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

[Gao Xiang]

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 <lihongb...@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 */