Re: [PATCH v5] fs: FAT: Add support for DOS 1.x formatted volumes

[OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>]

Conrad Meyer <cse.cem@gmail.com> writes:

> +	sbi->sec_per_clus = fdefaults->sec_per_clus;
> +	sbi->cluster_size = sb->s_blocksize * sbi->sec_per_clus;
> +	sbi->cluster_bits = ffs(sbi->cluster_size) - 1;
> +	sbi->fats = 2;
> +	sbi->fat_start = 1;
> +	sbi->fat_length = fdefaults->fat_length;
> +
> +	sbi->dir_per_block = sb->s_blocksize / sizeof(struct msdos_dir_entry);
> +	sbi->dir_per_block_bits = ffs(sbi->dir_per_block) - 1;
> +	sbi->dir_start = sbi->fat_start + sbi->fats * sbi->fat_length;
> +	sbi->dir_entries = fdefaults->dir_entries;
> +
> +	rootdir_sectors = sbi->dir_entries
> +		* sizeof(struct msdos_dir_entry) / sb->s_blocksize;
> +	sbi->data_start = sbi->dir_start + rootdir_sectors;
> +	total_sectors = fdefaults->nr_sectors;
> +	total_clusters = (total_sectors - sbi->data_start) / sbi->sec_per_clus;
> +	sbi->fat_bits = (total_clusters > MAX_FAT12) ? 16 : 12;
> +
> +	/* some OSes set FAT_STATE_DIRTY and clean it on unmount. */
> +	sbi->dirty = b->fat16.state & FAT_STATE_DIRTY;
> +
> +	/* check that FAT table does not overflow */
> +	fat_clusters = calc_fat_clusters(sb);
> +	total_clusters = min(total_clusters, fat_clusters - FAT_START_ENT);

Ah, you meant this duplicated one.

Let's use structure like fat_boot_sector (but more cpu friendly) on
stack or something, instead of modify bh (BPB). Modifying bh in bdev is
visible via /dev/foo, this is why I want to avoid to modify.

With this, we can share almost all codes on both of read_bpb() and
static_bpb(), and avoids to modify bdev buffer? And those 2 helpers only
has small chunk of code, and provide the required parameters?

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>