[PATCH 11/12] iomap: add read_folio_range() handler for buffered writes

Christoph Hellwig
2025-06-27T07:04:04Z

From: Joanne Koong <joannelkoong@gmail.com>

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>
---
.../filesystems/iomap/operations.rst | 6 +++++
fs/iomap/buffered-io.c | 25 +++++++++++--------
include/linux/iomap.h | 10 ++++++++
3 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/Documentation/filesystems/iomap/operations.rst b/Documentation/filesystems/iomap/operations.rst
index 167d3ca7819c..04432f40e7a2 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``.
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index a77686977a2e..1a9ade77aeeb 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -667,22 +667,23 @@ iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
pos + len - 1);
}

-static int iomap_read_folio_sync(loff_t block_start, struct folio *folio,
- size_t poff, size_t plen, const struct iomap *iomap)
+static int iomap_read_folio_range(const struct iomap_iter *iter,
+ struct folio *folio, loff_t pos, size_t len)
{
+ const struct iomap *srcmap = iomap_iter_srcmap(iter);
struct bio_vec bvec;
struct bio bio;

- bio_init(&bio, iomap->bdev, &bvec, 1, REQ_OP_READ);
- bio.bi_iter.bi_sector = iomap_sector(iomap, block_start);
- bio_add_folio_nofail(&bio, folio, plen, poff);
+ bio_init(&bio, srcmap->bdev, &bvec, 1, REQ_OP_READ);
+ bio.bi_iter.bi_sector = iomap_sector(srcmap, pos);
+ bio_add_folio_nofail(&bio, folio, len, offset_in_folio(folio, pos));
return submit_bio_wait(&bio);
}

-static int __iomap_write_begin(const struct iomap_iter *iter, size_t len,
+static int __iomap_write_begin(const struct iomap_iter *iter,
+ const struct iomap_write_ops *write_ops, size_t len,
struct folio *folio)
{
- const struct iomap *srcmap = iomap_iter_srcmap(iter);
struct iomap_folio_state *ifs;
loff_t pos = iter->pos;
loff_t block_size = i_blocksize(iter->inode);
@@ -731,8 +732,12 @@ static int __iomap_write_begin(const struct iomap_iter *iter, size_t len,
if (iter->flags & IOMAP_NOWAIT)
return -EAGAIN;

- status = iomap_read_folio_sync(block_start, folio,
- poff, plen, srcmap);
+ if (write_ops && write_ops->read_folio_range)
+ status = write_ops->read_folio_range(iter,
+ folio, block_start, plen);
+ else
+ status = iomap_read_folio_range(iter,
+ folio, block_start, plen);
if (status)
return status;
}
@@ -848,7 +853,7 @@ static int iomap_write_begin(struct iomap_iter *iter,
else if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
status = __block_write_begin_int(folio, pos, len, NULL, srcmap);
else
- status = __iomap_write_begin(iter, len, folio);
+ status = __iomap_write_begin(iter, write_ops, len, folio);

if (unlikely(status))
goto out_unlock;
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 482787013ff7..b3588dd43105 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -166,6 +166,16 @@ struct iomap_write_ops {
* locked by the iomap code.
*/
bool (*iomap_valid)(struct inode *inode, const struct iomap *iomap);
+
+ /*
+ * Optional if the filesystem wishes to provide a custom handler for
+ * reading in the contents of a folio, otherwise iomap will default to
+ * submitting a bio read request.
+ *
+ * The read must be done synchronously.
+ */
+ int (*read_folio_range)(const struct iomap_iter *iter,
+ struct folio *folio, loff_t pos, size_t len);
};

/*
--
2.47.2