1 files changed, 272 insertions, 0 deletions
diff --git a/fs/exfat/iomap.c b/fs/exfat/iomap.c
new file mode 100644
index 000000000..4b9207bc4
--- /dev/null
+++ b/fs/exfat/iomap.c
@@ -0,0 +1,272 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * iomap callack functions
+ *
+ * Copyright (C) 2026 Namjae Jeon <linkinjeon@kernel.org>
+ */
+
+#include <linux/iomap.h>
+#include <linux/pagemap.h>
+
+#include "exfat_raw.h"
+#include "exfat_fs.h"
+#include "iomap.h"
+
+/*
+ * exfat_file_write_dio_end_io - Direct I/O write completion handler
+ *
+ * Updates i_size if the write extended the file. Called from the dio layer
+ * after I/O completion.
+ */
+static int exfat_file_write_dio_end_io(struct kiocb *iocb, ssize_t size,
+		int error, unsigned int flags)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+
+	if (error)
+		return error;
+
+	if (size && i_size_read(inode) < iocb->ki_pos + size) {
+		i_size_write(inode, iocb->ki_pos + size);
+		mark_inode_dirty(inode);
+	}
+
+	return 0;
+}
+
+const struct iomap_dio_ops exfat_write_dio_ops = {
+	.end_io		= exfat_file_write_dio_end_io,
+};
+
+static int __exfat_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
+		unsigned int flags, struct iomap *iomap, bool may_alloc)
+{
+	struct super_block *sb = inode->i_sb;
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	unsigned int cluster, num_clusters;
+	loff_t cluster_offset, cluster_length;
+	int err;
+	bool balloc = false;
+
+	if (!may_alloc) {
+		/* Completely beyond EOF. Treat as hole */
+		if (i_size_read(inode) <= offset) {
+			iomap->type = IOMAP_HOLE;
+			iomap->addr = IOMAP_NULL_ADDR;
+			iomap->offset = offset;
+			iomap->length = length;
+			return 0;
+		}
+
+		/* Clamp length if the requested range goes beyond i_size */
+		if (offset + length > i_size_read(inode))
+			length = round_up(i_size_read(inode),
+					  i_blocksize(inode)) - offset;
+	}
+
+	num_clusters = exfat_bytes_to_cluster_round_up(sbi,
+			offset + length) - exfat_bytes_to_cluster(sbi, offset);
+
+	mutex_lock(&sbi->s_lock);
+	iomap->bdev = inode->i_sb->s_bdev;
+	iomap->offset = offset;
+
+	err = exfat_map_cluster(inode, exfat_bytes_to_cluster(sbi, offset),
+			&cluster, &num_clusters, may_alloc, &balloc);
+	if (err)
+		goto out;
+
+	cluster_offset = exfat_cluster_offset(sbi, offset);
+	cluster_length = exfat_cluster_to_bytes(sbi, num_clusters);
+
+	iomap->length = min_t(loff_t, length, cluster_length - cluster_offset);
+	iomap->addr = exfat_cluster_to_phys_bytes(sbi, cluster) + cluster_offset;
+	iomap->type = IOMAP_MAPPED;
+	iomap->flags = IOMAP_F_MERGED;
+
+	if (may_alloc || flags & IOMAP_ZERO) {
+		if (balloc)
+			iomap->flags |= IOMAP_F_NEW;
+		else if (iomap->offset + iomap->length >= ei->valid_size) {
+			/*
+			 * This is a write that starts at or extends beyond
+			 * the current valid_size. The region between the old
+			 * valid_size and the end of this write needs to be
+			 * zeroed in the page cache to prevent stale data
+			 * exposure (see IOMAP_F_ZERO_TAIL handling in
+			 * __iomap_write_begin()).
+			 */
+			iomap->flags |= IOMAP_F_ZERO_TAIL;
+		}
+	} else {
+		/*
+		 * valid_size is tracked in byte granularity and
+		 * marks the exact boundary between valid data and
+		 * holes (or unwritten space).
+		 *
+		 * When IOMAP_REPORT is set (used by lseek(SEEK_HOLE)
+		 * and SEEK_DATA), we return IOMAP_HOLE. This allows
+		 * iomap_seek_hole_iter() to directly return the
+		 * precise byte position.
+		 *
+		 * For normal I/O paths (without IOMAP_REPORT) we
+		 * return IOMAP_UNWRITTEN so the write path can
+		 * distinguish it from a real hole.
+		 */
+		if (offset >= ei->valid_size) {
+			iomap->type = flags & IOMAP_REPORT ?
+				IOMAP_HOLE : IOMAP_UNWRITTEN;
+		} else if (offset + iomap->length > ei->valid_size) {
+			if (flags & IOMAP_REPORT) {
+				/*
+				 * For SEEK_HOLE/SEEK_DATA, clip the length
+				 * to the exact byte boundary (valid_size).
+				 * This ensures the caller gets the precise
+				 * hole position in byte units.
+				 */
+				iomap->length = ei->valid_size - iomap->offset;
+			} else
+				iomap->length = round_up(ei->valid_size,
+							 i_blocksize(inode)) -
+								iomap->offset;
+		}
+	}
+
+	iomap->flags |= IOMAP_F_MERGED;
+out:
+	mutex_unlock(&sbi->s_lock);
+	return err;
+}
+
+static int exfat_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
+		unsigned int flags, struct iomap *iomap, struct iomap *srcmap)
+{
+	return __exfat_iomap_begin(inode, offset, length, flags, iomap, false);
+}
+
+static int exfat_write_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
+		unsigned int flags, struct iomap *iomap, struct iomap *srcmap)
+{
+	return __exfat_iomap_begin(inode, offset, length, flags, iomap, true);
+}
+
+static DEFINE_IOMAP_ITER_NEXT(exfat_iomap_next, exfat_iomap_begin);
+
+const struct iomap_ops exfat_iomap_ops = {
+	.iomap_next = exfat_iomap_next,
+};
+
+/*
+ * exfat_write_iomap_end - Update the state after write
+ *
+ * Extends ->valid_size to cover the newly written range.
+ * Marks the inode dirty if metadata was changed.
+ */
+static int exfat_write_iomap_end(struct inode *inode, loff_t pos, loff_t length,
+		ssize_t written, unsigned int flags, struct iomap *iomap)
+{
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	bool dirtied = false;
+	loff_t end;
+
+	if (!written)
+		return 0;
+
+	end = pos + written;
+
+	if (ei->valid_size < end) {
+		ei->valid_size = end;
+		if (ei->zeroed_size < end)
+			ei->zeroed_size = end;
+		dirtied = true;
+	}
+
+	if (dirtied || iomap->flags & IOMAP_F_SIZE_CHANGED)
+		mark_inode_dirty(inode);
+
+	return written;
+}
+
+static DEFINE_IOMAP_ITER_NEXT_END(exfat_write_iomap_next,
+		exfat_write_iomap_begin, exfat_write_iomap_end);
+
+const struct iomap_ops exfat_write_iomap_ops = {
+	.iomap_next	= exfat_write_iomap_next,
+};
+
+/*
+ * exfat_writeback_range - Map folio during writeback
+ *
+ * Called for each folio during writeback. If the folio falls outside the
+ * current iomap, remaps by calling read_iomap_begin.
+ */
+static ssize_t exfat_writeback_range(struct iomap_writepage_ctx *wpc,
+		struct folio *folio, u64 offset, unsigned int len, u64 end_pos)
+{
+	if (offset < wpc->iomap.offset ||
+	    offset >= wpc->iomap.offset + wpc->iomap.length) {
+		int error;
+
+		error = __exfat_iomap_begin(wpc->inode, offset, len,
+				0, &wpc->iomap, false);
+		if (error)
+			return error;
+	}
+
+	return iomap_add_to_ioend(wpc, folio, offset, end_pos, len);
+}
+
+const struct iomap_writeback_ops exfat_writeback_ops = {
+	.writeback_range	= exfat_writeback_range,
+	.writeback_submit	= iomap_ioend_writeback_submit,
+};
+
+/**
+ * exfat_iomap_read_end_io - iomap read bio completion handler for exFAT
+ * @bio: bio that has completed reading
+ *
+ * exfat_iomap_begin() rounds up MAPPED extents to the block boundary of
+ * valid_size. This ensures that any subsequent blocks are treated as
+ * IOMAP_UNWRITTEN, but it also causes the "straddle block" containing
+ * valid_size to be read from disk. The disk data beyond valid_size in
+ * this block is stale and must be zeroed to prevent data leakage.
+ */
+static void exfat_iomap_read_end_io(struct bio *bio)
+{
+	int error = blk_status_to_errno(bio->bi_status);
+	struct folio_iter iter;
+
+	bio_for_each_folio_all(iter, bio) {
+		struct folio *folio = iter.folio;
+		struct exfat_inode_info *ei = EXFAT_I(folio->mapping->host);
+		s64 valid_size;
+		loff_t pos = folio_pos(folio);
+
+		valid_size = ei->valid_size;
+		if (pos + iter.offset < valid_size &&
+		    pos + iter.offset + iter.length > valid_size)
+			folio_zero_segment(folio, offset_in_folio(folio, valid_size),
+					   iter.offset + iter.length);
+
+		iomap_finish_folio_read(folio, iter.offset, iter.length, error);
+	}
+	bio_put(bio);
+}
+
+static void exfat_iomap_bio_submit_read(const struct iomap_iter *iter,
+		struct iomap_read_folio_ctx *ctx)
+{
+	iomap_bio_submit_read_endio(iter, ctx, exfat_iomap_read_end_io);
+}
+
+const struct iomap_read_ops exfat_iomap_bio_read_ops = {
+	.read_folio_range	= iomap_bio_read_folio_range,
+	.submit_read		= exfat_iomap_bio_submit_read,
+};
+
+int exfat_iomap_swap_activate(struct swap_info_struct *sis,
+			       struct file *file, sector_t *span)
+{
+	return iomap_swapfile_activate(sis, file, span, &exfat_iomap_ops);
+}