netdev - Re: Subject: re-submit4 [ANNOUNCEMENT] NET: usb: sierra

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Date:	Thu, 22 Apr 2010 14:15:06 -0700
From:	Dan Williams <dcbw@...hat.com>
To:	Greg KH <greg@...ah.com>
Cc:	Elina Pasheva <epasheva@...rrawireless.com>,
	dbrownell@...rs.sourceforge.net, davem@...emloft.net,
	rfiler@...rrawireless.com, linux-usb@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: Subject: re-submit4 [ANNOUNCEMENT] NET: usb: sierra_net.c
 driver

On Thu, 2010-04-22 at 12:44 -0700, Greg KH wrote:
> On Thu, Apr 22, 2010 at 12:19:33PM -0700, Elina Pasheva wrote:
> > +static void sierra_net_send_cmd(struct usbnet *dev,
> > +		u8 *cmd, int cmdlen, const char * cmd_name)
> > +{
> > +	struct sierra_net_data *priv = sierra_net_get_private(dev);
> > +	int  status;
> > +
> > +	status = usb_control_msg(dev->udev, usb_sndctrlpipe(dev->udev, 0),
> > +			USB_CDC_SEND_ENCAPSULATED_COMMAND,
> > +			USB_DIR_OUT|USB_TYPE_CLASS|USB_RECIP_INTERFACE,	0,
> > +			priv->ifnum, cmd, cmdlen, 0);
> 
> No timeout?
> 
> > +		ifnum = priv->ifnum;
> > +		len = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev, 0),
> > +				USB_CDC_GET_ENCAPSULATED_RESPONSE,
> > +				USB_DIR_IN|USB_TYPE_CLASS|USB_RECIP_INTERFACE,
> > +				0, ifnum, buf, SIERRA_NET_USBCTL_BUF_LEN, 0);
> 
> No timeout?
> 
> > +		if (unlikely(len < 0)) {
> > +			netdev_err(dev->net,
> > +				"usb_control_msg failed, status %d\n", len);
> 
> You don't need "unlikely", this is an extreemly slow path here.
> Also, what happens for a "short read"?  You don't handle that properly.

Is the code doc for usb_unlink_urb() in urb.c the best thing to look at
for how to handle short reads?  I assume that involves checking if the
returned error is -EREMOTEIO and if so, ignoring it?  I spent about an
hour googling and poking around in the kernel sources and couldn't find
much about how to handle short reads.  The only non-host-side driver
that cares about EREMOTEIO is misc/rio500.c, the rest is all under host/
or gadget/.

In the 3 places that this driver calls usb_control_msg(), the codepaths
don't need any special -EREMOTEIO handling.

Dan

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