Good morning!

Recently, I have found an issue with `rtnetlink` library that seems to be not intended and/or documented. I have asked about it several times, including here and it was also reported here. Neither in related RFC document nor in rtnetlink manuals the issue is described or mentioned.

In a few words, the issue is: for some reason, rtnetlink GETADDR request works only with NLM_F_ROOT or NLM_F_DUMP flags. Consequently, for instance, filtering by ifa_index field, that would *theoretically* according to docs, allow us to receive address info for 1 specific interface only (by ID) , is not possible. For comparison, similar functionality to GETLINK request (getting information about exactly 1 link by index) is indeed very possible. Instead of the expected output (information about 1 interface only), what is returned is an error message with errno -95, which, as I suppose, can be read as "operation not permitted".

To this email, I attach a small C file illustrating my issue. Feel free to change IFACE_ID define for ID of any network interface present in your system. It illustrates the error.

Please, let me know what you think about this issue. Am I missing something or does it really needs fixing or at least documenting? Best regards, Aleksandr Sergeev.

P.S. I have been told that this issue probably won't be addressed, because it "can easily be fixed in user space", however I believe in Linux kernel maintainers team dedication for clear, well-documented and bug-free code; so if this issue is not hard to fix, I would suggest addressing it at least in docs. If it can be useful, I would be more than grateful to provide my help with it.