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 left overs in
the holes in the merkle tree and past fsverity descriptor.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
---
 fs/xfs/xfs_fsverity.c | 67 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)

diff --git a/fs/xfs/xfs_fsverity.c b/fs/xfs/xfs_fsverity.c
index 5a6a48fcf843..b193009a1bdb 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>
@@ -173,6 +175,63 @@ 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;
+
+
+	while (offset_fsb < end_fsb) {
+		nimaps = 1;
+
+		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0,
+				0, &tp);
+		if (error)
+			return error;
+
+		xfs_ilock(ip, XFS_ILOCK_EXCL);
+		error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
+				&imap, &nimaps, 0);
+		if (error)
+			goto out_cancel;
+
+		if (nimaps == 0)
+			goto out_cancel;
+
+		if (imap.br_state == XFS_EXT_UNWRITTEN) {
+			xfs_trans_ijoin(tp, ip, 0);
+
+			error = xfs_bunmapi(tp, ip, imap.br_startoff,
+					imap.br_blockcount, 0, 1, &done);
+			if (error)
+				goto out_cancel;
+
+			error = xfs_trans_commit(tp);
+		} else {
+			xfs_trans_cancel(tp);
+		}
+		xfs_iunlock(ip, XFS_ILOCK_EXCL);
+
+		offset_fsb = imap.br_startoff + imap.br_blockcount;
+	}
+
+	return error;
+out_cancel:
+	xfs_trans_cancel(tp);
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	return error;
+}
+
 
 /*
  * Prepare to enable fsverity by clearing old metadata.
@@ -248,6 +307,14 @@ xfs_fsverity_end_enable(
 	if (error)
 		goto out;
 
+	/*
+	 * Remove unwritten extents left by COW preallocations and write
+	 * preallocation in the merkle tree holes and past descriptor
+	 */
+	error = xfs_fsverity_cancel_unwritten(ip, range_start, LLONG_MAX);
+	if (error)
+		goto out;
+
 	/*
 	 * Proactively drop any delayed allocations in COW fork, the fsverity
 	 * files are read-only
-- 
2.51.2