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Date:   Sun, 10 Jul 2022 17:30:20 -0700
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Subject: Re: [PATCH v5 bpf-next 2/2] selftests/bpf: add a ksym iter subtest
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To:     Alan Maguire <alan.maguire@oracle.com>, ast@kernel.org,
        andrii@kernel.org, daniel@iogearbox.net
Cc:     kafai@fb.com, songliubraving@fb.com, haoluo@google.com,
        john.fastabend@gmail.com, kpsingh@kernel.org, jolsa@kernel.org,
        mhiramat@kernel.org, akpm@linux-foundation.org, void@manifault.com,
        swboyd@chromium.org, ndesaulniers@google.com,
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        kuniyu@amazon.co.jp, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1657490998-31468-1-git-send-email-alan.maguire@oracle.com>
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From:   Yonghong Song <yhs@fb.com>
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On 7/10/22 3:09 PM, Alan Maguire wrote:
> add subtest verifying BPF ksym iter behaviour.  The BPF ksym
> iter program shows an example of dumping a format different to
> /proc/kallsyms.  It adds KIND and MAX_SIZE fields which represent the
> kind of symbol (core kernel, module, ftrace, bpf, or kprobe) and
> the maximum size the symbol can be.  The latter is calculated from
> the difference between current symbol value and the next symbol
> value.
> 
> The key benefit for this iterator will likely be supporting in-kernel
> data-gathering rather than dumping symbol details to userspace and
> parsing the results.
> 
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> Acked-by: Yonghong Song <yhs@fb.com>
> ---
>   tools/testing/selftests/bpf/prog_tests/bpf_iter.c | 16 +++++
>   tools/testing/selftests/bpf/progs/bpf_iter.h      | 32 ++++++++++
>   tools/testing/selftests/bpf/progs/bpf_iter_ksym.c | 74 +++++++++++++++++++++++
>   3 files changed, 122 insertions(+)
>   create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_ksym.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> index 7ff5fa9..a33874b 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> @@ -27,6 +27,7 @@
>   #include "bpf_iter_test_kern5.skel.h"
>   #include "bpf_iter_test_kern6.skel.h"
>   #include "bpf_iter_bpf_link.skel.h"
> +#include "bpf_iter_ksym.skel.h"
>   
>   static int duration;
>   
> @@ -1120,6 +1121,19 @@ static void test_link_iter(void)
>   	bpf_iter_bpf_link__destroy(skel);
>   }
>   
> +static void test_ksym_iter(void)
> +{
> +	struct bpf_iter_ksym *skel;
> +
> +	skel = bpf_iter_ksym__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "bpf_iter_ksym__open_and_load"))
> +		return;
> +
> +	do_dummy_read(skel->progs.dump_ksym);
> +
> +	bpf_iter_ksym__destroy(skel);
> +}
> +
>   #define CMP_BUFFER_SIZE 1024
>   static char task_vma_output[CMP_BUFFER_SIZE];
>   static char proc_maps_output[CMP_BUFFER_SIZE];
> @@ -1267,4 +1281,6 @@ void test_bpf_iter(void)
>   		test_buf_neg_offset();
>   	if (test__start_subtest("link-iter"))
>   		test_link_iter();
> +	if (test__start_subtest("ksym"))
> +		test_ksym_iter();
>   }
> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter.h b/tools/testing/selftests/bpf/progs/bpf_iter.h
> index 97ec8bc..4b23a08 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_iter.h
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter.h
> @@ -22,6 +22,8 @@
>   #define BTF_F_NONAME BTF_F_NONAME___not_used
>   #define BTF_F_PTR_RAW BTF_F_PTR_RAW___not_used
>   #define BTF_F_ZERO BTF_F_ZERO___not_used
> +#define bpf_iter__ksym bpf_iter__ksym___not_used
> +#define kallsym_iter kallsym_iter___not_used

There is no need to do kallsym_iter. This structure
should appear in vmlinux.h for all supporting bpf kernels.

>   #include "vmlinux.h"
>   #undef bpf_iter_meta
>   #undef bpf_iter__bpf_map
> @@ -44,6 +46,8 @@
>   #undef BTF_F_NONAME
>   #undef BTF_F_PTR_RAW
>   #undef BTF_F_ZERO
> +#undef bpf_iter__ksym
> +#undef kallsym_iter
>   
>   struct bpf_iter_meta {
>   	struct seq_file *seq;
> @@ -151,3 +155,31 @@ enum {
>   	BTF_F_PTR_RAW	=	(1ULL << 2),
>   	BTF_F_ZERO	=	(1ULL << 3),
>   };
> +
> +#ifndef KSYM_NAME_LEN
> +#define KSYM_NAME_LEN 128
> +#endif
> +
> +#ifndef MODULE_NAME_LEN
> +#define MODULE_NAME_LEN (64 - sizeof(unsigned long))
> +#endif
> +
> +struct kallsym_iter {
> +	loff_t pos;
> +	loff_t pos_arch_end;
> +	loff_t pos_mod_end;
> +	loff_t pos_ftrace_mod_end;
> +	loff_t pos_bpf_end;
> +	unsigned long value;
> +	unsigned int nameoff; /* If iterating in core kernel symbols. */
> +	char type;
> +	char name[KSYM_NAME_LEN];
> +	char module_name[MODULE_NAME_LEN];
> +	int exported;
> +	int show_value;
> +};
> +
> +struct bpf_iter__ksym {
> +	struct bpf_iter_meta *meta;
> +	struct kallsym_iter *ksym;
> +};
[...]