linux-kernel - Re: [PATCH v2] usb: gadget: ether: Allow changing the MTU

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Date:	Fri, 11 Dec 2015 11:47:18 +0100
From:	Mike Looijmans <mike.looijmans@...ic.nl>
To:	<linux-usb@...r.kernel.org>
CC:	<balbi@...com>, <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: gadget: ether: Allow changing the MTU

Just a "ping" reminder, I'd like to inquire about the status of this patch...

On 30-11-15 12:18, Mike Looijmans wrote:
> The gadget ethernet driver supports changing the MTU, but only allows this
> when the USB cable is removed. The comment indicates that this is because
> the "peer won't know". Even if the network link is still down and only the
> USB link is established, the driver won't allow the change.
>
> Other network interfaces allow changing the MTU any time, and don't force
> the link to be disabled. This makes perfect sense, because in order to be
> able to negotiate the MTU, the link needs to be up.
>
> Remove the restriction so that it is now actually possible to change the
> MTU (e.g. using "ifconfig usb0 mtu 15000") without having to manually pull
> the plug or change the driver's default setting.
>
> This is especially important after commit bba787a860fa
> ("usb: gadget: ether: Allow jumbo frames")
>
> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
> ---
> v2: Fix commit reference (checkpatch) and unused variable 'dev' (kbuild test robot)
>
>   drivers/usb/gadget/function/u_ether.c | 18 ++++--------------
>   1 file changed, 4 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
> index 6554322..637809e 100644
> --- a/drivers/usb/gadget/function/u_ether.c
> +++ b/drivers/usb/gadget/function/u_ether.c
> @@ -143,21 +143,11 @@ static inline int qlen(struct usb_gadget *gadget, unsigned qmult)
>
>   static int ueth_change_mtu(struct net_device *net, int new_mtu)
>   {
> -	struct eth_dev	*dev = netdev_priv(net);
> -	unsigned long	flags;
> -	int		status = 0;
> +	if (new_mtu <= ETH_HLEN || new_mtu > GETHER_MAX_ETH_FRAME_LEN)
> +		return -ERANGE;
> +	net->mtu = new_mtu;
>
> -	/* don't change MTU on "live" link (peer won't know) */
> -	spin_lock_irqsave(&dev->lock, flags);
> -	if (dev->port_usb)
> -		status = -EBUSY;
> -	else if (new_mtu <= ETH_HLEN || new_mtu > GETHER_MAX_ETH_FRAME_LEN)
> -		status = -ERANGE;
> -	else
> -		net->mtu = new_mtu;
> -	spin_unlock_irqrestore(&dev->lock, flags);
> -
> -	return status;
> +	return 0;
>   }
>
>   static void eth_get_drvinfo(struct net_device *net, struct ethtool_drvinfo *p)
>



Kind regards,

Mike Looijmans
System Expert

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