linux-kernel - Re: [PATCH v2] USB hub_probe: remove ugly goto-into-compound-statement

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Date:   Mon, 7 Nov 2016 10:09:17 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Eugene Korenevsky <ekorenevsky@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Chase Metzger <chasemetzger15@...il.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Oliver Neukum <oneukum@...e.com>, Hans Yang <hansy@...dia.com>
Subject: Re: [PATCH v2] USB hub_probe: remove ugly
 goto-into-compound-statement

On Wed, Nov 02, 2016 at 08:59:44PM +0300, Eugene Korenevsky wrote:
> Rework smelling code (goto inside compound statement). Perhaps this is legacy.
> Anyway such code is not appropriate for Linux kernel.
> 
> Signed-off-by: Eugene Korenevsky <ekorenevsky@...il.com>
> ---
>  drivers/usb/core/hub.c | 24 +++++++++++-------------
>  1 file changed, 11 insertions(+), 13 deletions(-)

What changed from v1?



> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index cbb1467..4081672 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -1802,23 +1802,21 @@ static int hub_probe(struct usb_interface *intf, const struct usb_device_id *id)
>  
>  	/* Some hubs have a subclass of 1, which AFAICT according to the */
>  	/*  specs is not defined, but it works */
> -	if ((desc->desc.bInterfaceSubClass != 0) &&
> -	    (desc->desc.bInterfaceSubClass != 1)) {
> -descriptor_error:
> +
> +	/* Reject in following cases:
> +	 * - Interface subclass is not 0 or 1
> +	 * - Multiple endpoints
> +	 * - Not an interrupt in endpoint
> +	 */
> +	endpoint = &desc->endpoint[0].desc;
> +	if ((desc->desc.bInterfaceSubClass != 0 &&
> +	     desc->desc.bInterfaceSubClass != 1) ||
> +	    desc->desc.bNumEndpoints != 1 ||
> +	    !usb_endpoint_is_int_in(endpoint)) {
>  		dev_err(&intf->dev, "bad descriptor, ignoring hub\n");
>  		return -EIO;
>  	}
>  
> -	/* Multiple endpoints? What kind of mutant ninja-hub is this? */
> -	if (desc->desc.bNumEndpoints != 1)
> -		goto descriptor_error;
> -
> -	endpoint = &desc->endpoint[0].desc;
> -
> -	/* If it's not an interrupt in endpoint, we'd better punt! */
> -	if (!usb_endpoint_is_int_in(endpoint))
> -		goto descriptor_error;
> -

As "horrible" as the original code might be, it's much easier to read
and follow, which is the key thing here, right?  What's so bad about a
goto backwards?

thanks,

greg k-h