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

Jens Axboe
2024-12-12T19:42:58Z

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