linux-kernel - Re: [PATCH 03/11] tracing: add soft disable for syscall events

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Date:	Fri, 21 Jun 2013 14:53:26 +0800
From:	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>
To:	Tom Zanussi <tom.zanussi@...ux.intel.com>
CC:	<rostedt@...dmis.org>, <masami.hiramatsu.pt@...achi.com>,
	<linux-kernel@...r.kernel.org>, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 03/11] tracing: add soft disable for syscall events

On 2013/6/21 2:31, Tom Zanussi wrote:
> Add support for SOFT_DISABLE to syscall events.
> 
> The original SOFT_DISABLE patches didn't add support for soft disable
> of syscall events; this adds it and paves the way for future patches
> allowing triggers to be added to syscall events, since triggers are
> built on top of SOFT_DISABLE.
> 
> Because the trigger and SOFT_DISABLE bits are attached to the
> ftrace_event_file associated with the event, pointers to the
> ftrace_event_files associated with the event are added to the syscall
> metadata entry for the event.
> 
> Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> ---
>  include/linux/syscalls.h      |  2 ++
>  include/trace/syscall.h       |  5 +++++
>  kernel/trace/trace_syscalls.c | 28 ++++++++++++++++++++++++----
>  3 files changed, 31 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 4147d70..b4c2afa 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -158,6 +158,8 @@ extern struct trace_event_functions exit_syscall_print_funcs;
>  		.args		= nb ? args_##sname : NULL,	\
>  		.enter_event	= &event_enter_##sname,		\
>  		.exit_event	= &event_exit_##sname,		\
> +		.enter_file	= NULL,	/* Filled in at boot */	\
> +		.exit_file	= NULL,	/* Filled in at boot */	\
>  		.enter_fields	= LIST_HEAD_INIT(__syscall_meta_##sname.enter_fields), \
>  	};							\
>  	static struct syscall_metadata __used			\
> diff --git a/include/trace/syscall.h b/include/trace/syscall.h
> index fed853f..ba24d3a 100644
> --- a/include/trace/syscall.h
> +++ b/include/trace/syscall.h
> @@ -19,6 +19,8 @@
>   * @enter_fields: list of fields for syscall_enter trace event
>   * @enter_event: associated syscall_enter trace event
>   * @exit_event: associated syscall_exit trace event
> + * @enter_file: associated syscall_enter ftrace event file
> + * @exit_file: associated syscall_exit ftrace event file
>   */
>  struct syscall_metadata {
>  	const char	*name;
> @@ -30,6 +32,9 @@ struct syscall_metadata {
>  
>  	struct ftrace_event_call *enter_event;
>  	struct ftrace_event_call *exit_event;
> +
> +	struct ftrace_event_file *enter_file;
> +	struct ftrace_event_file *exit_file;
>  };

I doubt this could work correctly.
struct ftrace_event_file is allocated dynamically, there could
have many ftrace_event_file in there, associated with different trace_array,
it means there may have many ftrace_event_file linked with same syscall_metadata.

The enter_file/exit_file pointer of syscall_metadata will be override if another
ftrace_event_file registered in some other trace_array.

Perhaps we could use simple list_head in here, which link with all registered ftrace_event_file.

Oleg use "struct event_file_link" for trace_kprobe, the structure could be reuse in here.


struct event_file_link {
	struct ftrace_event_file	*file;
	struct list_head		list;
};

struct syscall_metadata {
        const char      *name;
        int             syscall_nr;
        int             nb_args;
        const char      **types;
        const char      **args;
        struct list_head enter_fields;

        struct ftrace_event_call *enter_event;
        struct ftrace_event_call *exit_event;

	struct list_head	enter_files;
	struct list_head	exit_files;
};


.jovi


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