Re: [dpdk-dev] [PATCH v1] add mtu set in virtio

["Dey, Souvik" <sodey@sonusnet.com>]

Hi ,
	Currently as you have mentioned, I have changed the code to:
static int 
 virtio_mtu_set(struct rte_eth_dev *dev, uint16_t mtu) 
 {
    struct virtio_hw *hw = dev->data->dev_private;
-   if (unlikely(mtu < (uint32_t)hw->vtnet_hdr_size + ETHER_HDR_LEN)) {
-       return -1;
+   if (unlikely(mtu < VIRTIO_MIN_RX_BUFSIZE || mtu > VIRTIO_MAX_RX_PKTLEN)) {
+	   PMD_INIT_LOG(ERR,"Mtu should be between 64 and 9728."
+       return -EINVAL;
    }
    return 0;
 }

Yes, we should support till 64K as the kernel does , but I need to go through the changes and test it properly before submitting it for review. Moreover I was thinking with the changes in the mtu, we should also support multi-segment buffers in kni. What do you suggest ?

--
Regards,
Souvik

-----Original Message-----
From: Stephen Hemminger [mailto:stephen@networkplumber.org] 
Sent: Saturday, August 27, 2016 8:16 PM
To: Dey, Souvik <sodey@sonusnet.com>
Cc: huawei.xie@intel.com; yuanhan.liu@linux.intel.com; dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v1] add mtu set in virtio

On Fri, 26 Aug 2016 20:54:28 -0400
souvikdey33 <sodey@sonusnet.com> wrote:

> This functionality is required mostly in the cloud infrastructure.
> For example, if we use gre or vxlan network between compute and 
> controller, then we should not use 1500 mtu in the guest as with 
> encapsulation the sixe of the packet will be more and will get dropped 
> in the infrastructure. So, in that case we should honor the mtu size 
> sent by the dhcp server and configure the same on the virtual 
> interfaces in the guest. This will also keep a consistent mtu through 
> out the infrastructure.
> 
> souvikdey33 (1):
>   Signed-off-by: Souvik Dey <sodey@sonusnet.com>
> 
>  drivers/net/virtio/virtio_ethdev.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 

Thanks for the patch, it is a good step forward but it looks like more code is needed to do this safely. At a minimum, need to check that MTU is not greater than VIRTIO_MAX_RX_PKTLEN.
And error return should be negative errno not -1.

Something like:
   if (mtu < VIRTIO_MIN_MTU || mtu > VIRTIO_MAX_RX_PKTLEN)
	return -EINVAL;

Looking at Linux driver, it allows MTU of up to 64K, yet DPDK only allows 9728.  That should probably be fixed.