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docs: netlink: clarify the historical baggage of Netlink flags
authorJakub Kicinski <kuba@kernel.org>
Tue, 27 Sep 2022 21:23:06 +0000 (14:23 -0700)
committerJakub Kicinski <kuba@kernel.org>
Fri, 30 Sep 2022 01:39:39 +0000 (18:39 -0700)
commit5493a2ad0d20944b16aba7ed7a951a43ad1f5fba
treec5b08ba52c12f879cd13daee72ec7d20c4ab1a02
parentaccc3b4a572bba903a801a393532272727f83f5b
docs: netlink: clarify the historical baggage of Netlink flags

nlmsg_flags are full of historical baggage, inconsistencies and
strangeness. Try to document it more thoroughly. Explain the meaning
of the ECHO flag (and while at it clarify the comment in the uAPI).
Handwave a little about the NEW request flags and how they make
sense on the surface but cater to really old paradigm before commands
were a thing.

I will add more notes on how to make use of ECHO and discouragement
for reuse of flags to the kernel-side documentation.

Link: https://lore.kernel.org/r/20220927212306.823862-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Documentation/userspace-api/netlink/intro.rst
include/uapi/linux/netlink.h