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

Partially enable iomap for the buffered I/O path of regular files with
the default mount option. This supports default filesystem features and
the bigalloc feature. However, it does not yet support inline data,
fs_verity, fs_crypt, online defrag and data=journal mode. Some of these
features should be supported gradually in the future. The filesystem
will fallback to the buffered_head path automatically if these mount
options or features are enabled.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/ext4/ext4.h   |  1 +
 fs/ext4/ialloc.c |  3 +++
 fs/ext4/inode.c  | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index e1b7f7024f07..0096191b454c 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2987,6 +2987,7 @@ int ext4_walk_page_buffers(handle_t *handle,
 				     struct buffer_head *bh));
 int do_journal_get_write_access(handle_t *handle, struct inode *inode,
 				struct buffer_head *bh);
+bool ext4_should_use_buffered_iomap(struct inode *inode);
 int ext4_nonda_switch(struct super_block *sb);
 #define FALL_BACK_TO_NONDELALLOC 1
 #define CONVERT_INLINE_DATA	 2
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 7f1a5f90dbbd..2e3e257b9808 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -1333,6 +1333,9 @@ struct inode *__ext4_new_inode(struct mnt_idmap *idmap,
 		}
 	}
 
+	if (ext4_should_use_buffered_iomap(inode))
+		ext4_set_inode_state(inode, EXT4_STATE_BUFFERED_IOMAP);
+
 	ext4_update_inode_fsync_trans(handle, inode, 1);
 
 	err = ext4_mark_inode_dirty(handle, inode);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 50e4afd17e93..512094dc4117 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -776,6 +776,8 @@ static int _ext4_get_block(struct inode *inode, sector_t iblock,
 
 	if (ext4_has_inline_data(inode))
 		return -ERANGE;
+	if (WARN_ON(ext4_test_inode_state(inode, EXT4_STATE_BUFFERED_IOMAP)))
+		return -EINVAL;
 
 	map.m_lblk = iblock;
 	map.m_len = bh->b_size >> inode->i_blkbits;
@@ -2572,6 +2574,9 @@ static int ext4_do_writepages(struct mpage_da_data *mpd)
 
 	trace_ext4_writepages(inode, wbc);
 
+	if (WARN_ON(ext4_test_inode_state(inode, EXT4_STATE_BUFFERED_IOMAP)))
+		return -EINVAL;
+
 	/*
 	 * No pages to write? This is mainly a kludge to avoid starting
 	 * a transaction for special inodes like journal inode on last iput()
@@ -5144,6 +5149,30 @@ static const char *check_igot_inode(struct inode *inode, ext4_iget_flags flags)
 	return NULL;
 }
 
+bool ext4_should_use_buffered_iomap(struct inode *inode)
+{
+	struct super_block *sb = inode->i_sb;
+
+	if (ext4_has_feature_inline_data(sb))
+		return false;
+	if (ext4_has_feature_verity(sb))
+		return false;
+	if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA)
+		return false;
+	if (!S_ISREG(inode->i_mode))
+		return false;
+	if (IS_DAX(inode))
+		return false;
+	if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
+		return false;
+	if (ext4_test_inode_flag(inode, EXT4_INODE_EA_INODE))
+		return false;
+	if (ext4_test_inode_flag(inode, EXT4_INODE_ENCRYPT))
+		return false;
+
+	return true;
+}
+
 struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
 			  ext4_iget_flags flags, const char *function,
 			  unsigned int line)
@@ -5408,6 +5437,9 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
 	if (ret)
 		goto bad_inode;
 
+	if (ext4_should_use_buffered_iomap(inode))
+		ext4_set_inode_state(inode, EXT4_STATE_BUFFERED_IOMAP);
+
 	if (S_ISREG(inode->i_mode)) {
 		inode->i_op = &ext4_file_inode_operations;
 		inode->i_fop = &ext4_file_operations;
-- 
2.46.1