fs: remove power of 2 and length boundary atomic write restrictions

generic_atomic_write_valid() returns EINVAL for non-power-of-2 and for
non-length-aligned writes. This check is used for block devices, ext4
and xfs, but neither ext4 nor xfs rely on power of 2 restrictions.

For block devices, neither NVMe nor SCSI specification doesn't require
length alignment and 2^N length. Both specifications only require to
respect the atomic write boundary if it's set (NABSPF/NABO for NVMe and
ATOMIC BOUNDARY for SCSI). NVMe subsystem already checks writes against
this boundary; SCSI uses an explicit atomic write command so the write
is checked by the drive itself.

Signed-off-by: Vitaliy Filippov <[email protected]>

Author: Vitaliy Filippov

fs/read_write.c

@@ -1802,17 +1802,9 @@ int generic_file_rw_checks(struct file *file_in, struct file *file_out)
 
 int generic_atomic_write_valid(struct kiocb *iocb, struct iov_iter *iter)
 {
-	size_t len = iov_iter_count(iter);
-
 	if (!iter_is_ubuf(iter))
 		return -EINVAL;
 
-	if (!is_power_of_2(len))
-		return -EINVAL;
-
-	if (!IS_ALIGNED(iocb->ki_pos, len))
-		return -EINVAL;
-
 	if (!(iocb->ki_flags & IOCB_DIRECT))
 		return -EOPNOTSUPP;