Re: [PATCH v2 0/4] Stash overlay real upper file in backing_file

[Miklos Szeredi <miklos@szeredi.hu>]

On Mon, 7 Oct 2024 at 13:02, Amir Goldstein <amir73il@gmail.com> wrote:

> What I see after my patch is that ->private_data points to a singly
> linked list of length 1 to 2 of backing files.

Well, yeah.

Still, it's adding (arguably minimal) data and code to backing_file,
that is overlay specific.   If you show how this is relevant to fuse's
use of backing files, then that's a much stronger argument in favor.

> Well, this is not any worth that current ->private_data, but I could
> also make it, if you like it better:
>
>  struct backing_file {
>         struct file file;
>         struct path user_path;
> +       struct file *next;
>  };
>
> +struct file **backing_file_private_ptr(struct file *f)
> +{
> +       return &backing_file(f)->next;
> +}
> +EXPORT_SYMBOL_GPL(backing_file_next_ptr);

Yeah, that would solve type safety, but would make the infrastructure
less generic.

> Again, I am not terribly opposed to allocating struct ovl_file as we do
> with directory - it is certainly more straight forward to read, so that
> is a good enough argument in itself, and "personal dislike" is also a fair
> argument, just arguing for the sake of argument so you understand my POV.

I think readability is more important here than savings on memory or CPU.

Thanks,
Miklos