netdev - Re: [RFC PATCH 1/3] veth: implement support for set

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Date:   Fri, 9 Jul 2021 12:54:31 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        toke@...hat.com
Subject: Re: [RFC PATCH 1/3] veth: implement support for set_channel ethtool
 op

On Fri,  9 Jul 2021 11:39:48 +0200 Paolo Abeni wrote:
> +	/* accept changes only on rx/tx */
> +	if (ch->combined_count != min(dev->real_num_rx_queues, dev->real_num_tx_queues))
> +		return -EINVAL;

Ah damn, I must have missed the get_channels being added. I believe the
correct interpretation of the params is rx means NAPI with just Rx
queue(s), tx NAPI with just Tx queue(s) and combined has both.
IOW combined != min(rx, tx).
Instead real_rx = combined + rx; real_tx = combined + tx.
Can we still change this?

> +	/* respect contraint posed at device creation time */
> +	if (ch->rx_count > dev->num_rx_queues || ch->tx_count > dev->num_tx_queues)
> +		return -EINVAL;

Could you lift this check into ethtool core?

> +	if (!ch->rx_count || !ch->tx_count)
> +		return -EINVAL;

You wouldn't need this with the right interpretation of combined :(

> +	/* avoid braking XDP, if that is enabled */
> +	if (priv->_xdp_prog && ch->rx_count < priv->peer->real_num_tx_queues)
> +		return -EINVAL;
> +
> +	peer_priv = netdev_priv(priv->peer);
> +	if (peer_priv->_xdp_prog && ch->tx_count > priv->peer->real_num_rx_queues)
> +		return -EINVAL;
> +
> +	if (netif_running(dev))
> +		veth_close(dev);
> +
> +	priv->num_tx_queues = ch->tx_count;
> +	priv->num_rx_queues = ch->rx_count;
> +
> +	if (netif_running(dev))
> +		veth_open(dev);