linux-kernel - Re: [RESEND PATCH v3 12/12] usb: misc: usbtest: update to use the usb_control_msg

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Message-ID: <YBGcJb5YtCtGjPtW@hovoldconsulting.com>
Date:   Wed, 27 Jan 2021 18:00:21 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Anant Thazhemadam <anant.thazhemadam@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Bixuan Cui <cuibixuan@...wei.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Zqiang <qiang.zhang@...driver.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v3 12/12] usb: misc: usbtest: update to use the
 usb_control_msg_{send|recv}() API

On Wed, Jan 27, 2021 at 05:42:47PM +0530, Anant Thazhemadam wrote:
> The newer usb_control_msg_{send|recv}() API are an improvement on the
> existing usb_control_msg() as it ensures that a short read/write is treated
> as an error, data can be used off the stack, and raw usb pipes need not be
> created in the calling functions.
> For this reason, instances of usb_control_msg() have been replaced with
> usb_control_msg_{recv|send}() and the return value checking conditions have
> also been modified appropriately.
> 
> Signed-off-by: Anant Thazhemadam <anant.thazhemadam@...il.com>
> ---
> Resending this patch since the subject line for the initial submission 
> (sent as a part of the patch series) wasn't set correctly.
> 
>  drivers/usb/misc/usbtest.c | 69 ++++++++++++++++----------------------
>  1 file changed, 29 insertions(+), 40 deletions(-)
> 
> diff --git a/drivers/usb/misc/usbtest.c b/drivers/usb/misc/usbtest.c
> index 150090ee4ec1..4337eff2a749 100644
> --- a/drivers/usb/misc/usbtest.c
> +++ b/drivers/usb/misc/usbtest.c
> @@ -672,19 +672,15 @@ static int get_altsetting(struct usbtest_dev *dev)
>  	struct usb_device	*udev = interface_to_usbdev(iface);
>  	int			retval;
>  
> -	retval = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
> -			USB_REQ_GET_INTERFACE, USB_DIR_IN|USB_RECIP_INTERFACE,
> -			0, iface->altsetting[0].desc.bInterfaceNumber,
> -			dev->buf, 1, USB_CTRL_GET_TIMEOUT);
> -	switch (retval) {
> -	case 1:
> -		return dev->buf[0];
> -	case 0:
> -		retval = -ERANGE;
> -		fallthrough;
> -	default:
> +	retval = usb_control_msg_recv(udev, 0, USB_REQ_GET_INTERFACE,
> +				      USB_DIR_IN|USB_RECIP_INTERFACE,
> +				      0, iface->altsetting[0].desc.bInterfaceNumber,
> +				      dev->buf, 1, USB_CTRL_GET_TIMEOUT, GFP_KERNEL);
> +
> +	if (retval < 0)
>  		return retval;

This changes the return value for short reads. Maybe not an issue, but
since this a test driver and the value is propagated to user space it is
not clear cut.

> -	}
> +
> +	return dev->buf[0];
>  }
>  
>  static int set_altsetting(struct usbtest_dev *dev, int alternate)
> @@ -872,14 +868,15 @@ static int ch9_postconfig(struct usbtest_dev *dev)
>  		 * ... although some cheap devices (like one TI Hub I've got)
>  		 * won't return config descriptors except before set_config.
>  		 */
> -		retval = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
> -				USB_REQ_GET_CONFIGURATION,
> -				USB_DIR_IN | USB_RECIP_DEVICE,
> -				0, 0, dev->buf, 1, USB_CTRL_GET_TIMEOUT);
> -		if (retval != 1 || dev->buf[0] != expected) {
> +		retval = usb_control_msg_recv(udev, 0, USB_REQ_GET_CONFIGURATION,
> +					      USB_DIR_IN | USB_RECIP_DEVICE,  0,
> +					      0, dev->buf, 1, USB_CTRL_GET_TIMEOUT,
> +					      GFP_KERNEL);
> +
> +		if (retval != 0 || dev->buf[0] != expected) {
>  			dev_err(&iface->dev, "get config --> %d %d (1 %d)\n",
>  				retval, dev->buf[0], expected);
> -			return (retval < 0) ? retval : -EDOM;
> +			return retval;

Same here (but different error, so probably not an issue in either
place).

> @@ -1845,30 +1842,22 @@ static int ctrl_out(struct usbtest_dev *dev,
>  		/* write patterned data */
>  		for (j = 0; j < len; j++)
>  			buf[j] = (u8)(i + j);
> -		retval = usb_control_msg(udev, usb_sndctrlpipe(udev, 0),
> -				0x5b, USB_DIR_OUT|USB_TYPE_VENDOR,
> -				0, 0, buf, len, USB_CTRL_SET_TIMEOUT);
> -		if (retval != len) {
> +		retval = usb_control_msg_send(udev, 0, 0x5b,
> +					      USB_DIR_OUT | USB_TYPE_VENDOR, 0,
> +					      0, buf, len, USB_CTRL_SET_TIMEOUT,
> +					      GFP_KERNEL);

This introduces a redundant allocation and memcpy() for every iteration
for the buffer which is already DMA-able. So this looks like a bad fit
for the new helper.

> +		if (retval < 0) {
>  			what = "write";
> -			if (retval >= 0) {
> -				ERROR(dev, "ctrl_out, wlen %d (expected %d)\n",
> -						retval, len);
> -				retval = -EBADMSG;
> -			}

You could drop this redundant short write test though if you want.

>  			break;
>  		}
>  
>  		/* read it back -- assuming nothing intervened!!  */
> -		retval = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
> -				0x5c, USB_DIR_IN|USB_TYPE_VENDOR,
> -				0, 0, buf, len, USB_CTRL_GET_TIMEOUT);
> -		if (retval != len) {
> +		retval = usb_control_msg_recv(udev, 0,
> +					      0x5c, USB_DIR_IN|USB_TYPE_VENDOR,
> +					      0, 0, buf, len, USB_CTRL_GET_TIMEOUT,
> +					      GFP_KERNEL);
> +		if (retval < 0) {
>  			what = "read";
> -			if (retval >= 0) {
> -				ERROR(dev, "ctrl_out, rlen %d (expected %d)\n",
> -						retval, len);
> -				retval = -EBADMSG;
> -			}

Same here; the buffer is already DMA-able and you remove the error
message, which someone using a test driver like this may want to see.

Probably better left as is.

>  			break;
>  		}

Johan