Re: [PATCH bpf] tools/bpftool: fix PID fetching with a lot of results

[Yonghong Song <yhs@fb.com>]

On 12/4/20 3:20 PM, Andrii Nakryiko wrote:
> In case of having so many PID results that they don't fit into a singe page
> (4096) bytes, bpftool will erroneously conclude that it got corrupted data due
> to 4096 not being a multiple of struct pid_iter_entry, so the last entry will
> be partially truncated. Fix this by sizing the buffer to fit exactly N entries
> with no truncation in the middle of record.
> 
> Fixes: d53dee3fe013 ("tools/bpftool: Show info for processes holding BPF map/prog/link/btf FDs")
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Ack with one nit below.

Acked-by: Yonghong Song <yhs@fb.com>

> ---
>   tools/bpf/bpftool/pids.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/pids.c b/tools/bpf/bpftool/pids.c
> index df7d8ec76036..477e55d59c34 100644
> --- a/tools/bpf/bpftool/pids.c
> +++ b/tools/bpf/bpftool/pids.c
> @@ -89,9 +89,9 @@ libbpf_print_none(__maybe_unused enum libbpf_print_level level,
>   
>   int build_obj_refs_table(struct obj_refs_table *table, enum bpf_obj_type type)
>   {
> -	char buf[4096];
> -	struct pid_iter_bpf *skel;
>   	struct pid_iter_entry *e;
> +	char buf[4096 / sizeof(*e) * sizeof(*e)];
> +	struct pid_iter_bpf *skel;

No need to move "struct pid_iter_bpf *skel", right?

>   	int err, ret, fd = -1, i;
>   	libbpf_print_fn_t default_print;
>   
>