--
Regards,
Souvik

-----Original Message-----
From: Dey, Souvik
Sent: Saturday, October 1, 2016 10:09 AM
To: mark.b.kavanagh@intel.com; yuanhan.liu@linux.intel.com; 
stephen@networkplumber.org; dev@dpdk.org
Subject: RE: [PATCH v7] net/virtio: add set_mtu in virtio

Hi Liu/Stephen/Mark,

I have submitted Version 7 of this patch. Do let me know if this looks proper.

--
Regards,
Souvik

-----Original Message-----
From: Dey, Souvik
Sent: Thursday, September 29, 2016 4:32 PM
To: mark.b.kavanagh@intel.com; yuanhan.liu@linux.intel.com; 
stephen@networkplumber.org; dev@dpdk.org
Cc: Dey, Souvik <redacted>
Subject: [PATCH v7] net/virtio: add set_mtu in virtio


Virtio interfaces do not currently allow the user to specify a 
particular Maximum Transmission Unit (MTU).Consequently, the MTU of 
Virtio interfaces is typically set to the Ethernet default value of 1500.
This is problematic in the case of cloud deployments, in which a 
specific (and potentially non-standard) MTU needs to be set by a DHCP 
server, which needs to be honored by all interfaces across the traffic 
path.To achieve this Virtio interfaces should support setting of MTU.
In case when GRE/VXLAN tunneling is used for internal communication, 
there will be an overhead added by the infrastructure in the packet 
over and above the ETHER MTU of 1518. So to take care of this overhead 
in these cases the DHCP server corrects the L3 MTU to 1454. But since 
virtio interfaces was not having the MTU set functionality that MTU 
sent by the DHCP server was ignored and the instance will still send 
packets with 1500 MTU which after encapsulation will become more than 
1518 and eventually gets dropped in the infrastructure.
By adding an additional 'set_mtu' function to the Virtio driver, we can 
honor the MTU sent by the DHCP server. The dhcp server/controller can 
then leverage this 'set_mtu' functionality to resolve the above 
mentioned issue of packets getting dropped due to incorrect size.


Signed-off-by: Souvik Dey <redacted>

---
Changes in v7:
- Replaced the CRC_LEN with the merge rx buf header length.
- Changed the frame_len max validation to VIRTIO_MAX_RX_PKTLEN.
Changes in v6:
- Description of change corrected
- Corrected the identations
- Corrected the subject line too
- The From line was also not correct
- Re-submitting as the below patch was not proper Changes in v5:
- Fix log message for out-of-bounds MTU parameter in virtio_mtu_set
- Calculate frame size, based on 'mtu' parameter
- Corrected the upper bound and lower bound checks in virtio_mtu_set 
Changes in v4: Incorporated review comments.
Changes in v3: Corrected few style errors as reported by sys-stv.
Changes in v2: Incorporated review comments.

drivers/net/virtio/virtio_ethdev.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/drivers/net/virtio/virtio_ethdev.c 

b/drivers/net/virtio/virtio_ethdev.c
index 423c597..1dbfea6 100644

--- a/drivers/net/virtio/virtio_ethdev.c
+++ b/drivers/net/virtio/virtio_ethdev.c

@@ -653,12 +653,20 @@ virtio_dev_allmulticast_disable(struct rte_eth_dev *dev)
               PMD_INIT_LOG(ERR, "Failed to disable allmulticast");  }

+#define VLAN_TAG_LEN           4    /* 802.3ac tag (not DMA'd) */

+		return -EINVAL;
+	}
+	return 0;
+}

/*
 * dev_ops for virtio, bare necessities for basic operation
 */

@@ -677,7 +685,6 @@ static const struct eth_dev_ops virtio_eth_dev_ops = {

	.allmulticast_enable     = virtio_dev_allmulticast_enable,
	.allmulticast_disable    = virtio_dev_allmulticast_disable,
+	.mtu_set                 = virtio_mtu_set,
	.dev_infos_get           = virtio_dev_info_get,
	.stats_get               = virtio_dev_stats_get,
	.xstats_get              = virtio_dev_xstats_get,
--
2.9.3.windows.1