[PATCH RFC 4/4] xfs: fill dirty folios on zero range of unwritten mappings

[Brian Foster <bfoster@redhat.com>]

Use the iomap folio batch mechanism to identify which folios to zero
on zero range of unwritten mappings. Trim the resulting mapping if
the batch is filled (unlikely) and set the HAS_FOLIOS flag to inform
iomap that pagecache has been checked for dirty folios.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/xfs_iomap.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index ed42a28973bb..d84b7abf540c 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1037,6 +1037,15 @@ xfs_buffered_write_iomap_begin(
 				goto convert_delay;
 			if (end_fsb > eof_fsb)
 				end_fsb = eof_fsb;
+		} else if (imap.br_state == XFS_EXT_UNWRITTEN) {
+			u64 end;
+
+			xfs_trim_extent(&imap, offset_fsb, end_fsb - offset_fsb);
+			end = iomap_fill_dirty_folios(VFS_I(ip), iomap,
+					XFS_FSB_TO_B(mp, imap.br_startoff),
+					XFS_FSB_TO_B(mp, imap.br_blockcount));
+			end_fsb = min_t(xfs_fileoff_t, end_fsb, XFS_B_TO_FSB(mp, end));
+			iomap_flags |= IOMAP_F_HAS_FOLIOS;
 		}
 		xfs_trim_extent(&imap, offset_fsb, end_fsb - offset_fsb);
 	}
-- 
2.47.0