Re: [PATCH v8 1/9] iomap: stash iomap read ctx in the private field of iomap_iter

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On 2025/11/14 17:55, 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@huawei.com>
> ---
>   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 8275b6681b9b..98dd20f0bb53 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -973,7 +973,7 @@ 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;
>   }
> @@ -1075,7 +1075,7 @@ 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 6ae031ac8058..8e79303c074e 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -496,13 +496,14 @@ 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_pending = 0;
>   	int ret;
> @@ -560,13 +561,14 @@ 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_pending;
>   
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 8b1ac08c7474..c3ecbbdb14e8 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);
> @@ -594,7 +594,7 @@ 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,
> @@ -605,7 +605,7 @@ static inline void iomap_bio_readahead(struct readahead_control *rac,
>   		.rac		= rac,
>   	};
>   
> -	iomap_readahead(ops, &ctx);
> +	iomap_readahead(ops, &ctx, NULL);
>   }
>   #endif /* CONFIG_BLOCK */
>