Re: [PATCH v3] virtio-net: Add initial MTU advice feature

[Michael S. Tsirkin]

On Fri, Jun 03, 2016 at 04:57:12PM -0400, Aaron Conole wrote:
> This commit adds the feature bit and associated mtu device entry for the
> virtio network device.  When a virtio device comes up, it checks the
> feature bit for the VIRTIO_NET_F_MTU feature.  If such feature bit is
> enabled, the driver will read the advised MTU and use it as the initial
> value.
> 
> Signed-off-by: Aaron Conole 
> ---
> v2->v3:
> * Added a check for the MTU, and a bit clear for it being out of range.
> 
>  drivers/net/virtio_net.c| 10 ++
>  include/uapi/linux/virtio_net.h |  3 +++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e0638e5..192f321 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1780,6 +1780,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>   struct net_device *dev;
>   struct virtnet_info *vi;
>   u16 max_queue_pairs;
> + int mtu;
>  
>   if (!vdev->config->get) {
>   dev_err(>dev, "%s failure: config access disabled\n",
> @@ -1896,6 +1897,14 @@ static int virtnet_probe(struct virtio_device *vdev)
>   if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
>   vi->has_cvq = true;
>  
> + if (virtio_has_feature(vdev, VIRTIO_NET_F_MTU)) {
> + mtu = virtio_cread16(vdev,
> +  offsetof(struct virtio_net_config,
> +   mtu));
> + if (virtnet_change_mtu(dev, mtu))
> + __virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
> + }
> +
>   if (vi->any_header_sg)
>   dev->needed_headroom = vi->hdr_len;
>  
> @@ -2067,6 +2076,7 @@ static unsigned int features[] = {
>   VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ,
>   VIRTIO_NET_F_CTRL_MAC_ADDR,
>   VIRTIO_F_ANY_LAYOUT,
> + VIRTIO_NET_F_MTU,
>  };
>  
>  static struct virtio_driver virtio_net_driver = {
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index ec32293..1ab4ea6 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -55,6 +55,7 @@
>  #define VIRTIO_NET_F_MQ  22  /* Device supports Receive Flow
>* Steering */
>  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23/* Set MAC address */
> +#define VIRTIO_NET_F_MTU 25  /* Initial MTU advice */
>  
>  #ifndef VIRTIO_NET_NO_LEGACY
>  #define VIRTIO_NET_F_GSO 6   /* Host handles pkts w/ any GSO type */


Oops I just notices this conflicts with virtio spec which says
devices must only use features up to 24.
Please post a follow-up patch changing this to bit 3.


> @@ -73,6 +74,8 @@ struct virtio_net_config {
>* Legal values are between 1 and 0x8000
>*/
>   __u16 max_virtqueue_pairs;
> + /* Default maximum transmit unit advice */
> + __u16 mtu;
>  } __attribute__((packed));
>  
>  /*
> -- 
> 2.5.5
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Re: [PATCH v3] virtio-net: Add initial MTU advice feature

[David Miller]

From: Aaron Conole 
Date: Fri,  3 Jun 2016 16:57:12 -0400

> This commit adds the feature bit and associated mtu device entry for the
> virtio network device.  When a virtio device comes up, it checks the
> feature bit for the VIRTIO_NET_F_MTU feature.  If such feature bit is
> enabled, the driver will read the advised MTU and use it as the initial
> value.
> 
> Signed-off-by: Aaron Conole 

Applied, thanks.
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[PATCH v3] virtio-net: Add initial MTU advice feature

[Aaron Conole]

This commit adds the feature bit and associated mtu device entry for the
virtio network device.  When a virtio device comes up, it checks the
feature bit for the VIRTIO_NET_F_MTU feature.  If such feature bit is
enabled, the driver will read the advised MTU and use it as the initial
value.

Signed-off-by: Aaron Conole 
---
v2->v3:
* Added a check for the MTU, and a bit clear for it being out of range.

 drivers/net/virtio_net.c| 10 ++
 include/uapi/linux/virtio_net.h |  3 +++
 2 files changed, 13 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index e0638e5..192f321 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1780,6 +1780,7 @@ static int virtnet_probe(struct virtio_device *vdev)
struct net_device *dev;
struct virtnet_info *vi;
u16 max_queue_pairs;
+   int mtu;
 
if (!vdev->config->get) {
dev_err(>dev, "%s failure: config access disabled\n",
@@ -1896,6 +1897,14 @@ static int virtnet_probe(struct virtio_device *vdev)
if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
vi->has_cvq = true;
 
+   if (virtio_has_feature(vdev, VIRTIO_NET_F_MTU)) {
+   mtu = virtio_cread16(vdev,
+offsetof(struct virtio_net_config,
+ mtu));
+   if (virtnet_change_mtu(dev, mtu))
+   __virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
+   }
+
if (vi->any_header_sg)
dev->needed_headroom = vi->hdr_len;
 
@@ -2067,6 +2076,7 @@ static unsigned int features[] = {
VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ,
VIRTIO_NET_F_CTRL_MAC_ADDR,
VIRTIO_F_ANY_LAYOUT,
+   VIRTIO_NET_F_MTU,
 };
 
 static struct virtio_driver virtio_net_driver = {
diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index ec32293..1ab4ea6 100644
--- a/include/uapi/linux/virtio_net.h
+++ b/include/uapi/linux/virtio_net.h
@@ -55,6 +55,7 @@
 #define VIRTIO_NET_F_MQ22  /* Device supports Receive Flow
 * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23  /* Set MAC address */
+#define VIRTIO_NET_F_MTU 25/* Initial MTU advice */
 
 #ifndef VIRTIO_NET_NO_LEGACY
 #define VIRTIO_NET_F_GSO   6   /* Host handles pkts w/ any GSO type */
@@ -73,6 +74,8 @@ struct virtio_net_config {
 * Legal values are between 1 and 0x8000
 */
__u16 max_virtqueue_pairs;
+   /* Default maximum transmit unit advice */
+   __u16 mtu;
 } __attribute__((packed));
 
 /*
-- 
2.5.5

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