[RFC PATCH v4 29/34] ext4: fall back to buffer_head path for defrag

[Zhang Yi <yi.zhang@huaweicloud.com>]

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

Online defrag doesn't support iomap path yet, we have to fall back to
buffer_head path for the inode which has been using iomap. Changing
active inode is dangerous, before we start, we must hold the inode lock
and the mapping->invalidate_lock, and writeback all dirty folios and
drop the inode's pagecache.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/ext4/move_extent.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 7cd4afa4de1d..3db255385367 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -538,6 +538,34 @@ mext_check_arguments(struct inode *orig_inode,
 	return 0;
 }
 
+/*
+ * Disable buffered iomap path for the inode that requiring move extents,
+ * fallback to buffer_head path.
+ */
+static int ext4_disable_buffered_iomap_aops(struct inode *inode)
+{
+	int err;
+
+	/*
+	 * The buffered_head aops don't know how to handle folios
+	 * dirtied by iomap, so before falling back, flush all dirty
+	 * folios the inode has.
+	 */
+	filemap_invalidate_lock(inode->i_mapping);
+	err = filemap_write_and_wait(inode->i_mapping);
+	if (err < 0) {
+		filemap_invalidate_unlock(inode->i_mapping);
+		return err;
+	}
+	truncate_inode_pages(inode->i_mapping, 0);
+
+	ext4_clear_inode_state(inode, EXT4_STATE_BUFFERED_IOMAP);
+	ext4_set_aops(inode);
+	filemap_invalidate_unlock(inode->i_mapping);
+
+	return 0;
+}
+
 /**
  * ext4_move_extents - Exchange the specified range of a file
  *
@@ -609,6 +637,12 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
 	inode_dio_wait(orig_inode);
 	inode_dio_wait(donor_inode);
 
+	/* Fallback to buffer_head aops for inodes with buffered iomap aops */
+	if (ext4_test_inode_state(orig_inode, EXT4_STATE_BUFFERED_IOMAP))
+		ext4_disable_buffered_iomap_aops(orig_inode);
+	if (ext4_test_inode_state(donor_inode, EXT4_STATE_BUFFERED_IOMAP))
+		ext4_disable_buffered_iomap_aops(donor_inode);
+
 	/* Protect extent tree against block allocations via delalloc */
 	ext4_double_down_write_data_sem(orig_inode, donor_inode);
 	/* Check the filesystem environment whether move_extent can be done */
-- 
2.39.2