Re: [PATCH] fs-private data in struct block_device

[Andrew Morton <akpm@osdl.org>]

Christoph Hellwig <hch@lst.de> wrote:
>
> Al had some critism about a per-blockdev XFS datastructure a while ago
> and so I tried to follow the suggestion in favour of using struct
> block_device directly.  Unfortunately XFS requires a little bit more
> information than what's available in struct block_device, in particular
> whether the blocksize (not sector size) for that devices is identical
> to the page size, and we can't really get that from elsewhere due to
> layering constraints.

Why doesn't `if (bdev->bd_block_size == PAGE_SIZE)' work?

Or sb->s_blocksize?

Generally, redundant info like this is a hassle because it has to be kept
coherent with the thing which it is duplicating.

I suspect I don't understand the problem.

> Nathan Scott scott suggested turning the bd_invalidated fields into a
> flags field where the filesystem uses the so far unused flags for it's
> purposed (similar to struct buffer_head), but I think maybe the variant
> below that just adds a unsigned long for filesystem usage might be more
> useful as it also allows storing a pointer if needed.  Comments?
> 
> 
> --- 1.276/include/linux/fs.h	Mon Dec 29 22:37:20 2003
> +++ edited/include/linux/fs.h	Thu Jan  1 13:42:08 2004
> @@ -353,6 +353,7 @@
>  	int			bd_invalidated;
>  	struct gendisk *	bd_disk;
>  	struct list_head	bd_list;
> +	unsigned long		bd_fspriv; /* file-system private data */
>  };
>  
>  /*

Seems sane.  You'll need to decide whether that field should be operated
upon with atomic ops.  If so, document it.  If not, document its locking,
please.