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

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Message-ID: <aAe6dW1pU9wjAvem@mini-arch>
Date: Tue, 22 Apr 2025 08:49:09 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
	pabeni@...hat.com, andrew+netdev@...n.ch, horms@...nel.org,
	donald.hunter@...il.com, sdf@...ichev.me, almasrymina@...gle.com,
	dw@...idwei.uk, asml.silence@...il.com, ap420073@...il.com,
	jdamato@...tly.com, dtatulea@...dia.com, michael.chan@...adcom.com
Subject: Re: [RFC net-next 13/22] net: add queue config validation callback

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.