linux-kernel - Re: [PATCH v2 8/9] eventfs: moving tracing/events to eventfs

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Date:   Tue, 9 May 2023 12:29:23 +0000
From:   Ajay Kaher <akaher@...are.com>
To:     kernel test robot <lkp@...el.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "mhiramat@...nel.org" <mhiramat@...nel.org>,
        "shuah@...nel.org" <shuah@...nel.org>
CC:     "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        "oe-kbuild-all@...ts.linux.dev" <oe-kbuild-all@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-trace-kernel@...r.kernel.org" 
        <linux-trace-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "chinglinyu@...gle.com" <chinglinyu@...gle.com>,
        Nadav Amit <namit@...are.com>,
        Srivatsa Bhat <srivatsab@...are.com>,
        "srivatsa@...il.mit.edu" <srivatsa@...il.mit.edu>,
        Alexey Makhalov <amakhalov@...are.com>,
        Vasavi Sirnapalli <vsirnapalli@...are.com>,
        Tapas Kundu <tkundu@...are.com>,
        "er.ajay.kaher@...il.com" <er.ajay.kaher@...il.com>
Subject: Re: [PATCH v2 8/9] eventfs: moving tracing/events to eventfs


> On 02/05/23, 11:42 PM, "kernel test robot" <lkp@...el.com> wrote:
>   >> kernel/trace/trace_events.c:2424:17: warning: variable 'd_events' set but not used [-Wunused-but-set-variable]
>           struct dentry *d_events;
>                       ^
>    1 warning generated.
>

Steve, with-in event_create_dir(), do we have any scenario when file->event_call->class->system
doesn't have TRACE_SYSTEM? And need to execute following:

ae63b31e4d0e2e Steven Rostedt           2012-05-03  2437                d_events = parent;

looking for your input if we could remove d_events from event_create_dir().

- Ajay

>    vim +/d_events +2424 kernel/trace/trace_events.c
>
> ac343da7bc9048 Masami Hiramatsu         2020-09-10  2417
> 1473e4417c79f1 Steven Rostedt           2009-02-24  2418  static int
> 7f1d2f8210195c Steven Rostedt (Red Hat  2015-05-05  2419) event_create_dir(struct dentry *parent, struct trace_event_file *file)
> 1473e4417c79f1 Steven Rostedt           2009-02-24  2420  {
> 2425bcb9240f8c Steven Rostedt (Red Hat  2015-05-05  2421)       struct trace_event_call *call = file->event_call;
> ae63b31e4d0e2e Steven Rostedt           2012-05-03  2422        struct trace_array *tr = file->tr;
> 2fe2002efb23a7 Ajay Kaher               2023-05-02  2423        struct eventfs_file *ef_subsystem = NULL;
> ae63b31e4d0e2e Steven Rostedt           2012-05-03 @2424        struct dentry *d_events;
> de7b2973903c6c Mathieu Desnoyers        2014-04-08  2425        const char *name;
> fd99498989f3b3 Steven Rostedt           2009-02-28  2426        int ret;
> 1473e4417c79f1 Steven Rostedt           2009-02-24  2427
> 6ecc2d1ca39177 Steven Rostedt           2009-02-27  2428        /*
> 6ecc2d1ca39177 Steven Rostedt           2009-02-27  2429         * If the trace point header did not define TRACE_SYSTEM
> 6ecc2d1ca39177 Steven Rostedt           2009-02-27  2430         * then the system would be called "TRACE_SYSTEM".
> 6ecc2d1ca39177 Steven Rostedt           2009-02-27  2431         */
> ae63b31e4d0e2e Steven Rostedt           2012-05-03  2432        if (strcmp(call->class->system, TRACE_SYSTEM) != 0) {
> 2fe2002efb23a7 Ajay Kaher               2023-05-02  2433                ef_subsystem = event_subsystem_dir(tr, call->class->system, file, parent);
> 2fe2002efb23a7 Ajay Kaher               2023-05-02  2434                if (!ef_subsystem)
> ae63b31e4d0e2e Steven Rostedt           2012-05-03  2435                        return -ENOMEM;
> ae63b31e4d0e2e Steven Rostedt           2012-05-03  2436        } else
> ae63b31e4d0e2e Steven Rostedt           2012-05-03  2437                d_events = parent;
> 6ecc2d1ca39177 Steven Rostedt           2009-02-27  2438
> 687fcc4aee4567 Steven Rostedt (Red Hat  2015-05-13  2439)       name = trace_event_name(call);
> 2fe2002efb23a7 Ajay Kaher               2023-05-02  2440        file->ef = eventfs_add_dir(name, ef_subsystem, &tr->eventfs_rwsem);
> 2fe2002efb23a7 Ajay Kaher               2023-05-02  2441        if (IS_ERR(file->ef)) {
> 8434dc9340cd2e Steven Rostedt (Red Hat  2015-01-20  2442)               pr_warn("Could not create tracefs '%s' directory\n", name);
> 1473e4417c79f1 Steven Rostedt           2009-02-24  2443                return -1;
> 1473e4417c79f1 Steven Rostedt           2009-02-24  2444        }
> 1473e4417c79f1 Steven Rostedt           2009-02-24  2445
> 9b63776fa3ca96 Steven Rostedt           2012-05-10  2446        if (call->class->reg && !(call->flags & TRACE_EVENT_FL_IGNORE_ENABLE))
> 2fe2002efb23a7 Ajay Kaher               2023-05-02  2447                eventfs_add_file("enable", TRACE_MODE_WRITE, file->ef, file,
> 620a30e97febc8 Oleg Nesterov            2013-07-31  2448                                  &ftrace_enable_fops);
> 1473e4417c79f1 Steven Rostedt           2009-02-24  2449