linux-kernel - Re: [PATCH 4/4] nfs: sysfs: use default get

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Message-ID: <CAK-6q+h4rsitB5C-dh=gpF5wG_1P2M=qT0wSVhTjLjkHLEsXsg@mail.gmail.com>
Date: Wed, 9 Oct 2024 10:56:15 -0400
From: Alexander Aring <aahringo@...hat.com>
To: Benjamin Coddington <bcodding@...hat.com>
Cc: trondmy@...nel.org, anna@...nel.org, gregkh@...uxfoundation.org, 
	rafael@...nel.org, akpm@...ux-foundation.org, linux-nfs@...r.kernel.org, 
	gfs2@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] nfs: sysfs: use default get_ownership() callback

Hi,

On Tue, Oct 8, 2024 at 4:09 PM Benjamin Coddington <bcodding@...hat.com> wrote:
>
> On 3 Oct 2024, at 11:14, Alexander Aring wrote:
>
> > Since commit 5f81880d5204 ("sysfs, kobject: allow creating kobject
> > belonging to arbitrary users") it seems that there could be cases for
> > kobjects belonging to arbitrary users. This callback is set by default
> > when using kset_create_and_add() to allow creating kobjects with
> > different ownerships according to its parent.
> >
> > This patch will assign the default callback now for nfs kobjects for
> > cases when the parent has different ownership than the default one.
> >
> > Signed-off-by: Alexander Aring <aahringo@...hat.com>
> > ---
> >  fs/nfs/sysfs.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/fs/nfs/sysfs.c b/fs/nfs/sysfs.c
> > index a6584203b7ff..b5737464b892 100644
> > --- a/fs/nfs/sysfs.c
> > +++ b/fs/nfs/sysfs.c
> > @@ -27,6 +27,7 @@ static const struct kobj_ns_type_operations *nfs_netns_object_child_ns_type(
> >  }
> >
> >  static struct kobj_type nfs_kset_type = {
> > +     .get_ownership = kset_get_ownership,
> >       .release = kset_release,
> >       .sysfs_ops = &kobj_sysfs_ops,
> >       .child_ns_type = nfs_netns_object_child_ns_type,
> > --
> > 2.43.0
>
> Hi Alex, if I understand this correctly, this patch just punts the ownership
> callback up to fs_kobj, which, because it has no .get_ownership is just
> going to be the same result: root.
>

Yes, from my understanding this has to do with user namespaces and
being able to write to the related sysfs/kobject files?

> Does this patch add value?
>

For me no, but it is there now as default and I think somebody
probably forgot to update all the other users that created their kset
in a more low-level kind of way.
I think the whole "transitioning process" to make the same things with
namespaces created under root vs user is still kind of still in
process.

I am not sure if any of the nfs userspace namespace aware tools are
also limited by other things that require additional changes to do
something else as a "normal" user.

For me it's fine to drop this patch series and if somebody wants to
make a user namespace working with nfs tooling can come back again and
find out such patch might be necessary?

Thanks.

- Alex