linux-ext4 - Re: [RFC][PATCH] Set JBD2_FEATURE_INCOMPAT_64BIT on filesystems larger than 32-bit blocks (take 2).

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Date:	Tue, 5 Jun 2007 08:49:37 -0500
From:	"Jose R. Santos" <jrs@...ibm.com>
To:	Laurent Vivier <Laurent.Vivier@...l.net>
Cc:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>, cmm@...ibm.com,
	Andreas Dilger <adilger@...sterfs.com>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [RFC][PATCH] Set JBD2_FEATURE_INCOMPAT_64BIT on filesystems
 larger than 32-bit blocks (take 2).

On Tue, 05 Jun 2007 15:26:53 +0200
Laurent Vivier <Laurent.Vivier@...l.net> wrote:

> Dave Kleikamp wrote:
> > Jose is right.  The endian conversion is unnecessary.
> > 
> > Shaggy
> 
> But by using le32_to_cpu(es->s_blocks_count_hi) you explicitly mark the variable
> as a little-endian.
> So if someone reads the code, he knows this is a little-endian value and this
> allows to avoid errors if later variable must be tested for other value than 0.
> 
> For instance, you have :
> 
> if(es->s_blocks_count_hi)
> 
> and later the value should be compared to 10, how do you know easily you should use:
> 
> if (le32_to_cpu(es->s_blocks_count_hi) == 10)
> 
> instead of
> 
> if(es->s_blocks_count_hi == 10)
> 
> I think writing like Mingming asks should allow to avoid errors later.
> 
> (and code becomes really self-explicit...)
> 
> Regards,
> Laurent

Hi Laurent,

In this particular case though, the value of s_blocks_count_hi should not be uses on its own.  The correct way would be to use ext4_blocks_count() which already does the endian conversion.  If you think the code could confuse people as to how to access the data in s_blocks_count_hi, wouldn't hiding it through the use of a macro make more sense than doing an unnecessary endian conversion?

-JRS
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