Misleading information about the "all" special device

[dermoth]

For example: https://sysctl-explorer.net/net/ipv4/rp_filter/

The doc says:

“all” is a special interface: changes the settings for all interfaces.

This is misleading... In most cases the all value is simply OR'ed or max()'ed with the device value, although for some sysctls it may be even more complex (there's an OR define for some, though maybe they actually apply all to all devices?) For rp_filter setting all definitely doesn't apply to the actual devices on the kernels I tested.

The defines I'm referring to are available here:
https://elixir.bootlin.com/linux/latest/source/include/linux/inetdevice.h#L76

There were also some change over the years... rp_filter changed in the 2.6.2x kernels, but it's also around when they added value "2". Even older kernels in the 2.6 series seems to AND the values.