Do we need an opt-in for file systems use of hw atomic writes?

[John Garry]

On 15/07/2025 07:02, Christoph Hellwig wrote:
> On Mon, Jul 14, 2025 at 04:53:49PM +0100, John Garry wrote:
>> I see. I figure that something like a FS_XFLAG could be used for that. But
>> we should still protect bdev fops users as well.
> 
> I'm not sure a XFLAG is all that useful.  It's not really a per-file
> persistent thing.  It's more of a mount option, or better persistent
> mount-option attr like we did for autofsck.

For all these options, the admin must know that the atomic behaviour of 
their disk is as advertised - I am not sure how realistic it is.

Apart from this, it would be nice to have an idea of how to handle the 
NVMe. About this:

" III.	 don't allow atomics on controllers that only report AWUPF and
  	 limit support to controllers that support that more sanely
	 defined NAWUPF"

Would it be possible to also have a driver opt-in for those controllers 
which don't support NAWUPF?

Thanks,
John