netdev - Re: [PATCH v6 bpf-next 07/11] tracepoint: introduce kernel_tracepoint_find_by

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Date:   Tue, 27 Mar 2018 10:18:24 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     rostedt <rostedt@...dmis.org>
Cc:     Alexei Starovoitov <ast@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        netdev <netdev@...r.kernel.org>,
        kernel-team <kernel-team@...com>,
        linux-api <linux-api@...r.kernel.org>
Subject: Re: [PATCH v6 bpf-next 07/11] tracepoint: introduce
 kernel_tracepoint_find_by_name

----- On Mar 27, 2018, at 10:07 AM, rostedt rostedt@...dmis.org wrote:

> On Mon, 26 Mar 2018 19:47:02 -0700
> Alexei Starovoitov <ast@...com> wrote:
> 
>> From: Alexei Starovoitov <ast@...nel.org>
>> 
>> introduce kernel_tracepoint_find_by_name() helper to let bpf core
>> find tracepoint by name and later attach bpf probe to a tracepoint
>> 
>> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> 
> Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Steven showed preference for tracepoint_kernel_find_by_name() at some
point (starting with a tracepoint_ prefix). I'm find with either of
the names.

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Thanks,

Mathieu

> 
> Thanks for doing this Alexei!
> 
> One nit below.
> 
> 
>> ---
>>  include/linux/tracepoint.h | 6 ++++++
>>  kernel/tracepoint.c        | 9 +++++++++
>>  2 files changed, 15 insertions(+)
>> 
>> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
>> index c92f4adbc0d7..a00b84473211 100644
>> --- a/include/linux/tracepoint.h
>> +++ b/include/linux/tracepoint.h
>> @@ -43,6 +43,12 @@ tracepoint_probe_unregister(struct tracepoint *tp, void
>> *probe, void *data);
>>  extern void
>>  for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
>>  		void *priv);
>> +#ifdef CONFIG_TRACEPOINTS
>> +struct tracepoint *kernel_tracepoint_find_by_name(const char *name);
>> +#else
>> +static inline struct tracepoint *
>> +kernel_tracepoint_find_by_name(const char *name) { return NULL; }
>> +#endif
>>  
>>  #ifdef CONFIG_MODULES
>>  struct tp_module {
>> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
>> index 671b13457387..e2a9a0391ae2 100644
>> --- a/kernel/tracepoint.c
>> +++ b/kernel/tracepoint.c
>> @@ -528,6 +528,15 @@ void for_each_kernel_tracepoint(void (*fct)(struct
>> tracepoint *tp, void *priv),
>>  }
>>  EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);
>>  
>> +struct tracepoint *kernel_tracepoint_find_by_name(const char *name)
>> +{
>> +	struct tracepoint * const *tp = __start___tracepoints_ptrs;
>> +
>> +	for (; tp < __stop___tracepoints_ptrs; tp++)
>> +		if (!strcmp((*tp)->name, name))
>> +			return *tp;
> 
> 
> Usually for cases like this, we prefer to add brackets for the for
> block, as it's not a single line below it.
> 
>	for (; tp < __stop__tracepoints_ptrs; tp++) {
>		if (!strcmp((*tp)->name, name))
>			return *tp;
>	}
> 
> -- Steve
> 
> 
>	
> 
>> +	return NULL;
>> +}
>>  #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
>>  
> >  /* NB: reg/unreg are called while guarded with the tracepoints_mutex */

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com