usr/syno/bin/scemd to /usr/syno/bin/scemd.orig

3. Copy the compiled scemd and scemd_hijack.so to /usr/syno/bin

4. (Optional) tweak your settings in /usr/syno/etc/scemd.xml and /usr/syno/etc.defaults/scemd.xml

Credits:

• terramaster-fancontrol: offering a brilliant idea to change the fanspeed
• ldpreloadhook: great template code for ioctl hook!

For developers

• I found the magic ioctl request code by reverse engineering the scemd, libsynoscemd.so.1 and libhwcontrol.so.1. The ScemFanSpeedAdjuster function in libsynoscemd.so.1 will do the call to SYNOFanDebugPrint in libhwcontrol.so.1, then you'll find everything looking at SYNOFanDebugPrint's cross references :)
• You can enable verbose debug log by echo 1 > /tmp/m2tmp.txt