linux-ext4 - Re: [PATCH] ext4: ext4

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Message-Id: <AEF10200-E1C9-4E43-81E2-7B31B144A062@dilger.ca>
Date:	Thu, 27 Sep 2012 15:29:39 +0200
From:	Andreas Dilger <adilger@...ger.ca>
To:	Carlos Maiolino <cmaiolino@...hat.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: ext4_bread usage audit

On 2012-09-26, at 4:14 PM, Carlos Maiolino wrote:
> In regards to the coding style of if conditionals, I just followed the coding
> style of most places in the code, I also changed some of the if conditionals to
> match the rest of the code. i.e.:
> 
> if(!(bh = ext4_bread())) {
> 	do_something();
> }
> 
> if you take a look at the code, most if conditionals regarding the calls to
> ext4_bread() are in the above coding style. I just followed it, but, I'm not
> against change that to another one, but agree the above looks better and save
> some code lines.

The reason that having assignments in conditionals is bad is that it allows
hard-to-find bugs to be in the code:

        if ((bh == ext4_bread())

and

        if ((bh = ext4_bread())

look very similar to the reader, but the use of extra "()" around the
assignment quiets any compiler warnings about incorrect assignments.
In this specific case you _do_ want the assignment to bh, but in many
other cases you do not:

        if (bh = NULL)

would set bh to NULL instead of comparing it, and is IMHO bad coding style.

Cheers, Andreas





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