linux-kernel - Re: [PATCH v5 bpf-next 1/5] namei: Introduce new helper function path_walk

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Message-ID: <CAPhsuW5GKn=0HWDKkmOMTge_rCEJ+UMRNnmo7HpT-gwtURHpiw@mail.gmail.com>
Date: Tue, 24 Jun 2025 10:37:36 -0700
From: Song Liu <song@...nel.org>
To: Jan Kara <jack@...e.cz>
Cc: bpf@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org, 
	kernel-team@...a.com, andrii@...nel.org, eddyz87@...il.com, ast@...nel.org, 
	daniel@...earbox.net, martin.lau@...ux.dev, viro@...iv.linux.org.uk, 
	brauner@...nel.org, kpsingh@...nel.org, mattbobrowski@...gle.com, 
	m@...wtm.org, neil@...wn.name
Subject: Re: [PATCH v5 bpf-next 1/5] namei: Introduce new helper function path_walk_parent()

Hi Jan,

On Tue, Jun 24, 2025 at 5:18 AM Jan Kara <jack@...e.cz> wrote:
>
> On Mon 16-06-25 23:11:12, Song Liu wrote:
> > This helper walks an input path to its parent. Logic are added to handle
> > walking across mount tree.
> >
> > This will be used by landlock, and BPF LSM.
> >
> > Suggested-by: Neil Brown <neil@...wn.name>
> > Signed-off-by: Song Liu <song@...nel.org>
>
> Looks good to me. Feel free to add:
>
> Reviewed-by: Jan Kara <jack@...e.cz>

Thanks for the review!

[...]

> > + *
> > + * Returns: either an ERR_PTR() or the chosen parent which will have had
> > + * the refcount incremented.
> > + */
>
> The behavior with LOOKUP_NO_XDEV is kind of odd (not your fault) and
> interestingly I wasn't able to find a place that would depend on the path
> being updated in that case. So either I'm missing some subtle detail (quite
> possible) or we can clean that up in the future.

We have RESOLVE_NO_XDEV in uapi/linux/openat2.h, so I guess we
cannot really remove it?

Thanks,
Song

[...]