[PATCH 2/2] iomap: introduce iomap_read/write_region interface

[Andrey Albershteyn <aalbersh@redhat.com>]

From: Andrey Albershteyn <aalbersh@redhat.com>

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

Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
---
 fs/iomap/buffered-io.c | 103 ++++++++++++++++++++++++++++++++++++++++-
 include/linux/iomap.h  |  13 ++++++
 2 files changed, 115 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 61ec924c5b80..0f33ac975209 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -325,6 +325,7 @@ struct iomap_readpage_ctx {
 	bool			cur_folio_in_bio;
 	struct bio		*bio;
 	struct readahead_control *rac;
+	int			flags;
 };
 
 /**
@@ -363,7 +364,8 @@ static inline bool iomap_block_needs_zeroing(const struct iomap_iter *iter,
 
 	return srcmap->type != IOMAP_MAPPED ||
 		(srcmap->flags & IOMAP_F_NEW) ||
-		pos >= i_size_read(iter->inode);
+		(pos >= i_size_read(iter->inode) &&
+		 !(srcmap->flags & IOMAP_F_BEYOND_EOF));
 }
 
 static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
@@ -2044,6 +2046,105 @@ iomap_writepages_unbound(struct address_space *mapping, struct writeback_control
 }
 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 | region->offset) >> PAGE_SHIFT;
+	struct folio *folio = __filemap_get_folio(inode->i_mapping, index, fgp,
+				    mapping_gfp_mask(inode->i_mapping));
+	struct iomap_readpage_ctx ctx = {
+		.cur_folio = folio,
+	};
+	struct iomap_iter iter = {
+		.inode = inode,
+		.pos = folio_pos(folio),
+		.len = folio_size(folio),
+	};
+	int ret;
+
+	if (folio_test_uptodate(folio)) {
+		folio_unlock(folio);
+		return folio;
+	}
+
+	while ((ret = iomap_iter(&iter, region->ops)) > 0)
+		iter.processed = iomap_readpage_iter(&iter, &ctx, 0);
+
+	if (ret < 0) {
+		folio_unlock(folio);
+		return ERR_PTR(ret);
+	}
+
+	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 loff_t iomap_write_region_iter(struct iomap_iter *iter, const void *buf)
+{
+	loff_t pos = iter->pos;
+	loff_t length = iomap_length(iter);
+	loff_t written = 0;
+
+	do {
+		struct folio *folio;
+		int status;
+		size_t offset;
+		size_t bytes = min_t(u64, SIZE_MAX, length);
+		bool ret;
+
+		status = iomap_write_begin(iter, pos, bytes, &folio);
+		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, pos, bytes, bytes, folio);
+		if (WARN_ON_ONCE(!ret))
+			return -EIO;
+
+		__iomap_put_folio(iter, pos, written, folio);
+
+		pos += bytes;
+		length -= bytes;
+		written += bytes;
+	} while (length > 0);
+
+	return written;
+}
+
+int
+iomap_write_region(struct ioregion *region)
+{
+	struct iomap_iter iter = {
+		.inode		= region->inode,
+		.pos		= region->pos | region->offset,
+		.len		= region->length,
+	};
+	ssize_t ret;
+
+	while ((ret = iomap_iter(&iter, region->ops)) > 0)
+		iter.processed = iomap_write_region_iter(&iter, region->buf);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iomap_write_region);
+
 static int __init iomap_buffered_init(void)
 {
 	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 3bfd3035ac28..3297ed36c26b 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -68,6 +68,7 @@ struct vm_fault;
 #endif /* CONFIG_BUFFER_HEAD */
 #define IOMAP_F_XATTR		(1U << 5)
 #define IOMAP_F_BOUNDARY	(1U << 6)
+#define IOMAP_F_BEYOND_EOF	(1U << 7)
 
 /*
  * Flags set by the core iomap code during operations:
@@ -458,4 +459,16 @@ int iomap_swapfile_activate(struct swap_info_struct *sis,
 # define iomap_swapfile_activate(sis, swapfile, pagespan, ops)	(-EIO)
 #endif /* CONFIG_SWAP */
 
+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 */
+	loff_t offset;				/* Region offset in the cache */
+	const struct iomap_ops *ops;
+};
+
+struct folio *iomap_read_region(struct ioregion *region);
+int iomap_write_region(struct ioregion *region);
+
 #endif /* LINUX_IOMAP_H */
-- 
2.47.0