linux-kernel - Re: [PATCH 08/16 v2] pramfs: headers

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Date:	Mon, 08 Nov 2010 09:09:17 +1300
From:	Ryan Mallon <ryan@...ewatersys.com>
To:	Marco Stornelli <marco.stornelli@...il.com>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Embedded <linux-embedded@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Tim Bird <tim.bird@...sony.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 08/16 v2] pramfs: headers

On 11/06/2010 09:58 PM, Marco Stornelli wrote:
> From: Marco Stornelli <marco.stornelli@...il.com>
> 
> Definitions for the PRAMFS filesystem.
> 
> Signed-off-by: Marco Stornelli <marco.stornelli@...il.com>
> ---
> diff -Nurp linux-2.6.36-orig/fs/pramfs/pram.h linux-2.6.36/fs/pramfs/pram.h
> --- linux-2.6.36-orig/fs/pramfs/pram.h	1970-01-01 01:00:00.000000000 +0100
> +++ linux-2.6.36/fs/pramfs/pram.h	2010-10-30 12:02:45.000000000 +0200
> @@ -0,0 +1,317 @@

> +/*
> + * Structure of the super block in PRAMFS
> + */
> +struct pram_super_block {
> +	__be16	s_sum;          /* checksum of this sb, including padding */
> +	__be64	s_size;         /* total size of fs in bytes */
> +	__be32	s_blocksize;    /* blocksize in bytes */
> +	__be32	s_inodes_count;	/* total inodes count (used or free) */
> +	__be32	s_free_inodes_count;/* free inodes count */
> +	__be32	s_free_inode_hint;  /* start hint for locating free inodes */
> +	__be32	s_blocks_count;	/* total data blocks count (used or free) */
> +	__be32	s_free_blocks_count;/* free data blocks count */
> +	__be32	s_free_blocknr_hint;/* free data blocks count */
> +	__be64	s_bitmap_start; /* data block in-use bitmap location */
> +	__be32	s_bitmap_blocks;/* size of bitmap in number of blocks */
> +	__be32	s_mtime;	/* Mount time */
> +	__be32	s_wtime;	/* Write time */
> +	__be16	s_magic;	/* Magic signature */
> +	char	s_volume_name[16]; /* volume name */
> +};

Is there a particular reason to use big endian types for the data
structures? On a little endian machine you will end up converting values
everywhere. I assume that you don't expect the machine to change
endianess between reboots :-). If this is for generating/reading
filesystems from userspace, wouldn't it be better to have the userspace
tools specify the target endianess and do the conversions there?

~Ryan

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