[PATCH RFC 02/29] iomap: introduce iomap_read/write_region interface

[Andrey Albershteyn <aalbersh@redhat.com>]

From: Andrey Albershteyn <aalbersh@redhat.com>

Interface for writing data beyond EOF into offsetted region in
page cache.

Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
---
 fs/iomap/buffered-io.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++-
 include/linux/iomap.h  | 16 ++++++++
 2 files changed, 114 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 7bef232254a3..e959a206cba9 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -321,6 +321,7 @@ struct iomap_readpage_ctx {
 	bool			cur_folio_in_bio;
 	struct bio		*bio;
 	struct readahead_control *rac;
+	int			flags;
 };
 
 /**
@@ -387,7 +388,8 @@ static int iomap_readpage_iter(struct iomap_iter *iter,
 	if (plen == 0)
 		goto done;
 
-	if (iomap_block_needs_zeroing(iter, pos)) {
+	if (iomap_block_needs_zeroing(iter, pos) &&
+	    !(iomap->flags & IOMAP_F_BEYOND_EOF)) {
 		folio_zero_range(folio, poff, plen);
 		iomap_set_range_uptodate(folio, poff, plen);
 		goto done;
@@ -2007,3 +2009,98 @@ iomap_writepages_unbound(struct address_space *mapping, struct writeback_control
 	return iomap_submit_ioend(wpc, error);
 }
 EXPORT_SYMBOL_GPL(iomap_writepages_unbound);
+
+struct folio *
+iomap_read_region(struct ioregion *region)
+{
+	struct inode *inode = region->inode;
+	fgf_t fgp = FGP_CREAT | FGP_LOCK | fgf_set_order(region->length);
+	pgoff_t index = (region->pos) >> PAGE_SHIFT;
+	struct folio *folio = __filemap_get_folio(inode->i_mapping, index, fgp,
+				    mapping_gfp_mask(inode->i_mapping));
+	int ret;
+	struct iomap_iter iter = {
+		.inode		= folio->mapping->host,
+		.pos		= region->pos,
+		.len		= region->length,
+	};
+	struct iomap_readpage_ctx ctx = {
+		.cur_folio	= folio,
+	};
+
+	if (folio_test_uptodate(folio)) {
+		folio_unlock(folio);
+		return folio;
+	}
+
+	while ((ret = iomap_iter(&iter, region->ops)) > 0)
+		iter.status = iomap_read_folio_iter(&iter, &ctx);
+
+	if (ctx.bio) {
+		submit_bio(ctx.bio);
+		WARN_ON_ONCE(!ctx.cur_folio_in_bio);
+	} else {
+		WARN_ON_ONCE(ctx.cur_folio_in_bio);
+		folio_unlock(folio);
+	}
+
+	return folio;
+}
+EXPORT_SYMBOL_GPL(iomap_read_region);
+
+static int iomap_write_region_iter(struct iomap_iter *iter, const void *buf)
+{
+	loff_t pos = iter->pos;
+	u64 bytes = iomap_length(iter);
+	int status;
+
+	do {
+		struct folio *folio;
+		size_t offset;
+		bool ret;
+
+		bytes = min_t(u64, SIZE_MAX, bytes);
+		status = iomap_write_begin(iter, &folio, &offset, &bytes);
+		if (status)
+			return status;
+		if (iter->iomap.flags & IOMAP_F_STALE)
+			break;
+
+		offset = offset_in_folio(folio, pos);
+		if (bytes > folio_size(folio) - offset)
+			bytes = folio_size(folio) - offset;
+
+		memcpy_to_folio(folio, offset, buf, bytes);
+
+		ret = iomap_write_end(iter, bytes, bytes, folio);
+		if (WARN_ON_ONCE(!ret))
+			return -EIO;
+
+		__iomap_put_folio(iter, bytes, folio);
+		if (WARN_ON_ONCE(!ret))
+			return -EIO;
+
+		status = iomap_iter_advance(iter, &bytes);
+		if (status)
+			break;
+	} while (bytes > 0);
+
+	return status;
+}
+
+int
+iomap_write_region(struct ioregion *region)
+{
+	struct iomap_iter iter = {
+		.inode		= region->inode,
+		.pos		= region->pos,
+		.len		= region->length,
+	};
+	ssize_t ret;
+
+	while ((ret = iomap_iter(&iter, region->ops)) > 0)
+		iter.status = iomap_write_region_iter(&iter, region->buf);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(iomap_write_region);
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 4a0b5ebb79e9..73288f28543f 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -83,6 +83,11 @@ struct vm_fault;
  */
 #define IOMAP_F_PRIVATE		(1U << 12)
 
+/*
+ * Writes happens beyound inode EOF
+ */
+#define IOMAP_F_BEYOND_EOF	(1U << 13)
+
 /*
  * Flags set by the core iomap code during operations:
  *
@@ -533,4 +538,15 @@ int iomap_swapfile_activate(struct swap_info_struct *sis,
 
 extern struct bio_set iomap_ioend_bioset;
 
+struct ioregion {
+	struct inode *inode;
+	loff_t pos;				/* IO position */
+	const void *buf;			/* Data to be written (in only) */
+	size_t length;				/* Length of the date */
+	const struct iomap_ops *ops;
+};
+
+struct folio *iomap_read_region(struct ioregion *region);
+int iomap_write_region(struct ioregion *region);
+
 #endif /* LINUX_IOMAP_H */

-- 
2.50.0