Re: [PATCH v3 08/11] exfat: add iomap buffered I/O support

[Chi Zhiling]

On 5/13/26 19:21, Namjae Jeon wrote:
> +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(sbi, cluster) + cluster_offset;
> +	iomap->type = IOMAP_MAPPED;
> +	if (may_alloc) {
> +		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 {
> +		if (offset >= ei->valid_size)
> +			iomap->type = IOMAP_UNWRITTEN;
> +
> +		if (iomap->type == IOMAP_MAPPED &&
> +		    iomap->offset < ei->valid_size &&
> +		    iomap->offset + iomap->length > ei->valid_size) {
> +			iomap->length = round_up(ei->valid_size,
> +						 i_blocksize(inode)) -
> +							iomap->offset;
> +		}

Hi, you can write it like this:

if (offset >= ei->valid_size) {
	iomap->type = IOMAP_UNWRITTEN;
} else if (offset + iomap->length > ei->valid_size) {
	iomap->length = round_up(ei->valid_size,
				 i_blocksize(inode)) -
					iomap->offset;
}

Thanks,