From: Zhang Yi <yi.zhang@huawei.com>

Introduce a new iomap_ops, ext4_iomap_buffered_read_ops to implement the
iomap read paths, specifically .read_folio() and .readahead() of
ext4_iomap_aops. This .iomap_begin() handle invokes ext4_map_blocks() to
query the extent mapping status of the read range and then converts the
mapping information to iomap.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/ext4/inode.c | 37 +++++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index b233f36efefa..f0bc4b58ac4f 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3526,14 +3526,47 @@ const struct iomap_ops ext4_iomap_report_ops = {
 	.iomap_begin = ext4_iomap_begin_report,
 };
 
-static int ext4_iomap_read_folio(struct file *file, struct folio *folio)
+static int ext4_iomap_buffered_read_begin(struct inode *inode, loff_t offset,
+			loff_t length, unsigned int flags, struct iomap *iomap,
+			struct iomap *srcmap)
 {
+	int ret;
+	struct ext4_map_blocks map;
+	u8 blkbits = inode->i_blkbits;
+
+	if (unlikely(ext4_forced_shutdown(inode->i_sb)))
+		return -EIO;
+	if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
+		return -EINVAL;
+	/* Inline data support is not yet available. */
+	if (WARN_ON_ONCE(ext4_has_inline_data(inode)))
+		return -ERANGE;
+
+	/* Calculate the first and last logical blocks respectively. */
+	map.m_lblk = offset >> blkbits;
+	map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits,
+			  EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
+
+	ret = ext4_map_blocks(NULL, inode, &map, 0);
+	if (ret < 0)
+		return ret;
+
+	ext4_set_iomap(inode, iomap, &map, offset, length, flags);
 	return 0;
 }
 
-static void ext4_iomap_readahead(struct readahead_control *rac)
+const struct iomap_ops ext4_iomap_buffered_read_ops = {
+	.iomap_begin = ext4_iomap_buffered_read_begin,
+};
+
+static int ext4_iomap_read_folio(struct file *file, struct folio *folio)
 {
+	return iomap_read_folio(folio, &ext4_iomap_buffered_read_ops);
+}
 
+static void ext4_iomap_readahead(struct readahead_control *rac)
+{
+	iomap_readahead(rac, &ext4_iomap_buffered_read_ops);
 }
 
 static int ext4_iomap_writepages(struct address_space *mapping,
-- 
2.46.1