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

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Message-ID: <6f43ef92-a9a4-4c9b-b0e0-0bfa579ad3e4@163.com>
Date: Sat, 29 Nov 2025 09:56:49 +0800
From: Chi Zhiling <chizhiling@....com>
To: "Yuezhang.Mo@...y.com" <Yuezhang.Mo@...y.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

On 11/28/25 19:09, Yuezhang.Mo@...y.com wrote:
>> 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.

Agreed, I will implement it in the next version.


Thanks,

> 
>> --
>> 2.43.0