linux-kernel - Re: [PATCH v11 04/17]Add a function make external buffer owner to query capability.

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Date:	Mon, 27 Sep 2010 14:45:49 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	xiaohui.xin@...el.com
Cc:	netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu, davem@...emloft.net,
	herbert@...dor.hengli.com.au, jdike@...ux.intel.com
Subject: Re: [PATCH v11 04/17]Add a function make external buffer owner to
 query capability.

On Sat, 2010-09-25 at 12:27 +0800, xiaohui.xin@...el.com wrote:
[...]
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 264137f..636f11b 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2468,6 +2468,55 @@ void netif_nit_deliver(struct sk_buff *skb)
>  	rcu_read_unlock();
>  }
>  
> +/* To support meidate passthru(zero-copy) with NIC driver,
> + * we'd better query NIC driver for the capability it can
> + * provide, especially for packet split mode, now we only
> + * query for the header size, and the payload a descriptor
> + * may carry. If a driver does not use the API to export,
> + * then we may try to use a default value, currently,
> + * we use the default value from an IGB driver. Now,
> + * it's only called by mpassthru device.
> + */
> +#if defined(CONFIG_MEDIATE_PASSTHRU) || defined(CONFIG_MEDIATE_PASSTHRU_MODULE)
> +int netdev_mp_port_prep(struct net_device *dev,
> +		struct mpassthru_port *port)
> +{
> +	int rc;
> +	int npages, data_len;
> +	const struct net_device_ops *ops = dev->netdev_ops;
> +
> +	if (ops->ndo_mp_port_prep) {
> +		rc = ops->ndo_mp_port_prep(dev, port);
> +		if (rc)
> +			return rc;
> +	} else {
> +		/* If the NIC driver did not report this,
> +		 * then we try to use default value.
> +		 */
> +		port->hdr_len = 128;
> +		port->data_len = 2048;
> +		port->npages = 1;
> +	}
[...]

Is it really necessary to have a default?

Also have you considered an API for changing the header/data split?

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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