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Date: Tue, 20 Sep 2016 15:11:52 +0800
From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: "Kavanagh, Mark B" <mark.b.kavanagh@intel.com>
Cc: "'Dey, Souvik'" <sodey@sonusnet.com>, "dev@dpdk.org" <dev@dpdk.org>,
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Subject: Re: [dpdk-dev] [PATCH v4]net/virtio: add mtu set in virtio
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On Wed, Sep 14, 2016 at 12:15:37PM +0000, Kavanagh, Mark B wrote:
> >
> >>+{
> >>+       struct rte_eth_dev_info dev_info;
> >>+       uint32_t ether_hdr_len = ETHER_HDR_LEN + ETHER_CRC_LEN +
> >>+VLAN_TAG_LEN;
> >>+       uint32_t frame_size = mtu + ether_hdr_len;
> >>+
> >>+       virtio_dev_info_get(dev, &dev_info);
> >>+
> >>+       if (mtu < dev_info.min_rx_bufsize || frame_size >
> >>+dev_info.max_rx_pktlen) {
> >
> >It's not clear to me whether 'mtu' in this case should be compared with ETHER_MIN_MTU, as per
> >other DPDK drivers, or alternatively whether 'frame_size' should be compared with
> >dev_info.min_rx_bufsize.
> >Any thoughts?
> >[Dey, Souvik] I am not sure why virtio min_rx_bufsize is less than ETHER_MIN_MTU, i think it
> >will be good to have the  compare statement as
> >If(frame_size < ETHER_MIN_MTU || frame_size > dev_info.max_rx_pktlen) , then error. What do
> >you suggest ?
> 
> Again, this all depends on what 'mtu' means in this context.
> 
> Since you mentioned previously that it relates to the packet (i.e. L3) length, and not the frame (i.e. L2) length, I would suggest that the comparison should be:
> 
> 	if (mtu < ETHER_MIN_MTU || frame_size > dev_info.max_rx_pktlen)
> 
> Yuanhan, any thoughts on this?

I think you are right. At least, that's how the ixgbe PMD driver code
looks like.

	--yliu