Re: [PATCH v6 1/2] fuse: add FUSE_OPEN_ATOMIC

[Jimmy Zuber <jamz@amazon.com>]

On Fri, 30 Oct 2026, NeilBrown wrote:
> > - any other file: the server returns the entry only, and the VFS opens
> >   it;
>
> Why is this a requirement?  I understand that the server *may* choose to
> not open the file, so that the open doesn't happen until after the
> permission check.  But shouldn't be up to the server to decide.

This doesn't have to be a requirement, for regular files the server can
open if it chooses to. I'll reword. Are you also asking why this is just
regular files and not directories too? I could look into that if you'd
like? For what it's worth, special files should never get opened by the
server on this path, the kernel opens them itself.

> > The VFS checks the open after the reply, as for other ->atomic_open()
> > filesystems, and the kernel releases the file if the check fails.
> > FMODE_CREATED is set only when the server reports FOPEN_CREATED.
>
> The above para seems to suggest that the server might open a file that
> wasn't created.

Yeah, atomic_open is a lookup+open on the FUSE server, and that open
might be an open-create or just an open. Either way, the server might
open a preexisting file. I'll try to make all of this clearer in the
next rev, once I've gotten any feedback on directional changes here.

Thanks,
Jimmy