XFS preallocates spaces during writes. In normal I/O this space, if
unused, is removed by truncate. For files with fsverity, XFS does not
use truncate as fsverity metadata is stored past EOF.

After we're done with writing fsverity metadata iterate over extents in
that region and remove any unwritten ones. These would be preallocation
leftovers in the merkle tree holes and past fsverity descriptor.

Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
---
 fs/xfs/xfs_fsverity.c | 62 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/fs/xfs/xfs_fsverity.c b/fs/xfs/xfs_fsverity.c
index e5cd17ec15b6..f78e5f0c2fd0 100644
--- a/fs/xfs/xfs_fsverity.c
+++ b/fs/xfs/xfs_fsverity.c
@@ -21,6 +21,8 @@
 #include "xfs_iomap.h"
 #include "xfs_error.h"
 #include "xfs_health.h"
+#include "xfs_bmap.h"
+#include "xfs_bmap_util.h"
 #include <linux/fsverity.h>
 #include <linux/iomap.h>
 #include <linux/pagemap.h>
@@ -189,6 +191,58 @@ xfs_fsverity_delete_metadata(
 	return error;
 }
 
+static int
+xfs_fsverity_cancel_unwritten(
+	struct xfs_inode	*ip,
+	xfs_fileoff_t		start,
+	xfs_fileoff_t		end)
+{
+	struct xfs_mount	*mp = ip->i_mount;
+	struct xfs_trans	*tp;
+	xfs_fileoff_t		offset_fsb = XFS_B_TO_FSB(mp, start);
+	xfs_fileoff_t		end_fsb = XFS_B_TO_FSB(mp, end);
+	struct xfs_bmbt_irec	imap;
+	int			nimaps;
+	int			error = 0;
+	int			done;
+
+	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0, 0, &tp);
+	if (error)
+		return error;
+
+	xfs_ilock(ip, XFS_ILOCK_EXCL);
+	xfs_trans_ijoin(tp, ip, 0);
+
+	while (offset_fsb < end_fsb) {
+		nimaps = 1;
+
+		error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
+							  &imap, &nimaps, 0);
+		if (error)
+			goto out_cancel;
+
+		if (nimaps == 0)
+			break;
+
+		if (imap.br_state == XFS_EXT_UNWRITTEN) {
+			error = xfs_bunmapi(tp, ip, imap.br_startoff,
+					    imap.br_blockcount, 0, 1, &done);
+			if (error)
+				goto out_cancel;
+		}
+
+		offset_fsb = imap.br_startoff + imap.br_blockcount;
+	}
+
+	error = xfs_trans_commit(tp);
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	return error;
+out_cancel:
+	xfs_trans_cancel(tp);
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	return error;
+}
+
 
 /*
  * Prepare to enable fsverity by clearing old metadata.
@@ -264,6 +318,14 @@ xfs_fsverity_end_enable(
 	if (error)
 		goto out;
 
+	/*
+	 * Remove unwritten extents left by preallocations in the merkle tree
+	 * holes and past descriptor
+	 */
+	error = xfs_fsverity_cancel_unwritten(ip, range_start, LLONG_MAX);
+	if (error)
+		goto out;
+
 	/*
 	 * Set fsverity inode flag
 	 */
-- 
2.51.2