Re: [PATCH v3 09/14] vfs: add O_CREAT|O_DIRECTORY to open*(2)

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jul 22, 2026 at 02:51:54PM +0200, Christian Brauner wrote:
> > No, we can't rely on something being backport to old enterprise/cloud
> > kernel.  Doing so makes the interface unusable for actual applications.
> 
> It's backported to all LTS kernels for multiple years and this
> nonsensical theory of using a software version with O_DIRECTORY |
> O_CREAT on a pre-LTS kernel from years ago is just flimsy.

the kernel has always ignored unknown open flags, or unchecked
combinations and you can't just silently give them a meaning unless
it is backwars compatible.  That has nothing to do with this particular
combination.

> 
> Even just the mere fact that I was able to just backport that bugfix
> that started returning hard errors to all LTS kernels with absolutely
> zero regression reports defeats that argument. We've done way more
> invasive changes. This is a strawman really. 

Of course it didn't break anything yet because no one used it yet.
One we give it a meaning it will be used and break.  And if you like
it or not, a lot o Linux deployment is not using recent stable releases
or even tracking the -stable releases at all.

Just like we've always done in the past we'll need to APIs that don't
accidentally do the wrong thing on any old kernel.  We've survived doing
it this way the last 25 years (maybe longer, but that's about how long
I've been around) and there is no reason to magically change this now.