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SubjectRe: [PATCH bpf-next v2] bpftool: Dump map id instead of value for map_of_maps types
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On 4/24/23 02:09, Xueming Feng wrote:
> When using `bpftool map dump` in plain format, it is usually
> more convenient to show the inner map id instead of raw value.
> Changing this behavior would help with quick debugging with
> `bpftool`, without disrupting scripted behavior. Since user
> could dump the inner map with id, and need to convert value.
>
> Signed-off-by: Xueming Feng <kuro@kuroa.me>
> ---
> Changes in v2:
> - Fix commit message grammar.
> - Change `print_uint` to only print to stdout, make `arg` const, and rename
> `n` to `arg_size`.
> - Make `print_uint` able to take any size of argument up to `unsigned long`,
> and print it as unsigned decimal.
>
> Thanks for the review and suggestions! I have changed my patch accordingly.
> There is a possibility that `arg_size` is larger than `unsigned long`,
> but previous review suggested that it should be up to the caller function to
> set `arg_size` correctly. So I didn't add check for that, should I?
>
> tools/bpf/bpftool/main.c | 15 +++++++++++++++
> tools/bpf/bpftool/main.h | 1 +
> tools/bpf/bpftool/map.c | 9 +++++++--
> 3 files changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
> index 08d0ac543c67..810c0dc10ecb 100644
> --- a/tools/bpf/bpftool/main.c
> +++ b/tools/bpf/bpftool/main.c
> @@ -251,6 +251,21 @@ int detect_common_prefix(const char *arg, ...)
> return 0;
> }
>
> +void print_uint(const void *arg, unsigned int arg_size)
> +{
> + const unsigned char *data = arg;
> + unsigned long val = 0ul;
> +
> + #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
> + memcpy(&val, data, arg_size);
> + #else
> + memcpy((unsigned char *)&val + sizeof(val) - arg_size,
> + data, arg_size);
> + #endif

Is it possible that arg_size is bigger than sizeof(val)?

> +
> + fprintf(stdout, "%lu", val);
> +}
> +
> void fprint_hex(FILE *f, void *arg, unsigned int n, const char *sep)
> {
> unsigned char *data = arg;
> diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
> index 0ef373cef4c7..0de671423431 100644
> --- a/tools/bpf/bpftool/main.h
> +++ b/tools/bpf/bpftool/main.h
> @@ -90,6 +90,7 @@ void __printf(1, 2) p_info(const char *fmt, ...);
>
> bool is_prefix(const char *pfx, const char *str);
> int detect_common_prefix(const char *arg, ...);
> +void print_uint(const void *arg, unsigned int arg_size);
> void fprint_hex(FILE *f, void *arg, unsigned int n, const char *sep);
> void usage(void) __noreturn;
>
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index aaeb8939e137..f5be4c0564cf 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -259,8 +259,13 @@ static void print_entry_plain(struct bpf_map_info *info, unsigned char *key,
> }
>
> if (info->value_size) {
> - printf("value:%c", break_names ? '\n' : ' ');
> - fprint_hex(stdout, value, info->value_size, " ");
> + if (map_is_map_of_maps(info->type)) {
> + printf("id:%c", break_names ? '\n' : ' ');
> + print_uint(value, info->value_size);
> + } else {
> + printf("value:%c", break_names ? '\n' : ' ');
> + fprint_hex(stdout, value, info->value_size, " ");
> + }
> }
>
> printf("\n");

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