Subject: Re: [PATCH] netdev: handle setting transmit queue length on active device.

From: Eric Dumazet <[email-masked]>
Date: Wed, 18 Mar 2009 18:18:44 +0100

Stephen Hemminger a écrit :
> Some virtual devices like VLAN's or bridges by default have not transmit queue.
> In order to do queuing disciplines on these devices a queue must be added
> by setting transmit queue length. The kernel allows doing this at any time, but
> setting the queue length value is not enough. Setting the queue length does
> not create the transmit queue (going from 0 to non-zero) or destroy it
> (setting to zero); the queue is only created (or destroyed) when device
> comes up (or goes down).
> 
> This patch handles this be doing the necessary activations.
> 
> Signed-off-by: Stephen Hemminger <[email-masked]>
> 
> ---
>  include/linux/netdevice.h |    2 ++
>  net/core/dev.c            |   19 +++++++++++++++++--
>  net/core/net-sysfs.c      |    5 ++---
>  net/core/rtnetlink.c      |    2 +-
>  4 files changed, 22 insertions(+), 6 deletions(-)
> 
> --- a/include/linux/netdevice.h	2009-03-17 11:06:40.358479573 -0700
> +++ b/include/linux/netdevice.h	2009-03-17 11:13:55.243604979 -0700
> @@ -1436,6 +1436,8 @@ extern int		dev_change_net_namespace(str
>  extern int		dev_set_mtu(struct net_device *, int);
>  extern int		dev_set_mac_address(struct net_device *,
>  					    struct sockaddr *);
> +extern int		dev_set_tx_queue_len(struct net_device *dev,
> +					     unsigned long len);
>  extern int		dev_hard_start_xmit(struct sk_buff *skb,
>  					    struct net_device *dev,
>  					    struct netdev_queue *txq);
> --- a/net/core/dev.c	2009-03-17 11:05:54.919541341 -0700
> +++ b/net/core/dev.c	2009-03-17 11:16:25.717479320 -0700
> @@ -983,6 +983,22 @@ int dev_set_alias(struct net_device *dev
>  	return len;
>  }
>  
> +/**
> + *
> + *	@dev: device
> + *	@len: limit of frames in transmit queue
> + *
> + *	Set ifalias for a device,

copy/pasted from "dev_set_alias - change ifalias of a device" ? ;)

> + */
> +int dev_set_tx_queue_len(struct net_device *dev, unsigned long len)
> +{

if (dev->tx_queue_len == len)
	return 0;

> +	if (dev->flags & IFF_UP)
> +		dev_deactivate(dev);

So changing txqueuelen will drop frames ?

> +	dev->tx_queue_len = len;
> +	if (dev->flags & IFF_UP)
> +		dev_activate(dev);
> +	return 0;
> +}
>  
>