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Date: Tue, 29 May 2007 11:00:41 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "Robert P. J. Day" <rpjday@mindspring.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH] FILESYSTEMS:  Delete unused "int dummy[5]" from
 inodes_stat_t.
Message-Id: <20070529110041.49bf57f1.akpm@linux-foundation.org>
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On Tue, 29 May 2007 13:11:07 -0400 (EDT)
"Robert P. J. Day" <rpjday@mindspring.com> wrote:

> 
> Delete the apparently unused array "int dummy[5]" from struct
> inodes_stat_t.
> 
> Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
> 
> ---
> 
>   no idea what that array is for, but no one seems to care about it.
> removal compile-tested on x86 with "make allyesconfig" and nobody
> misses it (unless it's used for padding of some kind).
> 
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 7cf0c54..dec83dd 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -44,7 +44,6 @@ extern int get_max_files(void);
>  struct inodes_stat_t {
>  	int nr_inodes;
>  	int nr_unused;
> -	int dummy[5];
>  };
>  extern struct inodes_stat_t inodes_stat;
> 

kernel/sysctl.c:

	{
		.ctl_name	= FS_STATINODE,
		.procname	= "inode-state",
		.data		= &inodes_stat,
		.maxlen		= 7*sizeof(int),
		.mode		= 0444,
		.proc_handler	= &proc_dointvec,
	},

akpm:/home/akpm> cat /proc/sys/fs/inode-state 
608039  178454  0       0       0       0       0

So it _is_ used: to present those five zeroes.  I think this is for
back-compatibility with some cretaceous-era kernel.