Re: [RFC net-next 13/22] net: add queue config validation callback

[Stanislav Fomichev <stfomichev@gmail.com>]

On 04/21, Jakub Kicinski wrote:
> I imagine (tm) that as the number of per-queue configuration
> options grows some of them may conflict for certain drivers.
> While the drivers can obviously do all the validation locally
> doing so is fairly inconvenient as the config is fed to drivers
> piecemeal via different ops (for different params and NIC-wide
> vs per-queue).
> 
> Add a centralized callback for validating the queue config
> in queue ops. The callback gets invoked before each queue restart
> and when ring params are modified.
> 
> For NIC-wide changes the callback gets invoked for each active
> (or active to-be) queue, and additionally with a negative queue
> index for NIC-wide defaults. The NIC-wide check is needed in
> case all queues have an override active when NIC-wide setting
> is changed to an unsupported one. Alternatively we could check
> the settings when new queues are enabled (in the channel API),
> but accepting invalid config is a bad idea. Users may expect
> that resetting a queue override will always work.

[..]

> The "trick" of passing a negative index is a bit ugly, we may
> want to revisit if it causes confusion and bugs. Existing drivers
> don't care about the index so it "just works".

+1, someone is gonna be bitten by it :-) Separate bool might be as ugly,
but more explicit, idk.