Re: [Ext2-devel] [RFC] [PATCH] Clean up fs.h union for ext2

Daniel Phillips
2001-12-28T01:52:32Z

Hi Andreas

On December 27, 2001 07:14 pm, Andreas Dilger wrote:
> On Dec 27, 2001 04:21 +0100, Daniel Phillips wrote:
> > The strategy is to abstract all references to the struct inode union through
> > an inline function:
> >
> > static inline struct ext2_inode_info *ext2_i (struct inode *inode)
> > {
> > return &(inode->u.ext2_inode_info);
> > }
> >
> > There is some grist here for the mills of language lawyers here. Note the
> > compilation warning:
> >
> > ialloc.c:336: warning: passing arg 1 of `ext2_i' discards qualifiers from
> > pointer target type
>
> Why not just declare ext2_i like the following? It _should_ work:
>
> static inline struct ext2_inode_info *ext2_i(const struct inode *inode)
> {
> return &(inode->u.ext2_inode_info);
> }

If that's all we do, then we get 'warning: return discards qualifiers from
pointer target type'. Adding an explicit cast gets rid of that:

static inline struct ext2_inode_info *ext2_i (const struct inode *inode)
{
return (struct ext2_inode_info *) &(inode->u.ext2_inode_info);
}

However, then we're lying to the compiler. I wonder how safe that is.

> Minor nit: this is already done for the ext3 code, but it looks like:
>
> #define EXT3_I (&((inode)->u.ext3_i))
>
> We already have the EXT3_SB, so I thought I would be consistent with it:
>
> #define EXT3_SB (&((sb)->u.ext3_sb))
>
> Do people like the inline version better? Either way, I would like to make
> the ext2 and ext3 codes more similar, rather than less.

An upcoming version will use an explicit cast:

return (struct ext2_inode_info *) (inode + 1);

In other words, it doesn't rely on the union, which we're trying to get rid of.
In this case, an inline function provides type saftey and a macro wouldn't. I
also prefer to pass the inode/sb explicitly, rather than having a macro pick it
up from context.

In the superblock patch, the inline will be 'ext2_s'. Al seems comfortable with
this terminology, so...

--
Daniel