I read this in the latest news post:
Lastly, on upgrading filesystem users of kernels prior to linux-3.4 will get a warning about permissions on /sys. This is nothing to worry about, as of linux-3.4 the permissions will be 555, and this upgrade reflects this in the filesystem package.
...huh? I tried Googling this but came up empty-handed. Even the kernel changelog didn't mention sysfs much, and nothing about changing the permissions (unless I just missed it somehow). Is this an Arch-specific change?
While writing this post I realized that my initial alarm was unwarranted: at first I thought that meant I couldn't write to anything in /sys. In a supreme fit of silliness, I even tried
sudo echo -n mem > /sys/power/state
and interpreted the subsequent "Permission denied" as proof that something was horribly wrong. But of course starting with
fixed that, and my fears were alleviated. Turns out sysfs is still mounted rw and all the usual files are still 644.
So now that I think about it having /sys be 555 is kind of obvious. Now I'm rather bewildered as to why the directories inside sysfs are 755! Under what circumstances would userspace create, delete or rename a file inside the sysfs? I'm by no means a Linux programmer (I'm an EE currently working on programming a microcontroller), so I'll bet I'm missing something obvious, but I'm curious what it is.
Thanks for finding the commit. Sounds like they just did it for consistency with /proc, and probably no one should be creating or deleting anything in there anyway. Curiosity sated