Re: [PATCH v4 03/11] fs: Initial atomic write support

Dave Chinner
2024-02-19T22:44:17Z

On Mon, Feb 19, 2024 at 01:01:01PM +0000, John Garry wrote:
> @@ -3523,4 +3535,26 @@ extern int vfs_fadvise(struct file *file, loff_t offset, loff_t len,
> extern int generic_fadvise(struct file *file, loff_t offset, loff_t len,
> int advice);
>
> +static inline bool atomic_write_valid(loff_t pos, struct iov_iter *iter,
> + unsigned int unit_min, unsigned int unit_max)
> +{
> + size_t len = iov_iter_count(iter);
> +
> + if (!iter_is_ubuf(iter))
> + return false;
> +
> + if (len == unit_min || len == unit_max) {
> + /* ok if exactly min or max */
> + } else if (len < unit_min || len > unit_max) {
> + return false;
> + } else if (!is_power_of_2(len)) {
> + return false;
> + }

This doesn't need if else if else if and it doesn't need to check
for exact unit min/max matches. The exact matches require the
length to be a power of 2, so the checks are simply:

if (len < unit_min || len > unit_max)
return false;
if (!is_power_of_2(len))
return false;

> + if (pos & (len - 1))
> + return false;

This has typing issues - 64 bit value, 32 bit mask. probably should
use:

if (!IS_ALIGNED(pos, len))
return false;

-Dave.

--
Dave Chinner
david@fromorbit.com