linux-kernel - Re: [PATCH] USB: misplaced parenthesis

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Date:	Tue, 16 Feb 2010 10:52:19 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Roel Kluin <roel.kluin@...il.com>
cc:	Joe Perches <joe@...ches.com>,
	Matthew Dharm <mdharm-usb@...-eyed-alien.net>,
	<linux-usb@...r.kernel.org>,
	<usb-storage@...ts.one-eyed-alien.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] USB: misplaced parenthesis

On Tue, 16 Feb 2010, Roel Kluin wrote:

> > I think it'd be better if you hoisted the set'n'test out of the if()
> 
> ok, I agree.
> 
> > Isn't this the current logic?
> > 
> > 	result = usbat_write_block(us, USBAT_ATA, srb->cmnd, 12,
> > 				   srb->cmnd[0] == GPCMD_BLANK ? 75 : 10, 0);
> > 	result = result != USB_STOR_TRANSPORT_GOOD;
> > 	if (result)
> > 		return result;
> 
> Thanks for your comments, Yes that was the current logic, which I thought
> was wrong, but now I think it could also be obscurely written but right:
> 
> in drivers/usb/storage/transport.h line 100 note the definitions:
> 
> #define USB_STOR_TRANSPORT_GOOD    0   /* Transport good, command good     */
> #define USB_STOR_TRANSPORT_FAILED  1   /* Transport good, command failed   */
> #define USB_STOR_TRANSPORT_NO_SENSE 2  /* Command failed, no auto-sense    */
> #define USB_STOR_TRANSPORT_ERROR   3   /* Transport bad (i.e. device dead) */
> 
> With the current logic usbat_hp8200e_transport() returns TRANSPORT_FAILED,
> even if usbat_write_block() returned TRANSPORT_NO_SENSE or TRANSPORT_ERROR.
> 
> This could be intended, but then the author chose a very obscure way to write:
> 
> 	if (usbat_write_block(us, USBAT_ATA, srb->cmnd, 12,
> 			      srb->cmnd[0] == GPCMD_BLANK ? 75 : 10, 0) !=
> 			      USB_STOR_TRANSPORT_GOOD) 
> 		return USB_STOR_TRANSPORT_FAILED;
> 
> Or was the parenthesis misplaced and should it really be:
> 
> 	result = usbat_write_block(us, USBAT_ATA, srb->cmnd, 12,
> 				   srb->cmnd[0] == GPCMD_BLANK ? 75 : 10, 0);
> 
> 	if (result != USB_STOR_TRANSPORT_GOOD)
>  		return result;
>  
> Maybe someone with the specs/more knowledge of this driver could look into
> this?

It seems pretty clear that your patch was correct and the parens were 
misplaced.  In usb-storage, transport routines like 
usbat_hp8200e_transport() are supposed to return one of the 
USB_STOR_TRANSPORT_* codes, not a Boolean value.

I do agree with Joe that it would be better form to separate the 
function call and the "if" into two statements, as in your second 
version above.  Compare with the code a few lines higher:

        if ( (result = usbat_multiple_write(us, 
                        registers, data, 7)) != USB_STOR_TRANSPORT_GOOD) {
                return result;
        }

The meaning is clear, even though this also unnecessarily squeezes a 
function call and a test into one statement and includes unneeded {}'s.

Alan Stern

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