net: bridge: add support for user-controlled bool options

We have been adding many new bridge options, a big number of which are boolean but still take up netlink attribute ids and waste space in the skb. Recently we discussed learning from link-local packets[1] and decided yet another new boolean option will be needed, thus introducing this API to save some bridge nl space. The API supports changing the value of multiple boolean options at once via the br_boolopt_multi struct which has an optmask (which options to set, bit per opt) and optval (options' new values). Future boolean options will only be added to the br_boolopt_id enum and then will have to be handled in br_boolopt_toggle/get. The API will automatically add the ability to change and export them via netlink, sysfs can use the single boolopt function versions to do the same. The behaviour with failing/succeeding is the same as with normal netlink option changing. If an option requires mapping to internal kernel flag or needs special configuration to be enabled then it should be handled in br_boolopt_toggle. It should also be able to retrieve an option's current state via br_boolopt_get. v2: WARN_ON() on unsupported option as that shouldn't be possible and also will help catch people who add new options without handling them for both set and get. Pass down extack so if an option desires it could set it on error and be more user-friendly. [1] https://www.spinics.net/lists/netdev/msg532698.html

NANikolay Aleksandrov committed 7 years ago