linux-kernel - Re: [PATCH bpf-next v6 4/5] selftests/bpf: Add test for dmabuf

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Message-ID: <CABdmKX3Q5+bfbBBndSS6mxUhapFGY5zLr9CV-p0+CfNPOzuvGA@mail.gmail.com>
Date: Wed, 14 May 2025 14:58:57 -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 v6 4/5] selftests/bpf: Add test for dmabuf_iter

On Wed, May 14, 2025 at 1:53 PM Song Liu <song@...nel.org> wrote:
>
> On Tue, May 13, 2025 at 9:36 AM T.J. Mercier <tjmercier@...gle.com> wrote:
> >
> > This test creates a udmabuf, and a dmabuf from the system dmabuf heap,
> > and uses a BPF program that prints dmabuf metadata with the new
> > dmabuf_iter to verify they can be found.
> >
> > Signed-off-by: T.J. Mercier <tjmercier@...gle.com>
> > Acked-by: Christian König <christian.koenig@....com>
>
> Acked-by: Song Liu <song@...nel.org>

Thanks.

>
> With one more comment below.
>
> [...]
>
> > diff --git a/tools/testing/selftests/bpf/progs/dmabuf_iter.c b/tools/testing/selftests/bpf/progs/dmabuf_iter.c
> > new file mode 100644
> > index 000000000000..2a1b5397196d
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/dmabuf_iter.c
> > @@ -0,0 +1,53 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (c) 2025 Google LLC */
> > +#include <vmlinux.h>
> > +#include <bpf/bpf_core_read.h>
> > +#include <bpf/bpf_helpers.h>
> > +
> > +/* From uapi/linux/dma-buf.h */
> > +#define DMA_BUF_NAME_LEN 32
> > +
> > +char _license[] SEC("license") = "GPL";
> > +
> > +/*
> > + * Fields output by this iterator are delimited by newlines. Convert any
> > + * newlines in user-provided printed strings to spaces.
> > + */
> > +static void sanitize_string(char *src, size_t size)
> > +{
> > +       for (char *c = src; *c && (size_t)(c - src) < size; ++c)
>
> We should do the size check first, right? IOW:
>
> for (char *c = src; (size_t)(c - src) < size && *c; ++c)

Yeah if you call the function with size = 0, which is kinda
questionable and not possible with the non-zero array size that is
tied to immutable UAPI. Let's change it like you suggest.


>
> > +               if (*c == '\n')
> > +                       *c = ' ';
> > +}
> > +
> [...]