3 files changed, 72 insertions, 39 deletions

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 91ee0b308e13..734b761a1e4a 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -832,6 +832,66 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
 }
 EXPORT_SYMBOL_GPL(iomap_file_buffered_write);
 
+/*
+ * When a short write occurs, the filesystem may need to remove reserved space
+ * that was allocated in ->iomap_begin from it's ->iomap_end method. For
+ * filesystems that use delayed allocation, we need to punch out delalloc
+ * extents from the range that are not dirty in the page cache. As the write can
+ * race with page faults, there can be dirty pages over the delalloc extent
+ * outside the range of a short write but still within the delalloc extent
+ * allocated for this iomap.
+ *
+ * This function uses [start_byte, end_byte) intervals (i.e. open ended) to
+ * simplify range iterations, but converts them back to {offset,len} tuples for
+ * the punch callback.
+ */
+int iomap_file_buffered_write_punch_delalloc(struct inode *inode,
+		struct iomap *iomap, loff_t pos, loff_t length,
+		ssize_t written,
+		int (*punch)(struct inode *inode, loff_t pos, loff_t length))
+{
+	loff_t			start_byte;
+	loff_t			end_byte;
+	int			blocksize = i_blocksize(inode);
+	int			error = 0;
+
+	if (iomap->type != IOMAP_DELALLOC)
+		return 0;
+
+	/* If we didn't reserve the blocks, we're not allowed to punch them. */
+	if (!(iomap->flags & IOMAP_F_NEW))
+		return 0;
+
+	/*
+	 * start_byte refers to the first unused block after a short write. If
+	 * nothing was written, round offset down to point at the first block in
+	 * the range.
+	 */
+	if (unlikely(!written))
+		start_byte = round_down(pos, blocksize);
+	else
+		start_byte = round_up(pos + written, blocksize);
+	end_byte = round_up(pos + length, blocksize);
+
+	/* Nothing to do if we've written the entire delalloc extent */
+	if (start_byte >= end_byte)
+		return 0;
+
+	/*
+	 * Lock the mapping to avoid races with page faults re-instantiating
+	 * folios and dirtying them via ->page_mkwrite between the page cache
+	 * truncation and the delalloc extent removal. Failing to do this can
+	 * leave dirty pages with no space reservation in the cache.
+	 */
+	filemap_invalidate_lock(inode->i_mapping);
+	truncate_pagecache_range(inode, start_byte, end_byte - 1);
+	error = punch(inode, start_byte, end_byte - start_byte);
+	filemap_invalidate_unlock(inode->i_mapping);
+
+	return error;
+}
+EXPORT_SYMBOL_GPL(iomap_file_buffered_write_punch_delalloc);
+
 static loff_t iomap_unshare_iter(struct iomap_iter *iter)
 {
 	struct iomap *iomap = &iter->iomap;
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 7bb55dbc19d3..ea96e8a34868 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1123,12 +1123,12 @@ out_unlock:
 static int
 xfs_buffered_write_delalloc_punch(
 	struct inode		*inode,
-	loff_t			start_byte,
-	loff_t			end_byte)
+	loff_t			offset,
+	loff_t			length)
 {
 	struct xfs_mount	*mp = XFS_M(inode->i_sb);
-	xfs_fileoff_t		start_fsb = XFS_B_TO_FSBT(mp, start_byte);
-	xfs_fileoff_t		end_fsb = XFS_B_TO_FSB(mp, end_byte);
+	xfs_fileoff_t		start_fsb = XFS_B_TO_FSBT(mp, offset);
+	xfs_fileoff_t		end_fsb = XFS_B_TO_FSB(mp, offset + length);
 
 	return xfs_bmap_punch_delalloc_range(XFS_I(inode), start_fsb,
 				end_fsb - start_fsb);
@@ -1143,13 +1143,9 @@ xfs_buffered_write_iomap_end(
 	unsigned		flags,
 	struct iomap		*iomap)
 {
-	struct xfs_mount	*mp = XFS_M(inode->i_sb);
-	loff_t			start_byte;
-	loff_t			end_byte;
-	int			error = 0;
 
-	if (iomap->type != IOMAP_DELALLOC)
-		return 0;
+	struct xfs_mount	*mp = XFS_M(inode->i_sb);
+	int			error;
 
 	/*
 	 * Behave as if the write failed if drop writes is enabled. Set the NEW
@@ -1160,35 +1156,8 @@ xfs_buffered_write_iomap_end(
 		written = 0;
 	}
 
-	/* If we didn't reserve the blocks, we're not allowed to punch them. */
-	if (!(iomap->flags & IOMAP_F_NEW))
-		return 0;
-
-	/*
-	 * start_fsb refers to the first unused block after a short write. If
-	 * nothing was written, round offset down to point at the first block in
-	 * the range.
-	 */
-	if (unlikely(!written))
-		start_byte = round_down(offset, mp->m_sb.sb_blocksize);
-	else
-		start_byte = round_up(offset + written, mp->m_sb.sb_blocksize);
-	end_byte = round_up(offset + length, mp->m_sb.sb_blocksize);
-
-	/* Nothing to do if we've written the entire delalloc extent */
-	if (start_byte >= end_byte)
-		return 0;
-
-	/*
-	 * Lock the mapping to avoid races with page faults re-instantiating
-	 * folios and dirtying them via ->page_mkwrite between the page cache
-	 * truncation and the delalloc extent removal. Failing to do this can
-	 * leave dirty pages with no space reservation in the cache.
-	 */
-	filemap_invalidate_lock(inode->i_mapping);
-	truncate_pagecache_range(inode, start_byte, end_byte - 1);
-	error = xfs_buffered_write_delalloc_punch(inode, start_byte, end_byte);
-	filemap_invalidate_unlock(inode->i_mapping);
+	error = iomap_file_buffered_write_punch_delalloc(inode, iomap, offset,
+			length, written, &xfs_buffered_write_delalloc_punch);
 	if (error && !xfs_is_shutdown(mp)) {
 		xfs_alert(mp, "%s: unable to clean up ino 0x%llx",
 			__func__, XFS_I(inode)->i_ino);
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 238a03087e17..0698c4b8ce0e 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -226,6 +226,10 @@ static inline const struct iomap *iomap_iter_srcmap(const struct iomap_iter *i)
 
 ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
 		const struct iomap_ops *ops);
+int iomap_file_buffered_write_punch_delalloc(struct inode *inode,
+		struct iomap *iomap, loff_t pos, loff_t length, ssize_t written,
+		int (*punch)(struct inode *inode, loff_t pos, loff_t length));
+
 int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops);
 void iomap_readahead(struct readahead_control *, const struct iomap_ops *ops);
 bool iomap_is_partially_uptodate(struct folio *, size_t from, size_t count);