linux-kernel - Re: [PATCH] mm/filemap: add static for function __add_to_page_cache

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Message-ID: <CAADnVQKiBWG9NVNEV9EqGkyd-n3Yj88cNJpH997js-63eTVAOQ@mail.gmail.com>
Date:   Wed, 9 Dec 2020 17:12:43 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Stanislaw Gruszka <stf_xl@...pl>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Kubecek <mkubecek@...e.cz>,
        Justin Forbes <jmforbes@...uxtx.org>,
        bpf <bpf@...r.kernel.org>, Alex Shi <alex.shi@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Josef Bacik <josef@...icpanda.com>
Subject: Re: [PATCH] mm/filemap: add static for function __add_to_page_cache_locked

On Wed, Dec 9, 2020 at 2:32 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Wed, Dec 09, 2020 at 06:05:52PM +0000, Christoph Hellwig wrote:
> > On Wed, Dec 09, 2020 at 04:51:48PM +0100, Stanislaw Gruszka wrote:
> > > On Wed, Dec 09, 2020 at 03:08:26PM +0000, Matthew Wilcox wrote:
> > > > On Wed, Dec 09, 2020 at 03:46:28PM +0100, Stanislaw Gruszka wrote:
> > > > > At this point of release cycle we should probably go with revert,
> > > > > but I think the main problem is that BPF and ERROR_INJECTION use
> > > > > function that is not intended to be used externally. For external users
> > > > > add_to_page_cache_lru() and add_to_page_cache_locked() are exported
> > > > > and I think those should be used (see the patch below).
> > > >
> > > > FWIW, I intend to do some consolidation/renaming in this area.  I
> > > > trust that will not be a problem?
> > >
> > > If it does not break anything, it will be not a problem ;-)
> > >
> > > It's possible that __add_to_page_cache_locked() can be a global symbol
> > > with add_to_page_cache_lru() + add_to_page_cache_locked() being just
> > > static/inline wrappers around it.
> >
> > So what happens to BTF if we change this area entirely?  Your IDs
> > sound like some kind of ABI to me, which is extremely scary.
>
> Is BTF becoming the new tracepoint? That is, random additions of things like:
>
>    BTF_ID(func,__add_to_page_cache_locked)
>
> Like was done in commit 1e6c62a882155 ("bpf: Introduce sleepable BPF
> programs") without any notification to the maintainers of the
> __add_to_page_cache_locked code, will suddenly become an API?

huh? what api/abi you're talking about?