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

On Tue, Jul 15, 2025 at 12:02:06PM +0200, Christian Brauner wrote:

quoted

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.

If we were to make this a mount option it would be really really ugly.
Either it is a filesystem specific mount option and then we have the
problem that we're ending up with different mount option names
per-filesystem.

Not that I'm arguing for a mount option (this should be sticky), but
we've had plenty of fs parsed mount options with common semantics.

It feels like this is something that needs to be done on the block
layer. IOW, maybe add generic block layer ioctls or a per-device sysfs
entry that allows to turn atomic writes on or off. That information
would then also potentially available to the filesystem to e.g.,
generate an info message during mount that hardware atomics are used or
aren't used. Because ultimately the block layer is where the decision
needs to be made.

The block layer just passes things through.