fs/ntfs3: check minimum alignment for direct I/O

Add a check for minimum alignment when performing direct I/O reads. If the
file offset or user buffer is not aligned to the device's logical block
size, fall back to buffered I/O instead of continuing with unaligned direct I/O.

Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

Author: aalexandrovich

fs/ntfs3/file.c

@@ -941,6 +941,16 @@ static ssize_t ntfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 		file->f_ra.ra_pages = 0;
 	}
 
+	/* Check minimum alignment for dio. */
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		struct super_block *sb = inode->i_sb;
+		struct ntfs_sb_info *sbi = sb->s_fs_info;
+		if ((iocb->ki_pos | iov_iter_alignment(iter)) &
+		    sbi->bdev_blocksize_mask) {
+			iocb->ki_flags &= ~IOCB_DIRECT;
+		}
+	}
+
 	return generic_file_read_iter(iocb, iter);
 }
 

fs/ntfs3/ntfs_fs.h

@@ -212,6 +212,7 @@ struct ntfs_sb_info {
 
 	u32 discard_granularity;
 	u64 discard_granularity_mask_inv; // ~(discard_granularity_mask_inv-1)
+	u32 bdev_blocksize_mask; // bdev_logical_block_size(bdev) - 1;
 
 	u32 cluster_size; // bytes per cluster
 	u32 cluster_mask; // == cluster_size - 1

fs/ntfs3/super.c

@@ -1075,6 +1075,7 @@ static int ntfs_init_from_boot(struct super_block *sb, u32 sector_size,
 		dev_size += sector_size - 1;
 	}
 
+	sbi->bdev_blocksize_mask = max(boot_sector_size, sector_size) - 1;
 	sbi->mft.lbo = mlcn << cluster_bits;
 	sbi->mft.lbo2 = mlcn2 << cluster_bits;