linux-kernel - Re: [PATCH bpf-next v4 5/5] selftests/bpf: Add test for open coded dmabuf

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Message-ID: <CABdmKX3LMJLTZN8-x8jFAM8p58pg-6P5-B=mHBf98_uAVtxxwQ@mail.gmail.com>
Date: Fri, 9 May 2025 15:27:54 -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 5/5] selftests/bpf: Add test for open coded dmabuf_iter

On Fri, May 9, 2025 at 2:58 PM Song Liu <song@...nel.org> wrote:
>
> On Fri, May 9, 2025 at 2:43 PM T.J. Mercier <tjmercier@...gle.com> wrote:
> >
> [...]
> > >
> > > Personally, I would prefer we just merge all the logic of
> > > create_udmabuf() and create_sys_heap_dmabuf()
> > > into create_test_buffers().
> >
> > That's a lot of different stuff to put in one place. How about
> > returning file descriptors from the buffer create functions while
> > having them clean up after themselves:
>
> I do like this version better. Some nitpicks though.
>
> >
> > -static int memfd, udmabuf;
> > +static int udmabuf;
>
> About this, and ...
>
> >  static const char udmabuf_test_buffer_name[DMA_BUF_NAME_LEN] =
> > "udmabuf_test_buffer_for_iter";
> >  static size_t udmabuf_test_buffer_size;
> >  static int sysheap_dmabuf;
> >  static const char sysheap_test_buffer_name[DMA_BUF_NAME_LEN] =
> > "sysheap_test_buffer_for_iter";
> >  static size_t sysheap_test_buffer_size;
> >
> > -static int create_udmabuf(int map_fd)
> > +static int create_udmabuf(void)
> >  {
> >         struct udmabuf_create create;
> > -       int dev_udmabuf;
> > -       bool f = false;
> > +       int dev_udmabuf, memfd, udmabuf;
> .. here.
>
> It is not ideal to have a global udmabuf and a local udmabuf.
> If we want the global version, let's rename the local one.

Ok let me change up the name of the aliasing variable to local_udmabuf.

> [...]
>
> >
> >  static int create_test_buffers(int map_fd)
> >  {
> > -       int ret;
> > +       bool f = false;
> > +
> > +       udmabuf = create_udmabuf();
> > +       sysheap_dmabuf = create_sys_heap_dmabuf();
> >
> > -       ret = create_udmabuf(map_fd);
> > -       if (ret)
> > -               return ret;
> > +       if (udmabuf < 0 || sysheap_dmabuf < 0)
> > +               return -1;
>
> We also need destroy_test_buffers() on the error path here,
> or at the caller.

The caller does currently check to decide if it should bother running
the tests or not, and calls destroy_test_buffers() if not.

> > -       return create_sys_heap_dmabuf(map_fd);
> > +       return bpf_map_update_elem(map_fd, udmabuf_test_buffer_name,
> > &f, BPF_ANY) ||
> > +              bpf_map_update_elem(map_fd, sysheap_test_buffer_name,
> > &f, BPF_ANY);
> >  }
> >
> >  static void destroy_test_buffers(void)
> >  {
> >         close(udmabuf);
> > -       close(memfd);
> >         close(sysheap_dmabuf);
>
> For the two global fds, let's reset them to -1 right after close().
>
> Thanks,
> Song

Will do, thanks.