Re: [PATCH 07/12] fs: add RWF_UNCACHED iocb and FOP_UNCACHED file_operations flag

[Christoph Hellwig]

On Tue, Dec 03, 2024 at 08:31:43AM -0700, Jens Axboe wrote:
> +	if (flags & RWF_UNCACHED) {
> +		/* file system must support it */
> +		if (!(ki->ki_filp->f_op->fop_flags & FOP_UNCACHED))
> +			return -EOPNOTSUPP;
> +		/* DAX mappings not supported */
> +		if (IS_DAX(ki->ki_filp->f_mapping->host))
> +			return -EOPNOTSUPP;

I'd argue that DAX is always uncached and could just ignore the flag.
Same for direct I/O.