linux-kernel - Re: [PATCH bpf-next 3/4] bpf: Introduce path iterator

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Message-ID: <20250602-lustig-erkennbar-7ef28fa97e20@brauner>
Date: Mon, 2 Jun 2025 11:27:43 +0200
From: Christian Brauner <brauner@...nel.org>
To: Song Liu <song@...nel.org>
Cc: Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
	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, kpsingh@...nel.org, 
	mattbobrowski@...gle.com, amir73il@...il.com, repnop@...gle.com, jlayton@...nel.org, 
	josef@...icpanda.com, mic@...ikod.net, gnoack@...gle.com
Subject: Re: [PATCH bpf-next 3/4] bpf: Introduce path iterator

On Thu, May 29, 2025 at 11:00:51AM -0700, Song Liu wrote:
> On Thu, May 29, 2025 at 10:38 AM Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > On Thu, May 29, 2025 at 09:53:21AM -0700, Song Liu wrote:
> >
> > > Current version of path iterator only supports walking towards the root,
> > > with helper path_parent. But the path iterator API can be extended
> > > to cover other use cases.
> >
> > Clarify the last part, please - call me paranoid, but that sounds like
> > a beginning of something that really should be discussed upfront.
> 
> We don't have any plan with future use cases yet. The only example
> I mentioned in the original version of the commit log is "walk the
> mount tree". IOW, it is similar to the current iterator, but skips non
> mount point iterations.
> 
> Since we call it "path iterator", it might make sense to add ways to
> iterate the VFS tree in different patterns. For example, we may

No, we're not adding a swiss-army knife for consumption by out-of-tree
code. I'm not opposed to adding a sane iterator for targeted use-cases
with a clear scope and internal API behavior as I've said multiple times
already on-list and in-person.

I will not merge anything that will endup exploding into some fancy
"walk subtrees in any order you want".