Re: [dpdk-dev] [PATCH v1 1/6] ethdev: add min/max MTU to device info

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 2/27/2019 9:45 PM, Ian Stokes wrote:
> From: Stephen Hemminger <stephen@networkplumber.org>
> 
> This addresses the usability issue raised by OVS at DPDK Userspace
> summit. It adds general min/max mtu into device info. For compatiablity,
> and to save space, it fits in a hole in existing structure.
> 
> The initial version sets max mtu to normal Ethernet, it is up to
> PMD to set larger value if it supports Jumbo frames.
> 
> Also remove the deprecation notice introduced in 18.11 regarding this
> change and bump ethdev ABI version.
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> Signed-off-by: Ian Stokes <ian.stokes@intel.com>
> Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>

> @@ -2524,6 +2524,8 @@ rte_eth_dev_info_get(uint16_t port_id, struct rte_eth_dev_info *dev_info)
>  	dev_info->rx_desc_lim = lim;
>  	dev_info->tx_desc_lim = lim;
>  	dev_info->device = dev->device;
> +	dev_info->min_mtu = ETHER_MIN_MTU;
> +	dev_info->max_mtu = UINT16_MAX;

Not only mtu but do you think should we document in 'rte_eth_dev_info_get()'
doxygen documentation, the default values that API sets?

>  
>  	RTE_FUNC_PTR_OR_RET(*dev->dev_ops->dev_infos_get);
>  	(*dev->dev_ops->dev_infos_get)(dev, dev_info);
> @@ -2587,12 +2589,17 @@ int
>  rte_eth_dev_set_mtu(uint16_t port_id, uint16_t mtu)
>  {
>  	int ret;
> +	struct rte_eth_dev_info dev_info;
>  	struct rte_eth_dev *dev;
>  
>  	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
>  	dev = &rte_eth_devices[port_id];
>  	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->mtu_set, -ENOTSUP);
>  
> +	rte_eth_dev_info_get(port_id, &dev_info);

If we rely on 'rte_eth_dev_info_get()', we should add a check if "dev_infos_get"
is supported before calling it, like [1]. Unfortunately 'rte_eth_dev_info_get()'
return type is 'void', so we can't know if the struct has valid values or not
otherwise.
Or perhaps if port doesn't support "dev_infos_get", we can skip the mtu check
instead of returning error.

[1]
RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->dev_infos_get, -ENOTSUP);

> +	if (mtu < dev_info.min_mtu || mtu > dev_info.max_mtu)
> +		return -EINVAL;
> +

Should we document this behavior change in the function comment in header file?
Update when -EINVAL returned, etc..