[PATCH net-next, v2] hv_netvsc: Add support to set MTU reservation from guest side

[PATCH net-next, v2] hv_netvsc: Add support to set MTU reservation from guest side

[Haiyang Zhang]

When packet encapsulation is in use, the MTU needs to be reduced for
headroom reservation.
The existing code takes the updated MTU value only from the host side.
But vSwitch extensions, such as Open vSwitch, require the flexibility
to change the MTU to different values from within a guest during the
lifecycle of a vNIC, when the encapsulation protocol is changed. The
patch supports this kind of MTU changes.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
---
 drivers/net/hyperv/hyperv_net.h   |    1 +
 drivers/net/hyperv/netvsc_drv.c   |    3 +--
 drivers/net/hyperv/rndis_filter.c |    2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index dd45440..26cd14c 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h
@@ -589,6 +589,7 @@ struct nvsp_message {
 
 
 #define NETVSC_MTU 65536
+#define NETVSC_MTU_MIN 68
 
 #define NETVSC_RECEIVE_BUFFER_SIZE		(1024*1024*16)	/* 16MB */
 #define NETVSC_RECEIVE_BUFFER_SIZE_LEGACY	(1024*1024*15)  /* 15MB */
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 358475e..b855ba9 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -743,8 +743,7 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
 	if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2)
 		limit = NETVSC_MTU - ETH_HLEN;
 
-	/* Hyper-V hosts don't support MTU < ETH_DATA_LEN (1500) */
-	if (mtu < ETH_DATA_LEN || mtu > limit)
+	if (mtu < NETVSC_MTU_MIN || mtu > limit)
 		return -EINVAL;
 
 	nvdev->start_remove = true;
diff --git a/drivers/net/hyperv/rndis_filter.c b/drivers/net/hyperv/rndis_filter.c
index 006c1b8..172824e 100644
--- a/drivers/net/hyperv/rndis_filter.c
+++ b/drivers/net/hyperv/rndis_filter.c
@@ -1053,7 +1053,7 @@ int rndis_filter_device_add(struct hv_device *dev,
 	ret = rndis_filter_query_device(rndis_device,
 					RNDIS_OID_GEN_MAXIMUM_FRAME_SIZE,
 					&mtu, &size);
-	if (ret == 0 && size == sizeof(u32))
+	if (ret == 0 && size == sizeof(u32) && mtu < net_device->ndev->mtu)
 		net_device->ndev->mtu = mtu;
 
 	/* Get the mac address */
-- 
1.7.4.1

Re: [PATCH net-next,v2] hv_netvsc: Add support to set MTU reservation from guest side

[David Miller]

From: Haiyang Zhang <haiyangz@microsoft.com>
Date: Mon,  6 Jul 2015 14:11:37 -0700

> When packet encapsulation is in use, the MTU needs to be reduced for
> headroom reservation.
> The existing code takes the updated MTU value only from the host side.
> But vSwitch extensions, such as Open vSwitch, require the flexibility
> to change the MTU to different values from within a guest during the
> lifecycle of a vNIC, when the encapsulation protocol is changed. The
> patch supports this kind of MTU changes.
> 
> Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>

Applied, thanks.