linux-kernel - Re: [PATCH 09/17] file: Implement fnext

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Message-ID: <20200818110556.q5i5quflrcljv4wa@wittgenstein>
Date:   Tue, 18 Aug 2020 13:05:56 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "<linux-fsdevel@...r.kernel.org>" <linux-fsdevel@...r.kernel.org>,
        criu@...nvz.org, bpf <bpf@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Oleg Nesterov <oleg@...hat.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Jann Horn <jann@...jh.net>, Kees Cook <keescook@...omium.org>,
        Daniel P. Berrangé <berrange@...hat.com>,
        Jeff Layton <jlayton@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Matthew Wilcox <willy@...ian.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Matthew Wilcox <matthew@....cx>,
        Trond Myklebust <trond.myklebust@....uio.no>,
        Chris Wright <chrisw@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH 09/17] file: Implement fnext_task

On Mon, Aug 17, 2020 at 06:17:35PM -0700, Linus Torvalds wrote:
> On Mon, Aug 17, 2020 at 6:06 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
> >
> > I struggle with the fcheck name as I have not seen or at least not
> > registed on the the user that just checks to see if the result is NULL.
> > So the name fcheck never made a bit of sense to me.
> 
> Yeah, that name is not great. I just don't want to make things even worse.
> 
> > I will see if I can come up with some good descriptive comments around
> > these functions.  Along with describing what these things are doing I am
> > thinking maybe I should put "_rcu" in their names and have a debug check
> > that verifies "_rcu" is held.
> 
> Yeah, something along the lines of "rcu_lookup_fd_task(tsk,fd)" would
> be a *lot* more descriptive than fcheck_task().
> 
> And I think "fnext_task()" could be "rcu_lookup_next_fd_task(tsk,fd)".
> 
> Yes, those are much longer names, but it's not like you end up typing
> them all that often, and I think being descriptive would be worth it.
> 
> And "fcheck()" and "fcheck_files()" would be good to rename too along
> the same lines.
> 
> Something like "rcu_lookup_fd()" and "rcu_lookup_fd_files()" respectively?
> 
> I'm obviously trying to go for a "rcu_lookup_fd*()" kind of pattern,
> and I'm not married to _that_ particular pattern but I think it would
> be better than what we have now.

In fs/inode.c and a few other places we have the *_rcu suffix pattern
already so maybe:

fcheck() -> fd_file_rcu() or lookup_fd_rcu()
fcheck_files() -> fd_files_rcu() or lookup_fd_files_rcu()
fnext_task() -> fd_file_from_task_rcu() or lookup_next_fd_from_task_rcu()

rather than as prefix or sm.

Christian