linux-kernel - Re: [PATCH] udf: convert some macros to functions

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Date:	Mon, 7 Jan 2008 12:26:18 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	marcin.slusarz@...il.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ben Fennema <bfennema@...con.csc.calpoly.edu>,
	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH] udf: convert some macros to functions

On Sun, Jan 06, 2008 at 01:44:34AM +0100, marcin.slusarz@...il.com wrote:
> +static struct udf_bitmap *udf_sb_alloc_bitmap(struct super_block *sb, __u32 index)
> +{
> +	struct udf_part_map *map = &UDF_SB(sb)->s_partmaps[index];
> +	int nr_groups = (map->s_partition_len + (sizeof(struct spaceBitmapDesc) << 3) +
> +		(sb->s_blocksize * 8) - 1) / (sb->s_blocksize * 8);
> +	int size = sizeof(struct udf_bitmap) + (sizeof(struct buffer_head *) * nr_groups);
> +	struct udf_bitmap *bitmap;
> +
> +	if (size <= PAGE_SIZE)
> +		bitmap = kmalloc(size, GFP_KERNEL);
> +	else
> +		bitmap = vmalloc(size);
> +	if (bitmap != NULL) {
> +		memset(bitmap, 0x00, size);
> +		bitmap->s_block_bitmap = (struct buffer_head **)(bitmap + 1);
> +		bitmap->s_nr_groups = nr_groups;
> +	} else
> +		udf_error(sb, __FUNCTION__, "Unable to allocate space for bitmap and %d buffer_head pointers", nr_groups);
> +	return bitmap;
> +}

There's some overly long lines here and some odd style, this should look
more like:

static struct udf_bitmap *udf_sb_alloc_bitmap(struct super_block *sb,
		u32 index)
{
	struct udf_part_map *map = &UDF_SB(sb)->s_partmaps[index];
	struct udf_bitmap *bitmap;
	int nr_groups;
	int size;

	nr_groups = (map->s_partition_len +
		(sizeof(struct spaceBitmapDesc) << 3) +
		 (sb->s_blocksize * 8) - 1) /
		(sb->s_blocksize * 8);
	size = sizeof(struct udf_bitmap) +
		(sizeof(struct buffer_head *) * nr_groups);
	if (size <= PAGE_SIZE)
		bitmap = kmalloc(size, GFP_KERNEL);
	else
		bitmap = vmalloc(size);

	if (!bitmap) {
		udf_error(sb, __FUNCTION__,
			  "Unable to allocate space for bitmap "
			  "and %d buffer_head pointers", nr_groups);
		return NULL;
	}

	memset(bitmap, 0, size);
	bitmap->s_block_bitmap = (struct buffer_head **)(bitmap + 1);
	bitmap->s_nr_groups = nr_groups;
	return bitmap;
}

But even that is not quite optimal.  The nr_groups calculation should
probably move to a helper (I suspect it's used elsewhere too anyway),
and instead of using vmalloc for large allocations I'd rather split
the allocation of the bitmap from s->block_bitmap and use individual
smaller allocations.  But that latter part is probably better left
for a separate patch.

But in generally this is a good cleanup and thanks a lot for working
on this filesystem driver.
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