netdev - Re: [PATCH 2/2] libbpf: Support repeated legacy kprobes on same function

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Date:   Mon, 27 Dec 2021 19:39:53 +0800
From:   Hengqi Chen <hengqi.chen@...il.com>
To:     Qiang Wang <wangqiang.wq.frank@...edance.com>, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, kafai@...com,
        songliubraving@...com, yhs@...com, john.fastabend@...il.com,
        kpsingh@...nel.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, zhouchengming@...edance.com,
        songmuchun@...edance.com, duanxiongchun@...edance.com,
        shekairui@...edance.com
Subject: Re: [PATCH 2/2] libbpf: Support repeated legacy kprobes on same
 function



On 2021/12/25 4:32 PM, Qiang Wang wrote:
> If repeated legacy kprobes on same function in one process,
> libbpf will register using the same probe name and got -EBUSY
> error. So append index to the probe name format to fix this
> problem.
> 
> Co-developed-by: Chengming Zhou <zhouchengming@...edance.com>
> Signed-off-by: Qiang Wang <wangqiang.wq.frank@...edance.com>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
>  tools/lib/bpf/libbpf.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index b7d6c951fa09..0c41a45ffd54 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9634,7 +9634,9 @@ static int append_to_file(const char *file, const char *fmt, ...)
>  static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
>  					 const char *kfunc_name, size_t offset)
>  {
> -	snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx", getpid(), kfunc_name, offset);
> +	static int index = 0;

Add empty line after variable declaration.

> +	snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx_%d", getpid(), kfunc_name, offset

Missing a comma after offset.

> +		 __sync_fetch_and_add(&index, 1));
>  }
>  
>  static int add_kprobe_event_legacy(const char *probe_name, bool retprobe,