linux-kernel - Re: [PATCH bpf-next v4 3/5] bpf: Add open coded dmabuf iterator

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Message-ID: <CABdmKX0t-ng2WJPUdjXUgtbyNks4vcp3rVNbQOGPNFRF5kTQGQ@mail.gmail.com>
Date: Fri, 9 May 2025 10:13:26 -0700
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Song Liu <song@...nel.org>
Cc: sumit.semwal@...aro.org, christian.koenig@....com, ast@...nel.org, 
	daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev, 
	skhan@...uxfoundation.org, alexei.starovoitov@...il.com, 
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org, 
	bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, android-mm@...gle.com, 
	simona@...ll.ch, eddyz87@...il.com, yonghong.song@...ux.dev, 
	john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me, 
	jolsa@...nel.org, mykolal@...com, shuah@...nel.org
Subject: Re: [PATCH bpf-next v4 3/5] bpf: Add open coded dmabuf iterator

On Thu, May 8, 2025 at 5:28 PM Song Liu <song@...nel.org> wrote:
>
> On Thu, May 8, 2025 at 11:20 AM T.J. Mercier <tjmercier@...gle.com> wrote:
> >
> > This open coded iterator allows for more flexibility when creating BPF
> > programs. It can support output in formats other than text. With an open
> > coded iterator, a single BPF program can traverse multiple kernel data
> > structures (now including dmabufs), allowing for more efficient analysis
> > of kernel data compared to multiple reads from procfs, sysfs, or
> > multiple traditional BPF iterator invocations.
> >
> > Signed-off-by: T.J. Mercier <tjmercier@...gle.com>
>
> Acked-by: Song Liu <song@...nel.org>
>
> With one nitpick below:
>
> > ---
> >  kernel/bpf/dmabuf_iter.c | 47 ++++++++++++++++++++++++++++++++++++++++
> >  kernel/bpf/helpers.c     |  5 +++++
> >  2 files changed, 52 insertions(+)
> >
> > diff --git a/kernel/bpf/dmabuf_iter.c b/kernel/bpf/dmabuf_iter.c
> > index 96b4ba7f0b2c..8049bdbc9efc 100644
> > --- a/kernel/bpf/dmabuf_iter.c
> > +++ b/kernel/bpf/dmabuf_iter.c
> > @@ -100,3 +100,50 @@ static int __init dmabuf_iter_init(void)
> >  }
> >
> >  late_initcall(dmabuf_iter_init);
> > +
> > +struct bpf_iter_dmabuf {
> > +       /* opaque iterator state; having __u64 here allows to preserve correct
> > +        * alignment requirements in vmlinux.h, generated from BTF
> > +        */
>
> nit: comment style.

Added a leading /*

(This is copied from task_iter.c, which currently has the same style.)


> > +       __u64 __opaque[1];
> > +} __aligned(8);
> > +
> > +/* Non-opaque version of bpf_iter_dmabuf */
> > +struct bpf_iter_dmabuf_kern {
> > +       struct dma_buf *dmabuf;
> > +} __aligned(8);
> > +
> [...]