iomap: add read_folio_range() handler for buffered writes

Add a read_folio_range() handler for buffered writes that filesystems
may pass in if they wish to provide a custom handler for synchronously
reading in the contents of a folio.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
[hch: renamed to read_folio_range, pass less arguments]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/20250710133343.399917-14-hch@lst.de
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/Documentation/filesystems/iomap/operations.rst b/Documentation/filesystems/iomap/operations.rst
index a9b48ce4af92..067ed8e14ef3 100644
--- a/Documentation/filesystems/iomap/operations.rst
+++ b/Documentation/filesystems/iomap/operations.rst
@@ -68,6 +68,8 @@ The following address space operations can be wrapped easily:
      void (*put_folio)(struct inode *inode, loff_t pos, unsigned copied,
                        struct folio *folio);
      bool (*iomap_valid)(struct inode *inode, const struct iomap *iomap);
+     int (*read_folio_range)(const struct iomap_iter *iter,
+     			struct folio *folio, loff_t pos, size_t len);
  };
 
 iomap calls these functions:
@@ -123,6 +125,10 @@ iomap calls these functions:
     ``->iomap_valid``, then the iomap should considered stale and the
     validation failed.
 
+  - ``read_folio_range``: Called to synchronously read in the range that will
+    be written to. If this function is not provided, iomap will default to
+    submitting a bio read request.
+
 These ``struct kiocb`` flags are significant for buffered I/O with iomap:
 
  * ``IOCB_NOWAIT``: Turns on ``IOMAP_NOWAIT``.