[...] It is planned to merge all three classification directories into one place at /sys/subsystem, following the layout of the bus directories. All buses and classes, including the converted block subsystem, will show up there.
The devices belonging to a subsystem will create a symlink in the "devices" directory at /sys/subsystem/<name>/devices.
If /sys/subsystem exists, /sys/bus, /sys/class and /sys/block can be ignored. If it does not exist, you always have to scan all three places, as the kernel is free to move a subsystem from one place to the other, as long as the devices are still reachable by the same subsystem name.
Well, when I try to learn the layout of the /sys filesystem of Linux kernel, I see no /sys/subsystem directory in my Ubuntu OS (I use Ubuntu 14.04).
I did a quick Google search and only found an LKML discussion about the directory unification, but I don't see anything else beside Kay Sievers' note. (A git log on Documentation/sysfs-rules.txt also shows it's by him, too.)
My question is, do I miss anything? Why is the directory not available? Or is the directory merge never actually happened in kernel development and is the document wrong?