netdev - Re: [PATCH v3 1/6] perf: prepare perf_event.h for new types perf_kprobe and perf

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Date:   Sun, 3 Dec 2017 09:03:14 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     peterz@...radead.org, rostedt@...dmis.org, mingo@...hat.com,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, daniel@...earbox.net,
        kernel-team@...com
Subject: Re: [PATCH v3 1/6] perf: prepare perf_event.h for new types
 perf_kprobe and perf_uprobe

On Thu, Nov 30, 2017 at 03:50:18PM -0800, Song Liu wrote:
> Two new perf types, perf_kprobe and perf_uprobe, will be added to allow
> creating [k,u]probe with perf_event_open. These [k,u]probe are associated
> with the file decriptor created by perf_event_open, thus are easy to
> clean when the file descriptor is destroyed.
> 
> kprobe_func and uprobe_path are added to union config1 for pointers to
> function name for kprobe or binary path for uprobe.
> 
> kprobe_addr and probe_offset are added to union config2 for kernel
> address (when kprobe_func is NULL), or [k,u]probe offset.
> 
> Signed-off-by: Song Liu <songliubraving@...com>
> Reviewed-by: Yonghong Song <yhs@...com>
> Reviewed-by: Josef Bacik <jbacik@...com>
> Acked-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  include/uapi/linux/perf_event.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 362493a..247c6cb 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -299,6 +299,8 @@ enum perf_event_read_format {
>  #define PERF_ATTR_SIZE_VER4	104	/* add: sample_regs_intr */
>  #define PERF_ATTR_SIZE_VER5	112	/* add: aux_watermark */
>  
> +#define MAX_PROBE_FUNC_NAME_LEN 64

I think we have to remove this restriction.
There are already functions with names longer than 64 characters
in the current vmlinux:
trace_event_define_fields_ext4_ext_convert_to_initialized_fastpath
trace_event_define_fields_mm_vmscan_direct_reclaim_begin_template

How about we drop this restriction and use NAME_MAX internally
without adding new uapi defines ?