How to assign sockaddr_nl->nl_groups when using connector

Evgeniy Polyakov zbr at
Wed Mar 20 18:29:20 UTC 2013


On Tue, Mar 19, 2013 at 10:15:43AM +0800, vaughan (vaughan.cao at wrote:
> I am not quite sure how to assign nl_groups when using connector. You
> Documentation/connector/connector.txt don't explain it very clearly. I
> thought it's a bitmask representing only 32 groups.
> If I just want to subscribe only one group such as CN_KVP_IDX, what
> shall I do? Which one below is correct?
> a) l_local.nl_groups = CN_KVP_IDX;
> Or
> b) l_local.nl_groups = 1 << (CN_KVP_IDX -1)
> and bind with bind(s, (struct sockaddr *)&l_local, sizeof(struct
> sockaddr_nl)).

Iirc, first groups, created before bitmap-to-number conversion were
actually bitmaps, but then broadcast interface was obsoleted.

One should use NETLINK_ADD_MEMBERSHIP interface and specify gruop number

> I ran your example in Documentation/connector/. 'l_local.nl_groups = -1'
> in ucon.c seems subscribe all channels, because if I start cgred
> service, ucon will receive messages with idx=1.
> And it seems setsockopt is not needed now, for it is done by
> netlink_autobind? You even comment it out using '#if 0' in
> Documentation/connector/ucon.c.
> Could you do me a favor to check
> to see if my understanding is correct or not? Thanks.

Yes, you are right.

	Evgeniy Polyakov

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