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

This patch starts support for iomap in the buffered I/O path of ext4
regular files. First, it introduces a new iomap address space operation,
ext4_iomap_aops. Additionally, it adds an inode state flag,
EXT4_STATE_BUFFERED_IOMAP, which indicates that the inode uses the iomap
path instead of the original buffer_head path for buffered I/O. Most
callbacks of ext4_iomap_aops can directly utilize generic
implementations, the remaining functions .read_folio(), .readahead(),
and .writepages() will be implemented in later patches.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/ext4/ext4.h  |  1 +
 fs/ext4/inode.c | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 44f6867d3037..ee170196bfff 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1916,6 +1916,7 @@ enum {
 	EXT4_STATE_VERITY_IN_PROGRESS,	/* building fs-verity Merkle tree */
 	EXT4_STATE_FC_COMMITTING,	/* Fast commit ongoing */
 	EXT4_STATE_ORPHAN_FILE,		/* Inode orphaned in orphan file */
+	EXT4_STATE_BUFFERED_IOMAP,	/* Inode use iomap for buffered IO */
 };
 
 #define EXT4_INODE_BIT_FNS(name, field, offset)				\
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 1ccf84a64b7b..b233f36efefa 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3526,6 +3526,22 @@ 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)
+{
+	return 0;
+}
+
+static void ext4_iomap_readahead(struct readahead_control *rac)
+{
+
+}
+
+static int ext4_iomap_writepages(struct address_space *mapping,
+				 struct writeback_control *wbc)
+{
+	return 0;
+}
+
 /*
  * For data=journal mode, folio should be marked dirty only when it was
  * writeably mapped. When that happens, it was already attached to the
@@ -3612,6 +3628,20 @@ static const struct address_space_operations ext4_da_aops = {
 	.swap_activate		= ext4_iomap_swap_activate,
 };
 
+static const struct address_space_operations ext4_iomap_aops = {
+	.read_folio		= ext4_iomap_read_folio,
+	.readahead		= ext4_iomap_readahead,
+	.writepages		= ext4_iomap_writepages,
+	.dirty_folio		= iomap_dirty_folio,
+	.bmap			= ext4_bmap,
+	.invalidate_folio	= iomap_invalidate_folio,
+	.release_folio		= iomap_release_folio,
+	.migrate_folio		= filemap_migrate_folio,
+	.is_partially_uptodate  = iomap_is_partially_uptodate,
+	.error_remove_folio	= generic_error_remove_folio,
+	.swap_activate		= ext4_iomap_swap_activate,
+};
+
 static const struct address_space_operations ext4_dax_aops = {
 	.writepages		= ext4_dax_writepages,
 	.dirty_folio		= noop_dirty_folio,
@@ -3633,6 +3663,8 @@ void ext4_set_aops(struct inode *inode)
 	}
 	if (IS_DAX(inode))
 		inode->i_mapping->a_ops = &ext4_dax_aops;
+	else if (ext4_test_inode_state(inode, EXT4_STATE_BUFFERED_IOMAP))
+		inode->i_mapping->a_ops = &ext4_iomap_aops;
 	else if (test_opt(inode->i_sb, DELALLOC))
 		inode->i_mapping->a_ops = &ext4_da_aops;
 	else
-- 
2.46.1