[PATCH -next v5 12/32] ext4: implement buffered read path using iomap

From: Zhang Yi <[email protected]>

Implement the iomap read path for ext4 by introducing a new
ext4_iomap_buffered_read_ops instance. This provides the read_folio()
and readahead() callbacks for ext4_iomap_aops. The implementation
introduces:

 - ext4_iomap_map_blocks(): Helper function to query extent mappings for
   a given read range using ext4_map_blocks() and convert the mapping
   information to iomap type
 - ext4_iomap_buffered_read_begin(): The iomap_begin callbacks that maps
   blocks, validates filesystem state, and populates the iomap. It
   returns -ERANGE for inline data which is not yet supported.

Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Reviewed-by: Ojaswin Mujoo <[email protected]>
---
 fs/ext4/inode.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index dda78cf1f68d..376cb9783835 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3956,14 +3956,60 @@ const struct iomap_ops ext4_iomap_report_ops = {
 	.iomap_next = ext4_iomap_next_report,
 };
 
+static int ext4_iomap_map_blocks(struct inode *inode, loff_t offset,
+		loff_t length, struct ext4_map_blocks *map)
+{
+	u8 blkbits = inode->i_blkbits;
+
+	if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
+		return -EINVAL;
+
+	/* 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;
+
+	return ext4_map_blocks(NULL, inode, map, 0);
+}
+
+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)
+{
+	struct ext4_map_blocks map;
+	int ret;
+
+	if (unlikely(ext4_forced_shutdown(inode->i_sb)))
+		return -EIO;
+
+	/* Inline data support is not yet available. */
+	if (WARN_ON_ONCE(ext4_has_inline_data(inode)))
+		return -ERANGE;
+
+	ret = ext4_iomap_map_blocks(inode, offset, length, &map);
+	if (ret < 0)
+		return ret;
+
+	ext4_set_iomap(inode, iomap, &map, offset, length, flags);
+	return 0;
+}
+
+static DEFINE_IOMAP_ITER_NEXT(ext4_iomap_buffered_read_next,
+			      ext4_iomap_buffered_read_begin);
+
+const struct iomap_ops ext4_iomap_buffered_read_ops = {
+	.iomap_next = ext4_iomap_buffered_read_next,
+};
+
 static int ext4_iomap_read_folio(struct file *file, struct folio *folio)
 {
+	iomap_bio_read_folio(folio, &ext4_iomap_buffered_read_ops);
 	return 0;
 }
 
 static void ext4_iomap_readahead(struct readahead_control *rac)
 {
-
+	iomap_bio_readahead(rac, &ext4_iomap_buffered_read_ops);
 }
 
 static int ext4_iomap_writepages(struct address_space *mapping,
-- 
2.52.0