From: Chi Zhiling <chizhiling@kylinos.cn>

mpage uses the get_block of the file system to obtain the mapping of a
file or allocate blocks for writes. Currently exfat only supports
obtaining one cluster in each get_block call.

Since exfat_count_contig_clusters can obtain multiple consecutive clusters,
it can be used to improve exfat_get_block when page size is larger than
cluster size.

Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
---
 fs/exfat/inode.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
index f9501c3a3666..256ba2af34eb 100644
--- a/fs/exfat/inode.c
+++ b/fs/exfat/inode.c
@@ -264,13 +264,14 @@ static int exfat_map_cluster(struct inode *inode, unsigned int clu_offset,
 static int exfat_get_block(struct inode *inode, sector_t iblock,
 		struct buffer_head *bh_result, int create)
 {
+	struct exfat_chain chain;
 	struct exfat_inode_info *ei = EXFAT_I(inode);
 	struct super_block *sb = inode->i_sb;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
 	unsigned long max_blocks = bh_result->b_size >> inode->i_blkbits;
 	int err = 0;
 	unsigned long mapped_blocks = 0;
-	unsigned int cluster, sec_offset;
+	unsigned int cluster, sec_offset, count;
 	sector_t last_block;
 	sector_t phys = 0;
 	sector_t valid_blks;
@@ -301,6 +302,17 @@ static int exfat_get_block(struct inode *inode, sector_t iblock,
 
 	phys = exfat_cluster_to_sector(sbi, cluster) + sec_offset;
 	mapped_blocks = sbi->sect_per_clus - sec_offset;
+
+	if (max_blocks > mapped_blocks && !create) {
+		chain.dir = cluster;
+		chain.size = (max_blocks >> sbi->sect_per_clus_bits) + 1;
+		chain.flags = ei->flags;
+
+		err = exfat_count_contig_clusters(sb, &chain, &count);
+		if (err)
+			return err;
+		max_blocks = (count << sbi->sect_per_clus_bits) - sec_offset;
+	}
 	max_blocks = min(mapped_blocks, max_blocks);
 
 	map_bh(bh_result, sb, phys);
-- 
2.43.0

Hi, Chi,
On 25. 11. 18. 17:22, Chi Zhiling wrote:
> From: Chi Zhiling <chizhiling@kylinos.cn>
> 
> mpage uses the get_block of the file system to obtain the mapping of a
> file or allocate blocks for writes. Currently exfat only supports
> obtaining one cluster in each get_block call.
> 
> Since exfat_count_contig_clusters can obtain multiple consecutive clusters,
> it can be used to improve exfat_get_block when page size is larger than
> cluster size.

I think reusing buffer_head is a good approach!
However, for obtaining multiple clusters, it would be better to handle
them in exfat_map_cluster.

> 
> Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
> ---
>  fs/exfat/inode.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
> index f9501c3a3666..256ba2af34eb 100644
> --- a/fs/exfat/inode.c
> +++ b/fs/exfat/inode.c
> @@ -264,13 +264,14 @@ static int exfat_map_cluster(struct inode *inode, unsigned int clu_offset,
>  static int exfat_get_block(struct inode *inode, sector_t iblock,
>  		struct buffer_head *bh_result, int create)
>  {
> +	struct exfat_chain chain;
>  	struct exfat_inode_info *ei = EXFAT_I(inode);
>  	struct super_block *sb = inode->i_sb;
>  	struct exfat_sb_info *sbi = EXFAT_SB(sb);
>  	unsigned long max_blocks = bh_result->b_size >> inode->i_blkbits;
>  	int err = 0;
>  	unsigned long mapped_blocks = 0;
> -	unsigned int cluster, sec_offset;
> +	unsigned int cluster, sec_offset, count;
>  	sector_t last_block;
>  	sector_t phys = 0;
>  	sector_t valid_blks;
> @@ -301,6 +302,17 @@ static int exfat_get_block(struct inode *inode, sector_t iblock,
>  
>  	phys = exfat_cluster_to_sector(sbi, cluster) + sec_offset;
>  	mapped_blocks = sbi->sect_per_clus - sec_offset;
> +
> +	if (max_blocks > mapped_blocks && !create) {
> +		chain.dir = cluster;
> +		chain.size = (max_blocks >> sbi->sect_per_clus_bits) + 1;

There seems to be an issue where the code sets chain.size to be one greater than the actual cluster count.

For example, assuming a 16KiB page, 512B sector, and 4KiB cluster,
for a 16KiB file, chain.size becomes 5 instead of 4.
Is this the intended behavior?

> +		chain.flags = ei->flags;
> +
> +		err = exfat_count_contig_clusters(sb, &chain, &count);
> +		if (err)
> +			return err;
> +		max_blocks = (count << sbi->sect_per_clus_bits) - sec_offset;

You already said mapped_blocks is correct.

> +	}
>  	max_blocks = min(mapped_blocks, max_blocks);
>  
>  	map_bh(bh_result, sb, phys);

On 11/28/25 10:48, Sungjong Seo wrote:
> 
> Hi, Chi,
> On 25. 11. 18. 17:22, Chi Zhiling wrote:
>> From: Chi Zhiling <chizhiling@kylinos.cn>
>>
>> mpage uses the get_block of the file system to obtain the mapping of a
>> file or allocate blocks for writes. Currently exfat only supports
>> obtaining one cluster in each get_block call.
>>
>> Since exfat_count_contig_clusters can obtain multiple consecutive clusters,
>> it can be used to improve exfat_get_block when page size is larger than
>> cluster size.
> 
> I think reusing buffer_head is a good approach!
> However, for obtaining multiple clusters, it would be better to handle
> them in exfat_map_cluster.

Hi, Sungjong

I agree.

My original plan was to support multiple clusters for exfat_map_cluster 
and exfat_get_cluster. since the changes required were quite extensive, 
I put that plan on hold. This would likely involve refactoring 
exfat_map_clusterand introducing iterators to reduce the number of 
parameters it needs

I will take some time to consider the signature of the new 
exfat_map_clusters. Do you have any thoughts about this?

> 
>>
>> Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
>> ---
>>   fs/exfat/inode.c | 14 +++++++++++++-
>>   1 file changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
>> index f9501c3a3666..256ba2af34eb 100644
>> --- a/fs/exfat/inode.c
>> +++ b/fs/exfat/inode.c
>> @@ -264,13 +264,14 @@ static int exfat_map_cluster(struct inode *inode, unsigned int clu_offset,
>>   static int exfat_get_block(struct inode *inode, sector_t iblock,
>>   		struct buffer_head *bh_result, int create)
>>   {
>> +	struct exfat_chain chain;
>>   	struct exfat_inode_info *ei = EXFAT_I(inode);
>>   	struct super_block *sb = inode->i_sb;
>>   	struct exfat_sb_info *sbi = EXFAT_SB(sb);
>>   	unsigned long max_blocks = bh_result->b_size >> inode->i_blkbits;
>>   	int err = 0;
>>   	unsigned long mapped_blocks = 0;
>> -	unsigned int cluster, sec_offset;
>> +	unsigned int cluster, sec_offset, count;
>>   	sector_t last_block;
>>   	sector_t phys = 0;
>>   	sector_t valid_blks;
>> @@ -301,6 +302,17 @@ static int exfat_get_block(struct inode *inode, sector_t iblock,
>>   
>>   	phys = exfat_cluster_to_sector(sbi, cluster) + sec_offset;
>>   	mapped_blocks = sbi->sect_per_clus - sec_offset;
>> +
>> +	if (max_blocks > mapped_blocks && !create) {
>> +		chain.dir = cluster;
>> +		chain.size = (max_blocks >> sbi->sect_per_clus_bits) + 1;
> 
> There seems to be an issue where the code sets chain.size to be one greater than the actual cluster count.
> 
> For example, assuming a 16KiB page, 512B sector, and 4KiB cluster,
> for a 16KiB file, chain.size becomes 5 instead of 4.
> Is this the intended behavior?

This is not the expected behavior. It's a serious bug. Thank you very 
much for pointing this out.

> 
>> +		chain.flags = ei->flags;
>> +
>> +		err = exfat_count_contig_clusters(sb, &chain, &count);
>> +		if (err)
>> +			return err;
>> +		max_blocks = (count << sbi->sect_per_clus_bits) - sec_offset;
> 
> You already said mapped_blocks is correct.
> 
>> +	}
>>   	max_blocks = min(mapped_blocks, max_blocks);
>>   
>>   	map_bh(bh_result, sb, phys);

On 25. 11. 28. 15:18, Chi Zhiling wrote:
> On 11/28/25 10:48, Sungjong Seo wrote:
>>
>> Hi, Chi,
>> On 25. 11. 18. 17:22, Chi Zhiling wrote:
>>> From: Chi Zhiling <chizhiling@kylinos.cn>
>>>
>>> mpage uses the get_block of the file system to obtain the mapping of a
>>> file or allocate blocks for writes. Currently exfat only supports
>>> obtaining one cluster in each get_block call.
>>>
>>> Since exfat_count_contig_clusters can obtain multiple consecutive clusters,
>>> it can be used to improve exfat_get_block when page size is larger than
>>> cluster size.
>>
>> I think reusing buffer_head is a good approach!
>> However, for obtaining multiple clusters, it would be better to handle
>> them in exfat_map_cluster.
> 
> Hi, Sungjong
> 
> I agree.
> 
> My original plan was to support multiple clusters for exfat_map_cluster and exfat_get_cluster. since the changes required were quite extensive, I put that plan on hold. This would likely involve refactoring exfat_map_clusterand introducing iterators to reduce the number of parameters it needs
> 
> I will take some time to consider the signature of the new exfat_map_clusters. Do you have any thoughts about this?
Apologies, I missed your email.
IMO, we don't need to rush, so I think expanding exfat_map_cluster(s) would be better.

Thanks.
> 
>>
>>>
>>> Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
>>> ---
>>>   fs/exfat/inode.c | 14 +++++++++++++-
>>>   1 file changed, 13 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
>>> index f9501c3a3666..256ba2af34eb 100644
>>> --- a/fs/exfat/inode.c
>>> +++ b/fs/exfat/inode.c
>>> @@ -264,13 +264,14 @@ static int exfat_map_cluster(struct inode *inode, unsigned int clu_offset,
>>>   static int exfat_get_block(struct inode *inode, sector_t iblock,
>>>           struct buffer_head *bh_result, int create)
>>>   {
>>> +    struct exfat_chain chain;
>>>       struct exfat_inode_info *ei = EXFAT_I(inode);
>>>       struct super_block *sb = inode->i_sb;
>>>       struct exfat_sb_info *sbi = EXFAT_SB(sb);
>>>       unsigned long max_blocks = bh_result->b_size >> inode->i_blkbits;
>>>       int err = 0;
>>>       unsigned long mapped_blocks = 0;
>>> -    unsigned int cluster, sec_offset;
>>> +    unsigned int cluster, sec_offset, count;
>>>       sector_t last_block;
>>>       sector_t phys = 0;
>>>       sector_t valid_blks;
>>> @@ -301,6 +302,17 @@ static int exfat_get_block(struct inode *inode, sector_t iblock,
>>>         phys = exfat_cluster_to_sector(sbi, cluster) + sec_offset;
>>>       mapped_blocks = sbi->sect_per_clus - sec_offset;
>>> +
>>> +    if (max_blocks > mapped_blocks && !create) {
>>> +        chain.dir = cluster;
>>> +        chain.size = (max_blocks >> sbi->sect_per_clus_bits) + 1;
>>
>> There seems to be an issue where the code sets chain.size to be one greater than the actual cluster count.
>>
>> For example, assuming a 16KiB page, 512B sector, and 4KiB cluster,
>> for a 16KiB file, chain.size becomes 5 instead of 4.
>> Is this the intended behavior?
> 
> This is not the expected behavior. It's a serious bug. Thank you very much for pointing this out.
> 
>>
>>> +        chain.flags = ei->flags;
>>> +
>>> +        err = exfat_count_contig_clusters(sb, &chain, &count);
>>> +        if (err)
>>> +            return err;
>>> +        max_blocks = (count << sbi->sect_per_clus_bits) - sec_offset;
>>
>> You already said mapped_blocks is correct.
>>
>>> +    }
>>>       max_blocks = min(mapped_blocks, max_blocks);
>>>         map_bh(bh_result, sb, phys);
> 
> 

On 12/4/25 20:18, Sungjong Seo wrote:
> 
> 
> On 25. 11. 28. 15:18, Chi Zhiling wrote:
>> On 11/28/25 10:48, Sungjong Seo wrote:
>>>
>>> Hi, Chi,
>>> On 25. 11. 18. 17:22, Chi Zhiling wrote:
>>>> From: Chi Zhiling <chizhiling@kylinos.cn>
>>>>
>>>> mpage uses the get_block of the file system to obtain the mapping of a
>>>> file or allocate blocks for writes. Currently exfat only supports
>>>> obtaining one cluster in each get_block call.
>>>>
>>>> Since exfat_count_contig_clusters can obtain multiple consecutive clusters,
>>>> it can be used to improve exfat_get_block when page size is larger than
>>>> cluster size.
>>>
>>> I think reusing buffer_head is a good approach!
>>> However, for obtaining multiple clusters, it would be better to handle
>>> them in exfat_map_cluster.
>>
>> Hi, Sungjong
>>
>> I agree.
>>
>> My original plan was to support multiple clusters for exfat_map_cluster and exfat_get_cluster. since the changes required were quite extensive, I put that plan on hold. This would likely involve refactoring exfat_map_clusterand introducing iterators to reduce the number of parameters it needs
>>
>> I will take some time to consider the signature of the new exfat_map_clusters. Do you have any thoughts about this?
> Apologies, I missed your email.
> IMO, we don't need to rush, so I think expanding exfat_map_cluster(s) would be better.

Okay.

> 
> Thanks.
>>
>>>
>>>>
>>>> Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
>>>> ---
>>>>    fs/exfat/inode.c | 14 +++++++++++++-
>>>>    1 file changed, 13 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
>>>> index f9501c3a3666..256ba2af34eb 100644
>>>> --- a/fs/exfat/inode.c
>>>> +++ b/fs/exfat/inode.c
>>>> @@ -264,13 +264,14 @@ static int exfat_map_cluster(struct inode *inode, unsigned int clu_offset,
>>>>    static int exfat_get_block(struct inode *inode, sector_t iblock,
>>>>            struct buffer_head *bh_result, int create)
>>>>    {
>>>> +    struct exfat_chain chain;
>>>>        struct exfat_inode_info *ei = EXFAT_I(inode);
>>>>        struct super_block *sb = inode->i_sb;
>>>>        struct exfat_sb_info *sbi = EXFAT_SB(sb);
>>>>        unsigned long max_blocks = bh_result->b_size >> inode->i_blkbits;
>>>>        int err = 0;
>>>>        unsigned long mapped_blocks = 0;
>>>> -    unsigned int cluster, sec_offset;
>>>> +    unsigned int cluster, sec_offset, count;
>>>>        sector_t last_block;
>>>>        sector_t phys = 0;
>>>>        sector_t valid_blks;
>>>> @@ -301,6 +302,17 @@ static int exfat_get_block(struct inode *inode, sector_t iblock,
>>>>          phys = exfat_cluster_to_sector(sbi, cluster) + sec_offset;
>>>>        mapped_blocks = sbi->sect_per_clus - sec_offset;
>>>> +
>>>> +    if (max_blocks > mapped_blocks && !create) {
>>>> +        chain.dir = cluster;
>>>> +        chain.size = (max_blocks >> sbi->sect_per_clus_bits) + 1;
>>>
>>> There seems to be an issue where the code sets chain.size to be one greater than the actual cluster count.
>>>
>>> For example, assuming a 16KiB page, 512B sector, and 4KiB cluster,
>>> for a 16KiB file, chain.size becomes 5 instead of 4.
>>> Is this the intended behavior?
>>
>> This is not the expected behavior. It's a serious bug. Thank you very much for pointing this out.
>>
>>>
>>>> +        chain.flags = ei->flags;
>>>> +
>>>> +        err = exfat_count_contig_clusters(sb, &chain, &count);
>>>> +        if (err)
>>>> +            return err;
>>>> +        max_blocks = (count << sbi->sect_per_clus_bits) - sec_offset;
>>>
>>> You already said mapped_blocks is correct.
>>>
>>>> +    }
>>>>        max_blocks = min(mapped_blocks, max_blocks);
>>>>          map_bh(bh_result, sb, phys);
>>
>>