linux-kernel - Re: [RFC PATCH 6/7] exfat: introduce exfat_count_contig

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Message-ID:
 <PUZPR04MB6316A47C9E593BCF7EB550B881DCA@PUZPR04MB6316.apcprd04.prod.outlook.com>
Date: Fri, 28 Nov 2025 11:09:01 +0000
From: "Yuezhang.Mo@...y.com" <Yuezhang.Mo@...y.com>
To: Chi Zhiling <chizhiling@....com>,
        "linux-fsdevel@...r.kernel.org"
	<linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner
	<brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox
	<willy@...radead.org>,
        Namjae Jeon <linkinjeon@...nel.org>,
        Sungjong Seo
	<sj1557.seo@...sung.com>,
        Chi Zhiling <chizhiling@...inos.cn>
Subject: Re: [RFC PATCH 6/7] exfat: introduce exfat_count_contig_clusters

> From: Chi Zhiling <chizhiling@...inos.cn>
> 
> This patch introduces exfat_count_contig_clusters to obtain batch entries,
> which is an infrastructure used to support iomap.
> 
> Signed-off-by: Chi Zhiling <chizhiling@...inos.cn>
> ---
>  fs/exfat/exfat_fs.h |  2 ++
>  fs/exfat/fatent.c   | 33 +++++++++++++++++++++++++++++++++
>  2 files changed, 35 insertions(+)
> 
> diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
> index d52893276e9a..421dd7c61cca 100644
> --- a/fs/exfat/exfat_fs.h
> +++ b/fs/exfat/exfat_fs.h
> @@ -449,6 +449,8 @@ int exfat_find_last_cluster(struct super_block *sb, struct exfat_chain *p_chain,
>                 unsigned int *ret_clu);
>  int exfat_count_num_clusters(struct super_block *sb,
>                 struct exfat_chain *p_chain, unsigned int *ret_count);
> +int exfat_count_contig_clusters(struct super_block *sb,
> +               struct exfat_chain *p_chain, unsigned int *ret_count);
> 
>  /* balloc.c */
>  int exfat_load_bitmap(struct super_block *sb);
> diff --git a/fs/exfat/fatent.c b/fs/exfat/fatent.c
> index d980d17176c2..9dcee9524155 100644
> --- a/fs/exfat/fatent.c
> +++ b/fs/exfat/fatent.c
> @@ -524,3 +524,36 @@ int exfat_count_num_clusters(struct super_block *sb,
> 
>         return 0;
>  }
> +
> +int exfat_count_contig_clusters(struct super_block *sb,
> +               struct exfat_chain *p_chain, unsigned int *ret_count)
> +{
> +       struct buffer_head *bh = NULL;
> +       unsigned int clu, next_clu;
> +       unsigned int count;
> +
> +       if (!p_chain->dir || p_chain->dir == EXFAT_EOF_CLUSTER) {
> +               *ret_count = 0;
> +               return 0;
> +       }
> +
> +       if (p_chain->flags == ALLOC_NO_FAT_CHAIN) {
> +               *ret_count = p_chain->size;
> +               return 0;
> +       }
> +
> +       clu = p_chain->dir;
> +       for (count = 1; count < p_chain->size; count++) {
> +               if (exfat_ent_get(sb, clu, &next_clu, &bh))
> +                       return -EIO;
> +               if (++clu != next_clu)
> +                       break;
> +       }
> +
> +       /* TODO: Update p_claim to help caller read ahead the next block */
> +
> +       brelse(bh);
> +       *ret_count = count;
> +
> +       return 0;
> +}

Hi Chi,

The clusters traversed in exfat_get_cluster() are cached to
->cache_lru, but the clusters traversed in this function are
not.

I think we can implement this functionality in exfat_get_cluster()
and cache the clusters.

> --
> 2.43.0