linux-kernel - Re: ext4: cache all of an extent tree's leaf block upon reading

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Message-ID: <20130905145334.GB23661@thunk.org>
Date:	Thu, 5 Sep 2013 10:53:34 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: ext4: cache all of an extent tree's leaf block upon reading

On Thu, Sep 05, 2013 at 10:37:49AM -0400, Dave Jones wrote:
>  > +void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
>  > +			  ext4_lblk_t len, ext4_fsblk_t pblk,
>  > +			  unsigned int status)
>  > +{
>  > +	struct extent_status *es;
>  > +	struct extent_status newes;
>  > +	ext4_lblk_t end = lblk + len - 1;
>  > +
>  > +	newes.es_lblk = lblk;
>  > +	newes.es_len = len;
>  > +	ext4_es_store_pblock(&newes, pblk);
> 
> 
> ext4_es_store_pblock or's the pblk with the existing contents of the struct member.
> (albeit masked with ES_MASK)
> 
> Should there be a 
> 
> 	newes.es_pblk = 0;
> 
> up there too ?

The next line after ext4_es_store_pblock() is:

        ext4_es_store_status(&newes, status);

This will set remaining ES_WRITTEN | ES_UNWRITTEN... bits.

So the only reason to add a line explicitly setting es_pblk to zero
would be to suppress a warning from some insufficiently smart static
code analysis tool.  I didn't see a warning from gcc, but it's
possible that this is something which is causing Coverity or some
other code scanner heartburn.

Cheers,

					- Ted
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