Messages in this thread | | | From | Vincent MAILHOL <> | Date | Sat, 9 Oct 2021 14:37:06 +0900 | Subject | Re: [PATCH v1] can: netlink: report the CAN controller mode supported flags |
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On Sun. 3 Oct 2021 at 13:40, Vincent Mailhol <mailhol.vincent@wanadoo.fr> wrote: > This patch introduces a method for the user to check both the > supported and the static capabilities. > > Currently, the CAN netlink interface provides no easy ways to check > the capabilities of a given controller. The only method from the > command line is to try each CAN_CTRLMODE_ individually to check > whether the netlink interface returns an -EOPNOTSUPP error or not > (alternatively, one may find it easier to directly check the source > code of the driver instead...) > > It appears that, currently, the struct can_ctrlmode::mask field is > only used in one direction: from the userland to the kernel. So we can > just reuse this field in the other direction (from the kernel to > userland). But, because the semantic is different, we use a union to > give this field a proper name: supported. > > Below table explains how the two fields can_ctrlmode::supported and > can_ctrlmode::flags, when masked with any of the CAN_CTRLMODE_* bit > flags, allow us to identify both the supported and the static > capabilities: > > supported & flags & Controller capabilities > CAN_CTRLMODE_* CAN_CTRLMODE_* > ------------------------------------------------------------------------ > false false Feature not supported (always disabled) > false true Static feature (always enabled) > true false Feature supported but disabled > true true Feature supported and enabled > > N.B.: This patch relies on the fact that a given CAN_CTRLMODE_* > feature can not be set for both can_priv::ctrlmode_supported and > can_priv::ctrlmode_static at the same time. c.f. comments in struct > can_priv [1]. Else, there would be no way to distinguish which > features were statically enabled.
Actually, can_priv::ctrlmode_static can be derived from the other ctrlmode fields. I will send a v2 in which I will add a patch to replace that field with an inline function.
Yours sincerely, Vincent Mailhol
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