Description for this pull request:

- Replace the internal table lookup algorithm with the hweight library
     and ffs of the bitops library.
   - Handle the two types of stream entry, valid data size(has been written)
     and data size separately.It will improves compatibility with two
     differently sized files created on Windows.
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Merge tag 'exfat-for-6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/linkinjeon/exfat

Pull exfat updates from Namjae Jeon:

 - Replace the internal table lookup algorithm with the hweight library
   and ffs of the bitops library.

 - Handle the two types of stream entry, valid data size (has been
   written) and data size separately. It improves compatibility with two
   differently sized files created on Windows.

* tag 'exfat-for-6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/linkinjeon/exfat:
  exfat: do not zero the extended part
  exfat: change to get file size from DataLength
  exfat: using ffs instead of internal logic
  exfat: using hweight instead of internal logic

fs/exfat/balloc.c

@@ -5,42 +5,23 @@
 
 #include <linux/blkdev.h>
 #include <linux/slab.h>
+#include <linux/bitmap.h>
 #include <linux/buffer_head.h>
 
 #include "exfat_raw.h"
 #include "exfat_fs.h"
 
-static const unsigned char free_bit[] = {
+#if BITS_PER_LONG == 32
-	0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2,/*  0 ~  19*/
+#define __le_long __le32
-	0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 5, 0, 1, 0, 2, 0, 1, 0, 3,/* 20 ~  39*/
+#define lel_to_cpu(A) le32_to_cpu(A)
-	0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2,/* 40 ~  59*/
+#define cpu_to_lel(A) cpu_to_le32(A)
-	0, 1, 0, 6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4,/* 60 ~  79*/
+#elif BITS_PER_LONG == 64
-	0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 5, 0, 1, 0, 2,/* 80 ~  99*/
+#define __le_long __le64
-	0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3,/*100 ~ 119*/
+#define lel_to_cpu(A) le64_to_cpu(A)
-	0, 1, 0, 2, 0, 1, 0, 7, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2,/*120 ~ 139*/
+#define cpu_to_lel(A) cpu_to_le64(A)
-	0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 5,/*140 ~ 159*/
+#else
-	0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2,/*160 ~ 179*/
+#error "BITS_PER_LONG not 32 or 64"
-	0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 6, 0, 1, 0, 2, 0, 1, 0, 3,/*180 ~ 199*/
+#endif
-	0, 1, 0, 2, 0, 1, 0, 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2,/*200 ~ 219*/
-	0, 1, 0, 5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 4,/*220 ~ 239*/
-	0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0                /*240 ~ 254*/
-};
-
-static const unsigned char used_bit[] = {
-	0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, 1, 2, 2, 3,/*  0 ~  19*/
-	2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 1, 2, 2, 3, 2, 3, 3, 4,/* 20 ~  39*/
-	2, 3, 3, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5,/* 40 ~  59*/
-	4, 5, 5, 6, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,/* 60 ~  79*/
-	2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 2, 3, 3, 4,/* 80 ~  99*/
-	3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6,/*100 ~ 119*/
-	4, 5, 5, 6, 5, 6, 6, 7, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4,/*120 ~ 139*/
-	3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,/*140 ~ 159*/
-	2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5,/*160 ~ 179*/
-	4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 2, 3, 3, 4, 3, 4, 4, 5,/*180 ~ 199*/
-	3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6,/*200 ~ 219*/
-	5, 6, 6, 7, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,/*220 ~ 239*/
-	4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8             /*240 ~ 255*/
-};
 
 /*
  *  Allocation Bitmap Management Functions
@@ -200,32 +181,35 @@ unsigned int exfat_find_free_bitmap(struct super_block *sb, unsigned int clu)
 {
 	unsigned int i, map_i, map_b, ent_idx;
 	unsigned int clu_base, clu_free;
-	unsigned char k, clu_mask;
+	unsigned long clu_bits, clu_mask;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	__le_long bitval;
 
 	WARN_ON(clu < EXFAT_FIRST_CLUSTER);
-	ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
+	ent_idx = ALIGN_DOWN(CLUSTER_TO_BITMAP_ENT(clu), BITS_PER_LONG);
-	clu_base = BITMAP_ENT_TO_CLUSTER(ent_idx & ~(BITS_PER_BYTE_MASK));
+	clu_base = BITMAP_ENT_TO_CLUSTER(ent_idx);
 	clu_mask = IGNORED_BITS_REMAINED(clu, clu_base);
 
 	map_i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
 	map_b = BITMAP_OFFSET_BYTE_IN_SECTOR(sb, ent_idx);
 
 	for (i = EXFAT_FIRST_CLUSTER; i < sbi->num_clusters;
-	     i += BITS_PER_BYTE) {
+	     i += BITS_PER_LONG) {
-		k = *(sbi->vol_amap[map_i]->b_data + map_b);
+		bitval = *(__le_long *)(sbi->vol_amap[map_i]->b_data + map_b);
 		if (clu_mask > 0) {
-			k |= clu_mask;
+			bitval |= cpu_to_lel(clu_mask);
 			clu_mask = 0;
 		}
-		if (k < 0xFF) {
+		if (lel_to_cpu(bitval) != ULONG_MAX) {
-			clu_free = clu_base + free_bit[k];
+			clu_bits = lel_to_cpu(bitval);
+			clu_free = clu_base + ffz(clu_bits);
 			if (clu_free < sbi->num_clusters)
 				return clu_free;
 		}
-		clu_base += BITS_PER_BYTE;
+		clu_base += BITS_PER_LONG;
+		map_b += sizeof(long);
 
-		if (++map_b >= sb->s_blocksize ||
+		if (map_b >= sb->s_blocksize ||
 		    clu_base >= sbi->num_clusters) {
 			if (++map_i >= sbi->map_sectors) {
 				clu_base = EXFAT_FIRST_CLUSTER;
@@ -244,25 +228,24 @@ int exfat_count_used_clusters(struct super_block *sb, unsigned int *ret_count)
 	unsigned int count = 0;
 	unsigned int i, map_i = 0, map_b = 0;
 	unsigned int total_clus = EXFAT_DATA_CLUSTER_COUNT(sbi);
-	unsigned int last_mask = total_clus & BITS_PER_BYTE_MASK;
+	unsigned int last_mask = total_clus & (BITS_PER_LONG - 1);
-	unsigned char clu_bits;
+	unsigned long *bitmap, clu_bits;
-	const unsigned char last_bit_mask[] = {0, 0b00000001, 0b00000011,
-		0b00000111, 0b00001111, 0b00011111, 0b00111111, 0b01111111};
 
 	total_clus &= ~last_mask;
-	for (i = 0; i < total_clus; i += BITS_PER_BYTE) {
+	for (i = 0; i < total_clus; i += BITS_PER_LONG) {
-		clu_bits = *(sbi->vol_amap[map_i]->b_data + map_b);
+		bitmap = (void *)(sbi->vol_amap[map_i]->b_data + map_b);
-		count += used_bit[clu_bits];
+		count += hweight_long(*bitmap);
-		if (++map_b >= (unsigned int)sb->s_blocksize) {
+		map_b += sizeof(long);
+		if (map_b >= (unsigned int)sb->s_blocksize) {
 			map_i++;
 			map_b = 0;
 		}
 	}
 
 	if (last_mask) {
-		clu_bits = *(sbi->vol_amap[map_i]->b_data + map_b);
+		bitmap = (void *)(sbi->vol_amap[map_i]->b_data + map_b);
-		clu_bits &= last_bit_mask[last_mask];
+		clu_bits = lel_to_cpu(*(__le_long *)bitmap);
-		count += used_bit[clu_bits];
+		count += hweight_long(clu_bits & BITMAP_LAST_WORD_MASK(last_mask));
 	}
 
 	*ret_count = count;

fs/exfat/exfat_fs.h

@@ -135,8 +135,7 @@ enum {
 #define BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent) (ent & BITS_PER_SECTOR_MASK(sb))
 #define BITMAP_OFFSET_BYTE_IN_SECTOR(sb, ent) \
 	((ent / BITS_PER_BYTE) & ((sb)->s_blocksize - 1))
-#define BITS_PER_BYTE_MASK	0x7
+#define IGNORED_BITS_REMAINED(clu, clu_base) ((1UL << ((clu) - (clu_base))) - 1)
-#define IGNORED_BITS_REMAINED(clu, clu_base) ((1 << ((clu) - (clu_base))) - 1)
 
 #define ES_ENTRY_NUM(name_len)	(ES_IDX_LAST_FILENAME(name_len) + 1)
 /* 19 entries = 1 file entry + 1 stream entry + 17 filename entries */
@@ -208,6 +207,7 @@ struct exfat_dir_entry {
 	unsigned char flags;
 	unsigned short attr;
 	loff_t size;
+	loff_t valid_size;
 	unsigned int num_subdirs;
 	struct timespec64 atime;
 	struct timespec64 mtime;
@@ -317,6 +317,7 @@ struct exfat_inode_info {
 	loff_t i_size_aligned;
 	/* on-disk position of directory entry or 0 */
 	loff_t i_pos;
+	loff_t valid_size;
 	/* hash by i_location */
 	struct hlist_node i_hash_fat;
 	/* protect bmap against truncate */

fs/exfat/file.c

@@ -11,37 +11,76 @@
 #include <linux/fsnotify.h>
 #include <linux/security.h>
 #include <linux/msdos_fs.h>
+#include <linux/writeback.h>
 
 #include "exfat_raw.h"
 #include "exfat_fs.h"
 
 static int exfat_cont_expand(struct inode *inode, loff_t size)
 {
-	struct address_space *mapping = inode->i_mapping;
+	int ret;
-	loff_t start = i_size_read(inode), count = size - i_size_read(inode);
+	unsigned int num_clusters, new_num_clusters, last_clu;
-	int err, err2;
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	struct super_block *sb = inode->i_sb;
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	struct exfat_chain clu;
 
-	err = generic_cont_expand_simple(inode, size);
+	ret = inode_newsize_ok(inode, size);
-	if (err)
+	if (ret)
-		return err;
+		return ret;
 
+	num_clusters = EXFAT_B_TO_CLU_ROUND_UP(ei->i_size_ondisk, sbi);
+	new_num_clusters = EXFAT_B_TO_CLU_ROUND_UP(size, sbi);
+
+	if (new_num_clusters == num_clusters)
+		goto out;
+
+	exfat_chain_set(&clu, ei->start_clu, num_clusters, ei->flags);
+	ret = exfat_find_last_cluster(sb, &clu, &last_clu);
+	if (ret)
+		return ret;
+
+	clu.dir = (last_clu == EXFAT_EOF_CLUSTER) ?
+			EXFAT_EOF_CLUSTER : last_clu + 1;
+	clu.size = 0;
+	clu.flags = ei->flags;
+
+	ret = exfat_alloc_cluster(inode, new_num_clusters - num_clusters,
+			&clu, IS_DIRSYNC(inode));
+	if (ret)
+		return ret;
+
+	/* Append new clusters to chain */
+	if (clu.flags != ei->flags) {
+		exfat_chain_cont_cluster(sb, ei->start_clu, num_clusters);
+		ei->flags = ALLOC_FAT_CHAIN;
+	}
+	if (clu.flags == ALLOC_FAT_CHAIN)
+		if (exfat_ent_set(sb, last_clu, clu.dir))
+			goto free_clu;
+
+	if (num_clusters == 0)
+		ei->start_clu = clu.dir;
+
+out:
 	inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
+	/* Expanded range not zeroed, do not update valid_size */
+	i_size_write(inode, size);
+
+	ei->i_size_aligned = round_up(size, sb->s_blocksize);
+	ei->i_size_ondisk = ei->i_size_aligned;
+	inode->i_blocks = round_up(size, sbi->cluster_size) >> 9;
+
+	if (IS_DIRSYNC(inode))
+		return write_inode_now(inode, 1);
+
 	mark_inode_dirty(inode);
 
-	if (!IS_SYNC(inode))
 	return 0;
 
-	err = filemap_fdatawrite_range(mapping, start, start + count - 1);
+free_clu:
-	err2 = sync_mapping_buffers(mapping);
+	exfat_free_cluster(inode, &clu);
-	if (!err)
+	return -EIO;
-		err = err2;
-	err2 = write_inode_now(inode, 1);
-	if (!err)
-		err = err2;
-	if (err)
-		return err;
-
-	return filemap_fdatawait_range(mapping, start, start + count - 1);
 }
 
 static bool exfat_allow_set_time(struct exfat_sb_info *sbi, struct inode *inode)
@@ -146,6 +185,9 @@ int __exfat_truncate(struct inode *inode)
 		ei->start_clu = EXFAT_EOF_CLUSTER;
 	}
 
+	if (i_size_read(inode) < ei->valid_size)
+		ei->valid_size = i_size_read(inode);
+
 	if (ei->type == TYPE_FILE)
 		ei->attr |= EXFAT_ATTR_ARCHIVE;
 
@@ -474,15 +516,124 @@ int exfat_file_fsync(struct file *filp, loff_t start, loff_t end, int datasync)
 	return blkdev_issue_flush(inode->i_sb->s_bdev);
 }
 
+static int exfat_file_zeroed_range(struct file *file, loff_t start, loff_t end)
+{
+	int err;
+	struct inode *inode = file_inode(file);
+	struct address_space *mapping = inode->i_mapping;
+	const struct address_space_operations *ops = mapping->a_ops;
+
+	while (start < end) {
+		u32 zerofrom, len;
+		struct page *page = NULL;
+
+		zerofrom = start & (PAGE_SIZE - 1);
+		len = PAGE_SIZE - zerofrom;
+		if (start + len > end)
+			len = end - start;
+
+		err = ops->write_begin(file, mapping, start, len, &page, NULL);
+		if (err)
+			goto out;
+
+		zero_user_segment(page, zerofrom, zerofrom + len);
+
+		err = ops->write_end(file, mapping, start, len, len, page, NULL);
+		if (err < 0)
+			goto out;
+		start += len;
+
+		balance_dirty_pages_ratelimited(mapping);
+		cond_resched();
+	}
+
+out:
+	return err;
+}
+
+static ssize_t exfat_file_write_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	ssize_t ret;
+	struct file *file = iocb->ki_filp;
+	struct inode *inode = file_inode(file);
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	loff_t pos = iocb->ki_pos;
+	loff_t valid_size;
+
+	inode_lock(inode);
+
+	valid_size = ei->valid_size;
+
+	ret = generic_write_checks(iocb, iter);
+	if (ret < 0)
+		goto unlock;
+
+	if (pos > valid_size) {
+		ret = exfat_file_zeroed_range(file, valid_size, pos);
+		if (ret < 0 && ret != -ENOSPC) {
+			exfat_err(inode->i_sb,
+				"write: fail to zero from %llu to %llu(%zd)",
+				valid_size, pos, ret);
+		}
+		if (ret < 0)
+			goto unlock;
+	}
+
+	ret = __generic_file_write_iter(iocb, iter);
+	if (ret < 0)
+		goto unlock;
+
+	inode_unlock(inode);
+
+	if (pos > valid_size)
+		pos = valid_size;
+
+	if (iocb_is_dsync(iocb) && iocb->ki_pos > pos) {
+		ssize_t err = vfs_fsync_range(file, pos, iocb->ki_pos - 1,
+				iocb->ki_flags & IOCB_SYNC);
+		if (err < 0)
+			return err;
+	}
+
+	return ret;
+
+unlock:
+	inode_unlock(inode);
+
+	return ret;
+}
+
+static int exfat_file_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	int ret;
+	struct inode *inode = file_inode(file);
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	loff_t start = ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
+	loff_t end = min_t(loff_t, i_size_read(inode),
+			start + vma->vm_end - vma->vm_start);
+
+	if ((vma->vm_flags & VM_WRITE) && ei->valid_size < end) {
+		ret = exfat_file_zeroed_range(file, ei->valid_size, end);
+		if (ret < 0) {
+			exfat_err(inode->i_sb,
+				  "mmap: fail to zero from %llu to %llu(%d)",
+				  start, end, ret);
+			return ret;
+		}
+	}
+
+	return generic_file_mmap(file, vma);
+}
+
 const struct file_operations exfat_file_operations = {
 	.llseek		= generic_file_llseek,
 	.read_iter	= generic_file_read_iter,
-	.write_iter	= generic_file_write_iter,
+	.write_iter	= exfat_file_write_iter,
 	.unlocked_ioctl = exfat_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl = exfat_compat_ioctl,
 #endif
-	.mmap		= generic_file_mmap,
+	.mmap		= exfat_file_mmap,
 	.fsync		= exfat_file_fsync,
 	.splice_read	= filemap_splice_read,
 	.splice_write	= iter_file_splice_write,

fs/exfat/inode.c

@@ -75,8 +75,17 @@ int __exfat_write_inode(struct inode *inode, int sync)
 	if (ei->start_clu == EXFAT_EOF_CLUSTER)
 		on_disk_size = 0;
 
-	ep2->dentry.stream.valid_size = cpu_to_le64(on_disk_size);
+	ep2->dentry.stream.size = cpu_to_le64(on_disk_size);
-	ep2->dentry.stream.size = ep2->dentry.stream.valid_size;
+	/*
+	 * mmap write does not use exfat_write_end(), valid_size may be
+	 * extended to the sector-aligned length in exfat_get_block().
+	 * So we need to fixup valid_size to the writren length.
+	 */
+	if (on_disk_size < ei->valid_size)
+		ep2->dentry.stream.valid_size = ep2->dentry.stream.size;
+	else
+		ep2->dentry.stream.valid_size = cpu_to_le64(ei->valid_size);
+
 	if (on_disk_size) {
 		ep2->dentry.stream.flags = ei->flags;
 		ep2->dentry.stream.start_clu = cpu_to_le32(ei->start_clu);
@@ -278,6 +287,7 @@ static int exfat_get_block(struct inode *inode, sector_t iblock,
 	unsigned int cluster, sec_offset;
 	sector_t last_block;
 	sector_t phys = 0;
+	sector_t valid_blks;
 	loff_t pos;
 
 	mutex_lock(&sbi->s_lock);
@@ -306,17 +316,32 @@ static int exfat_get_block(struct inode *inode, sector_t iblock,
 	mapped_blocks = sbi->sect_per_clus - sec_offset;
 	max_blocks = min(mapped_blocks, max_blocks);
 
-	/* Treat newly added block / cluster */
-	if (iblock < last_block)
-		create = 0;
-
-	if (create || buffer_delay(bh_result)) {
 	pos = EXFAT_BLK_TO_B((iblock + 1), sb);
+	if ((create && iblock >= last_block) || buffer_delay(bh_result)) {
 		if (ei->i_size_ondisk < pos)
 			ei->i_size_ondisk = pos;
 	}
 
+	map_bh(bh_result, sb, phys);
+	if (buffer_delay(bh_result))
+		clear_buffer_delay(bh_result);
+
 	if (create) {
+		valid_blks = EXFAT_B_TO_BLK_ROUND_UP(ei->valid_size, sb);
+
+		if (iblock + max_blocks < valid_blks) {
+			/* The range has been written, map it */
+			goto done;
+		} else if (iblock < valid_blks) {
+			/*
+			 * The range has been partially written,
+			 * map the written part.
+			 */
+			max_blocks = valid_blks - iblock;
+			goto done;
+		}
+
+		/* The area has not been written, map and mark as new. */
 		err = exfat_map_new_buffer(ei, bh_result, pos);
 		if (err) {
 			exfat_fs_error(sb,
@@ -324,11 +349,58 @@ static int exfat_get_block(struct inode *inode, sector_t iblock,
 					pos, ei->i_size_aligned);
 			goto unlock_ret;
 		}
-	}
 
-	if (buffer_delay(bh_result))
+		ei->valid_size = EXFAT_BLK_TO_B(iblock + max_blocks, sb);
-		clear_buffer_delay(bh_result);
+		mark_inode_dirty(inode);
-	map_bh(bh_result, sb, phys);
+	} else {
+		valid_blks = EXFAT_B_TO_BLK(ei->valid_size, sb);
+
+		if (iblock + max_blocks < valid_blks) {
+			/* The range has been written, map it */
+			goto done;
+		} else if (iblock < valid_blks) {
+			/*
+			 * The area has been partially written,
+			 * map the written part.
+			 */
+			max_blocks = valid_blks - iblock;
+			goto done;
+		} else if (iblock == valid_blks &&
+			   (ei->valid_size & (sb->s_blocksize - 1))) {
+			/*
+			 * The block has been partially written,
+			 * zero the unwritten part and map the block.
+			 */
+			loff_t size, off;
+
+			max_blocks = 1;
+
+			/*
+			 * For direct read, the unwritten part will be zeroed in
+			 * exfat_direct_IO()
+			 */
+			if (!bh_result->b_folio)
+				goto done;
+
+			pos -= sb->s_blocksize;
+			size = ei->valid_size - pos;
+			off = pos & (PAGE_SIZE - 1);
+
+			folio_set_bh(bh_result, bh_result->b_folio, off);
+			err = bh_read(bh_result, 0);
+			if (err < 0)
+				goto unlock_ret;
+
+			folio_zero_segment(bh_result->b_folio, off + size,
+					off + sb->s_blocksize);
+		} else {
+			/*
+			 * The range has not been written, clear the mapped flag
+			 * to only zero the cache and do not read from disk.
+			 */
+			clear_buffer_mapped(bh_result);
+		}
+	}
 done:
 	bh_result->b_size = EXFAT_BLK_TO_B(max_blocks, sb);
 unlock_ret:
@@ -343,6 +415,17 @@ static int exfat_read_folio(struct file *file, struct folio *folio)
 
 static void exfat_readahead(struct readahead_control *rac)
 {
+	struct address_space *mapping = rac->mapping;
+	struct inode *inode = mapping->host;
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	loff_t pos = readahead_pos(rac);
+
+	/* Range cross valid_size, read it page by page. */
+	if (ei->valid_size < i_size_read(inode) &&
+	    pos <= ei->valid_size &&
+	    ei->valid_size < pos + readahead_length(rac))
+		return;
+
 	mpage_readahead(rac, exfat_get_block);
 }
 
@@ -370,9 +453,7 @@ static int exfat_write_begin(struct file *file, struct address_space *mapping,
 	int ret;
 
 	*pagep = NULL;
-	ret = cont_write_begin(file, mapping, pos, len, pagep, fsdata,
+	ret = block_write_begin(mapping, pos, len, pagep, exfat_get_block);
-			       exfat_get_block,
-			       &EXFAT_I(mapping->host)->i_size_ondisk);
 
 	if (ret < 0)
 		exfat_write_failed(mapping, pos+len);
@@ -400,6 +481,11 @@ static int exfat_write_end(struct file *file, struct address_space *mapping,
 	if (err < len)
 		exfat_write_failed(mapping, pos+len);
 
+	if (!(err < 0) && pos + err > ei->valid_size) {
+		ei->valid_size = pos + err;
+		mark_inode_dirty(inode);
+	}
+
 	if (!(err < 0) && !(ei->attr & EXFAT_ATTR_ARCHIVE)) {
 		inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
 		ei->attr |= EXFAT_ATTR_ARCHIVE;
@@ -413,6 +499,8 @@ static ssize_t exfat_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 {
 	struct address_space *mapping = iocb->ki_filp->f_mapping;
 	struct inode *inode = mapping->host;
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	loff_t pos = iocb->ki_pos;
 	loff_t size = iocb->ki_pos + iov_iter_count(iter);
 	int rw = iov_iter_rw(iter);
 	ssize_t ret;
@@ -436,8 +524,21 @@ static ssize_t exfat_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 	 * condition of exfat_get_block() and ->truncate().
 	 */
 	ret = blockdev_direct_IO(iocb, inode, iter, exfat_get_block);
-	if (ret < 0 && (rw & WRITE))
+	if (ret < 0) {
+		if (rw == WRITE)
 			exfat_write_failed(mapping, size);
+
+		if (ret != -EIOCBQUEUED)
+			return ret;
+	} else
+		size = pos + ret;
+
+	/* zero the unwritten part in the partially written block */
+	if (rw == READ && pos < ei->valid_size && ei->valid_size < size) {
+		iov_iter_revert(iter, size - ei->valid_size);
+		iov_iter_zero(size - ei->valid_size, iter);
+	}
+
 	return ret;
 }
 
@@ -537,6 +638,7 @@ static int exfat_fill_inode(struct inode *inode, struct exfat_dir_entry *info)
 	ei->start_clu = info->start_clu;
 	ei->flags = info->flags;
 	ei->type = info->type;
+	ei->valid_size = info->valid_size;
 
 	ei->version = 0;
 	ei->hint_stat.eidx = 0;

fs/exfat/namei.c

@@ -406,6 +406,7 @@ static int exfat_find_empty_entry(struct inode *inode,
 		i_size_write(inode, size);
 		ei->i_size_ondisk += sbi->cluster_size;
 		ei->i_size_aligned += sbi->cluster_size;
+		ei->valid_size += sbi->cluster_size;
 		ei->flags = p_dir->flags;
 		inode->i_blocks += sbi->cluster_size >> 9;
 	}
@@ -558,6 +559,8 @@ static int exfat_add_entry(struct inode *inode, const char *path,
 		info->size = clu_size;
 		info->num_subdirs = EXFAT_MIN_SUBDIR;
 	}
+	info->valid_size = info->size;
+
 	memset(&info->crtime, 0, sizeof(info->crtime));
 	memset(&info->mtime, 0, sizeof(info->mtime));
 	memset(&info->atime, 0, sizeof(info->atime));
@@ -660,6 +663,8 @@ static int exfat_find(struct inode *dir, struct qstr *qname,
 	info->type = exfat_get_entry_type(ep);
 	info->attr = le16_to_cpu(ep->dentry.file.attr);
 	info->size = le64_to_cpu(ep2->dentry.stream.valid_size);
+	info->valid_size = le64_to_cpu(ep2->dentry.stream.valid_size);
+	info->size = le64_to_cpu(ep2->dentry.stream.size);
 	if (info->size == 0) {
 		info->flags = ALLOC_NO_FAT_CHAIN;
 		info->start_clu = EXFAT_EOF_CLUSTER;
@@ -1288,6 +1293,7 @@ static int __exfat_rename(struct inode *old_parent_inode,
 			}
 
 			i_size_write(new_inode, 0);
+			new_ei->valid_size = 0;
 			new_ei->start_clu = EXFAT_EOF_CLUSTER;
 			new_ei->flags = ALLOC_NO_FAT_CHAIN;
 		}