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

[Dave Chinner <david@fromorbit.com>]

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