linux-kernel - Re: [PATCH v13 01/10] iomap: stash iomap read ctx in the private field of iomap

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Message-ID: <659a02c2-cd90-40d4-82b6-f6010e8bcf98@huawei.com>
Date: Fri, 9 Jan 2026 18:43:31 +0800
From: Hongbo Li <lihongbo22@...wei.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>, Christoph Hellwig <hch@....de>,
	"Darrick J. Wong" <djwong@...nel.org>, Christian Brauner <brauner@...nel.org>
CC: <amir73il@...il.com>, <linux-fsdevel@...r.kernel.org>,
	<linux-erofs@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>, Chao Yu
	<chao@...nel.org>
Subject: Re: [PATCH v13 01/10] iomap: stash iomap read ctx in the private
 field of iomap_iter

Hi, all

On 2026/1/9 14:03, Gao Xiang wrote:
> Hi Christoph, Darrick, Christian,
> 
> On 2026/1/9 11:01, Hongbo Li wrote:
>> It's useful to get filesystem-specific information using the
>> existing private field in the @iomap_iter passed to iomap_{begin,end}
>> for advanced usage for iomap buffered reads, which is much like the
>> current iomap DIO.
>>
>> For example, EROFS needs it to:
>>
>>   - implement an efficient page cache sharing feature, since iomap
>>     needs to apply to anon inode page cache but we'd like to get the
>>     backing inode/fs instead, so filesystem-specific private data is
>>     needed to keep such information;
>>
>>   - pass in both struct page * and void * for inline data to avoid
>>     kmap_to_page() usage (which is bogus).
>>
>> Signed-off-by: Hongbo Li <lihongbo22@...wei.com>
>> Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
> 
> Could you help review or ack this patch?
> 
> This feature is almost in shape for the upcoming cycle,
> I do hope this iomap patch could be reviewed, thanks!
> 

I have sent the latest version v14. Could you help review or ack based 
on the latest one?

Thanks,
Hongbo

> Thanks,
> Gao Xiang
> 
>> ---
>>   fs/fuse/file.c         | 4 ++--
>>   fs/iomap/buffered-io.c | 6 ++++--
>>   include/linux/iomap.h  | 8 ++++----
>>   3 files changed, 10 insertions(+), 8 deletions(-)
>>
>> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
>> index 01bc894e9c2b..f5d8887c1922 100644
>> --- a/fs/fuse/file.c
>> +++ b/fs/fuse/file.c
>> @@ -979,7 +979,7 @@ static int fuse_read_folio(struct file *file, 
>> struct folio *folio)
>>           return -EIO;
>>       }
>> -    iomap_read_folio(&fuse_iomap_ops, &ctx);
>> +    iomap_read_folio(&fuse_iomap_ops, &ctx, NULL);
>>       fuse_invalidate_atime(inode);
>>       return 0;
>>   }
>> @@ -1081,7 +1081,7 @@ static void fuse_readahead(struct 
>> readahead_control *rac)
>>       if (fuse_is_bad(inode))
>>           return;
>> -    iomap_readahead(&fuse_iomap_ops, &ctx);
>> +    iomap_readahead(&fuse_iomap_ops, &ctx, NULL);
>>   }
>>   static ssize_t fuse_cache_read_iter(struct kiocb *iocb, struct 
>> iov_iter *to)
>> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
>> index e5c1ca440d93..5f7dcbabbda3 100644
>> --- a/fs/iomap/buffered-io.c
>> +++ b/fs/iomap/buffered-io.c
>> @@ -555,13 +555,14 @@ static int iomap_read_folio_iter(struct 
>> iomap_iter *iter,
>>   }
>>   void iomap_read_folio(const struct iomap_ops *ops,
>> -        struct iomap_read_folio_ctx *ctx)
>> +        struct iomap_read_folio_ctx *ctx, void *private)
>>   {
>>       struct folio *folio = ctx->cur_folio;
>>       struct iomap_iter iter = {
>>           .inode        = folio->mapping->host,
>>           .pos        = folio_pos(folio),
>>           .len        = folio_size(folio),
>> +        .private    = private,
>>       };
>>       size_t bytes_submitted = 0;
>>       int ret;
>> @@ -620,13 +621,14 @@ static int iomap_readahead_iter(struct 
>> iomap_iter *iter,
>>    * the filesystem to be reentered.
>>    */
>>   void iomap_readahead(const struct iomap_ops *ops,
>> -        struct iomap_read_folio_ctx *ctx)
>> +        struct iomap_read_folio_ctx *ctx, void *private)
>>   {
>>       struct readahead_control *rac = ctx->rac;
>>       struct iomap_iter iter = {
>>           .inode    = rac->mapping->host,
>>           .pos    = readahead_pos(rac),
>>           .len    = readahead_length(rac),
>> +        .private = private,
>>       };
>>       size_t cur_bytes_submitted;
>> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
>> index 520e967cb501..441d614e9fdf 100644
>> --- a/include/linux/iomap.h
>> +++ b/include/linux/iomap.h
>> @@ -341,9 +341,9 @@ ssize_t iomap_file_buffered_write(struct kiocb 
>> *iocb, struct iov_iter *from,
>>           const struct iomap_ops *ops,
>>           const struct iomap_write_ops *write_ops, void *private);
>>   void iomap_read_folio(const struct iomap_ops *ops,
>> -        struct iomap_read_folio_ctx *ctx);
>> +        struct iomap_read_folio_ctx *ctx, void *private);
>>   void iomap_readahead(const struct iomap_ops *ops,
>> -        struct iomap_read_folio_ctx *ctx);
>> +        struct iomap_read_folio_ctx *ctx, void *private);
>>   bool iomap_is_partially_uptodate(struct folio *, size_t from, size_t 
>> count);
>>   struct folio *iomap_get_folio(struct iomap_iter *iter, loff_t pos, 
>> size_t len);
>>   bool iomap_release_folio(struct folio *folio, gfp_t gfp_flags);
>> @@ -595,7 +595,7 @@ static inline void iomap_bio_read_folio(struct 
>> folio *folio,
>>           .cur_folio    = folio,
>>       };
>> -    iomap_read_folio(ops, &ctx);
>> +    iomap_read_folio(ops, &ctx, NULL);
>>   }
>>   static inline void iomap_bio_readahead(struct readahead_control *rac,
>> @@ -606,7 +606,7 @@ static inline void iomap_bio_readahead(struct 
>> readahead_control *rac,
>>           .rac        = rac,
>>       };
>> -    iomap_readahead(ops, &ctx);
>> +    iomap_readahead(ops, &ctx, NULL);
>>   }
>>   #endif /* CONFIG_BLOCK */
>