linux-kernel - Re: [PATCH RESEND 1/3] tracing/syscalls: Rename variable 'nr' to 'syscall

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Date:	Thu, 25 Feb 2016 12:09:07 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Taeung Song <treeze.taeung@...il.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH RESEND 1/3] tracing/syscalls: Rename variable 'nr' to
 'syscall_nr'

On Thu, 25 Feb 2016 12:05:01 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Fri, 26 Feb 2016 01:53:47 +0900
> Taeung Song <treeze.taeung@...il.com> wrote:
> 
> > 
> > The underlying cause of this problem is not because of
> > the python script. This problem have relevance to tracing/syscalls
> > as below.
> > 
> > # cat 
> > /sys/kernel/debug/tracing/events/syscalls/sys_enter_io_getevents/format
> > name: sys_enter_io_getevents
> > ID: 739
> > format:
> >         field:unsigned short common_type; offset:0;size:2;signed:0;
> >         field:unsigned char common_flags; offset:2;size:1;signed:0;
> >         field:unsigned char common_preempt_count; offset:3;size:1;signed:0;
> >         field:int common_pid;             offset:4;size:4;signed:1;
> >         field:int nr;                     offset:8;size:4;signed:1;
> >         field:aio_context_t ctx_id;       offset:16;size:8;signed:0;
> >         field:long min_nr;                offset:24;size:8;signed:0;
> >         field:long nr;                    offset:32;size:8;signed:0;
> >         field:struct io_event * events;   offset:40;size:8;signed:0;
> >         field:struct timespec * timeout;  offset:48;size:8;signed:0;
> > 
> > print fmt: "ctx_id: 0x%08lx, min_nr: 0x%08lx, nr: 0x%08lx, events: 
> > 0x%08lx, timeout: 0x%08lx", ((unsigned long)(REC->ctx_id)), ((unsigned 
> > long)(REC->min_nr)), ((unsigned long)(REC->nr)), ((unsigned 
> > long)(REC->events)), ((unsigned long)(REC->timeout))
> > 
> > 
> > As you see, there are duplicated variable name among fields.
> > So I renamed the variable name 'nr' to 'syscall_nr' to avoid this
> > duplication. As you know 'nr' in print_syscall_enter() mean
> > system call number so, I changed 'nr' to 'syscall_nr'(IMHO).
> >   
> 
> The above should have been in the change log. That makes much more
> sense.
>

I'm a bit nervous about this change though. Because it is an ABI
change. Hopefully there's no tools that parse the syscall tracepoints
and expect to find a 'nr' in there.

-- Steve