Re: [PATCH v3 06/11] exfat: add data_start_bytes and exfat_cluster_to_phys() helper

[CharSyam]

Hi, Namjae.

The calculation looks correct to me. I just have a minor naming suggestion:
since this helper returns a byte offset, while exFAT already has
exfat_cluster_to_sector() for sector-based addresses, would it be clearer to
name this helper exfat_cluster_to_phys_bytes()?

Thanks
DaeMyung

2026년 5월 13일 (수) 오후 8:27, Namjae Jeon <linkinjeon@xxxxxxxxxx>님이 작성:
>
> This caches the data area start offset in bytes (data_start_bytes)
> and introduces a helper function exfat_cluster_to_phys() to compute
> the physical byte position of a given cluster.
>
> Signed-off-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
> ---
>  fs/exfat/exfat_fs.h | 8 ++++++++
>  fs/exfat/super.c    | 1 +
>  2 files changed, 9 insertions(+)
>
> diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
> index 6e7fd6822b01..415f987afa9a 100644
> --- a/fs/exfat/exfat_fs.h
> +++ b/fs/exfat/exfat_fs.h
> @@ -227,6 +227,7 @@ struct exfat_sb_info {
>         unsigned long long FAT1_start_sector; /* FAT1 start sector */
>         unsigned long long FAT2_start_sector; /* FAT2 start sector */
>         unsigned long long data_start_sector; /* data area start sector */
> +       unsigned long long data_start_bytes;
>         unsigned int num_FAT_sectors; /* num of FAT sectors */
>         unsigned int root_dir; /* root dir cluster */
>         unsigned int dentries_per_clu; /* num of dentries per cluster */
> @@ -400,6 +401,13 @@ static inline loff_t exfat_ondisk_size(const struct inode *inode)
>         return ((loff_t)inode->i_blocks) << 9;
>  }
>
> +static inline loff_t exfat_cluster_to_phys(struct exfat_sb_info *sbi,
> +               unsigned int clus)
> +{
> +       return ((loff_t)(clus - EXFAT_RESERVED_CLUSTERS) << sbi->cluster_size_bits) +
> +               sbi->data_start_bytes;
> +}
> +
>  /*
>   * helpers for cluster size to byte conversion.
>   */
> diff --git a/fs/exfat/super.c b/fs/exfat/super.c
> index cb2f8eefff99..388db271c6bf 100644
> --- a/fs/exfat/super.c
> +++ b/fs/exfat/super.c
> @@ -499,6 +499,7 @@ static int exfat_read_boot_sector(struct super_block *sb)
>         if (p_boot->num_fats == 2)
>                 sbi->FAT2_start_sector += sbi->num_FAT_sectors;
>         sbi->data_start_sector = le32_to_cpu(p_boot->clu_offset);
> +       sbi->data_start_bytes = sbi->data_start_sector << p_boot->sect_size_bits;
>         sbi->num_sectors = le64_to_cpu(p_boot->vol_length);
>         /* because the cluster index starts with 2 */
>         sbi->num_clusters = le32_to_cpu(p_boot->clu_count) +
> --
> 2.25.1
>
>