Re: [PATCH 1/2] Make cramfs little endian only

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 4 Dec 2007 13:01:26 +0100
Andi Drebes <lists-receive@programmierforen.de> wrote:

> The following patch makes cramfs little endian only. When trying to mount a big endian image,
> an error message is produced.
> 
> The changes were tested on the following types of machines:
> An i386 compatible box (little endian)
> UltraSparc IIi (big endian)
> 
> Signed-off-by: Andi Drebes <andi@programmierforen.de>
> ---
>  inode.c |  163 +++++++++++++++++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 136 insertions(+), 27 deletions(-)
> 
> diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
> index 350680f..3fbf567 100644
> --- a/fs/cramfs/inode.c
> +++ b/fs/cramfs/inode.c
> @@ -4,6 +4,10 @@
>   * Copyright (C) 1999 Linus Torvalds.
>   *
>   * This file is released under the GPL.
> + *
> + * Changelog:
> + *	11/07 - Andi Drebes <andi@programmierforen.de>
> + *	Made cramfs little endian only.
>   */
>  
>  /*
> @@ -40,6 +44,95 @@ static DEFINE_MUTEX(read_mutex);
>  #define CRAMINO(x)	(((x)->offset && (x)->size)?(x)->offset<<2:1)
>  #define OFFSET(x)	((x)->i_ino)
>  
> +#ifdef __BIG_ENDIAN
> +/* Converts a cramfs_info from little endian to big endian. */
> +static inline void cramfs_convert_info_letobe(struct cramfs_info* info)
> +{
> +	 info->crc = swab32(info->crc);
> +	 info->edition = swab32(info->edition);
> +	 info->blocks = swab32(info->blocks);
> +	 info->files = swab32(info->files);
> +}
> +
> +/* Converts a cramfs_info from little endian to big endian. */
> +static inline void cramfs_convert_inode_letobe(struct cramfs_inode* inode)
> +{
> +	u8* inode_bytes = (u8*)inode;
> +	u8 old_nloffs[4];
> +
> +	inode->mode = swab16(inode->mode);
> +	inode->uid = swab16(inode->uid);
> +	inode->size = (inode_bytes[6] << 16) | (inode_bytes[5] << 8) | (inode_bytes[4]);

eww.  Is there a nicer way of doing that?

Might be a bit tricky given the weird way in which struct cramfs_inode was
defined.

> +
> +	/* Save the old values of the namelength and the offset */
> +	memcpy(old_nloffs, inode_bytes+8, 4);
> +
> +	/* Convert the namelength and the offset */
> +	inode_bytes[8] = ((old_nloffs[0] & 0x3f) << 2) | ((old_nloffs[3] & 0xc0) >> 6);
> +	inode_bytes[9] = ((old_nloffs[3] & 0x3f) << 2) | ((old_nloffs[2] & 0xc0) >> 6);
> +	inode_bytes[10] = ((old_nloffs[2] & 0x3f) << 2) | ((old_nloffs[1] & 0xc0) >> 6);
> +	inode_bytes[11] = ((old_nloffs[1] & 0x3f) << 2) | ((old_nloffs[0] & 0xc0) >> 6);
> +}
> +
> +/* Converts a cramfs superblock from little endian to big endian. */
> +static inline void cramfs_convert_super_letobe(struct cramfs_super* super)
> +{
> +	super->magic = swab32(super->magic);
> +	super->size = swab32(super->size);
> +	super->flags = swab32(super->flags);
> +	super->future = swab32(super->future);
> +	cramfs_convert_info_letobe(&super->fsid);
> +	cramfs_convert_inode_letobe(&super->root);
> +}

These inlines are not sane.  Just removing those three takes the sparc64
fs/cramfs/inode.o from 6856 bytes of text down to 5668, which is rather a
large difference.

The patch has a number of trivial coding-style errors. 
scripts/checkpatch.pl finds them.