Re: [PATCH V5 00/12] Enable per-file/per-directory DAX operations V5

[Christoph Hellwig]

On Wed, Apr 01, 2020 at 12:25:11PM +0200, Jan Kara wrote:
> >  - Applications must call statx to discover the current S_DAX state.
> > 
> >  - There exists an advisory file inode flag FS_XFLAG_DAX that can be
> >    changed on files that have no blocks allocated to them.  Changing
> >    this flag does not necessarily change the S_DAX state immediately
> >    but programs can query the S_DAX state via statx.
> 
> I generally like the proposal but I think the fact that toggling
> FS_XFLAG_DAX will not have immediate effect on S_DAX will cause quite some
> confusion and ultimately bug reports. I'm thinking whether we could somehow
> improve this... For example an ioctl that would try to make set inode flags
> effective by evicting the inode (and returning EBUSY if the eviction is
> impossible for some reason)?

I'd just return an error for that case, don't play silly games like
evicting the inode.