linux-kernel - Re: [PATCH 4/4] cp210x: Expose the part number in sysfs

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Date:	Fri, 24 Jul 2015 11:17:55 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Petr Tesarik <ptesarik@...e.com>
Cc:	Johan Hovold <johan@...nel.org>,
	"open list:USB SERIAL SUBSYSTEM" <linux-usb@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	Petr Tesarik <ptesarik@...e.cz>
Subject: Re: [PATCH 4/4] cp210x: Expose the part number in sysfs

On Fri, Jul 24, 2015 at 08:48:11AM +0200, Petr Tesarik wrote:
> From: Petr Tesarik <ptesarik@...e.cz>
> 
> Make it possible to read the cp210x part number from userspace by making
> it a sysfs attribute.
> 
> Signed-off-by: Petr Tesarik <ptesarik@...e.com>

All sysfs files need to be documented in Documentation/ABI/

> ---
>  drivers/usb/serial/cp210x.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> index dbfc722..66de350 100644
> --- a/drivers/usb/serial/cp210x.c
> +++ b/drivers/usb/serial/cp210x.c
> @@ -871,11 +871,24 @@ static void cp210x_break_ctl(struct tty_struct *tty, int break_state)
>  	cp210x_set_config(port, CP210X_SET_BREAK, &state, 2);
>  }
>  
> +static ssize_t part_number_show(struct device *dev,
> +				struct device_attribute *attr, char *buf)
> +{
> +	struct usb_interface *intf = to_usb_interface(dev);
> +	struct usb_serial *serial = usb_get_intfdata(intf);
> +	struct cp210x_serial_private *spriv = usb_get_serial_data(serial);
> +
> +	return sprintf(buf, "%i\n", spriv->bPartNumber);
> +}
> +
> +static DEVICE_ATTR_RO(part_number);
> +
>  static int cp210x_startup(struct usb_serial *serial)
>  {
>  	struct usb_host_interface *cur_altsetting;
>  	struct cp210x_serial_private *spriv;
>  	unsigned int partnum;
> +	int result;
>  
>  	spriv = kzalloc(sizeof(*spriv), GFP_KERNEL);
>  	if (!spriv)
> @@ -892,13 +905,19 @@ static int cp210x_startup(struct usb_serial *serial)
>  			   &partnum, 1, USB_CTRL_GET_TIMEOUT);
>  	spriv->bPartNumber = partnum & 0xFF;
>  
> -	return 0;
> +	result = device_create_file(&serial->interface->dev,
> +				    &dev_attr_part_number);

You just raced with userspace, it will not properly see this attribute
:(

Please never use device_create_file, use an attribute group assigned to
the tty device.  Not the USB interface, that is only for USB interface
"things".

thanks,

greg k-h
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