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

[Jens Axboe]

On 12/10/24 4:22 AM, Christoph Hellwig wrote:
> 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.

It's more of a safe guard in terms of the invalidation requiring extra
work for DAX.

-- 
Jens Axboe