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

[Keith Busch]

On Mon, Jul 14, 2025 at 03:17:13PM +0200, Christoph Hellwig wrote:
> Is is just me, or would it be a good idea to require an explicit
> opt-in to user hardware atomics?

IMO, if the block device's limits reports atomic capabilities, it's fair
game for any in kernel use. These are used outside of filesystems too,
like through raw block fops.

We've already settled on discarding problematic nvme attributes from
consideration. Is there something beyond that you've really found? If
so, maybe we should continue down the path of splitting more queue
limits into "hardware" and "user" values, and make filesystems subscribe
to the udev value where it defaults to "unsupported" for untrusted
devices.