[PATCH] usb: gadget: ether: Allow changing the MTU

[PATCH] usb: gadget: ether: Allow changing the MTU

[Mike Looijmans]

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@topic.nl>
---
 drivers/usb/gadget/function/u_ether.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
index 6554322..9c60e57 100644
--- a/drivers/usb/gadget/function/u_ether.c
+++ b/drivers/usb/gadget/function/u_ether.c
@@ -144,20 +144,12 @@ 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;
 
-	/* 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);
+	if (new_mtu <= ETH_HLEN || new_mtu > GETHER_MAX_ETH_FRAME_LEN)
+		return -ERANGE;
+	net->mtu = new_mtu;
 
-	return status;
+	return 0;
 }
 
 static void eth_get_drvinfo(struct net_device *net, struct ethtool_drvinfo *p)
-- 
1.9.1

Re: [PATCH] usb: gadget: ether: Allow changing the MTU

[kbuild test robot]

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Hi Mike,

[auto build test WARNING on: balbi-usb/next]
[also build test WARNING on: v4.4-rc3 next-20151127]

url:    https://github.com/0day-ci/linux/commits/Mike-Looijmans/usb-gadget-ether-Allow-changing-the-MTU/20151130-162847
base:   https://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git next
config: i386-randconfig-s1-201548 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All warnings (new ones prefixed by >>):

   drivers/usb/gadget/function/u_ether.c: In function 'ueth_change_mtu':
>> drivers/usb/gadget/function/u_ether.c:146:18: warning: unused variable 'dev' [-Wunused-variable]
     struct eth_dev *dev = netdev_priv(net);
                     ^

vim +/dev +146 drivers/usb/gadget/function/u_ether.c

2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  130  #else
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  131  #define VDBG(dev, fmt, args...) \
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  132  	do { } while (0)
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  133  #endif /* DEBUG */
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  134  
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  135  #define ERROR(dev, fmt, args...) \
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  136  	xprintk(dev , KERN_ERR , fmt , ## args)
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  137  #define INFO(dev, fmt, args...) \
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  138  	xprintk(dev , KERN_INFO , fmt , ## args)
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  139  
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  140  /*-------------------------------------------------------------------------*/
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  141  
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  142  /* NETWORK DRIVER HOOKUP (to the layer above this driver) */
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  143  
ccad637b drivers/usb/gadget/u_ether.c          Stephen Hemminger 2008-11-19  144  static int ueth_change_mtu(struct net_device *net, int new_mtu)
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  145  {
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19 @146  	struct eth_dev	*dev = netdev_priv(net);
1616c4ef drivers/usb/gadget/function/u_ether.c Mike Looijmans    2015-11-30  147  
1616c4ef drivers/usb/gadget/function/u_ether.c Mike Looijmans    2015-11-30  148  	if (new_mtu <= ETH_HLEN || new_mtu > GETHER_MAX_ETH_FRAME_LEN)
1616c4ef drivers/usb/gadget/function/u_ether.c Mike Looijmans    2015-11-30  149  		return -ERANGE;
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  150  	net->mtu = new_mtu;
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  151  
1616c4ef drivers/usb/gadget/function/u_ether.c Mike Looijmans    2015-11-30  152  	return 0;
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  153  }
2b3d942c drivers/usb/gadget/u_ether.c          David Brownell    2008-06-19  154  

:::::: The code at line 146 was first introduced by commit
:::::: 2b3d942c4878084a37991a65e66512c02b8fa2ad usb ethernet gadget: split out network core

:::::: TO: David Brownell <dbrownell@users.sourceforge.net>
:::::: CC: Greg Kroah-Hartman <gregkh@suse.de>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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