From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D9E30C433B4 for ; Mon, 5 Apr 2021 14:23:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 98A91613B2 for ; Mon, 5 Apr 2021 14:23:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237234AbhDEOXZ (ORCPT ); Mon, 5 Apr 2021 10:23:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:57950 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237153AbhDEOXY (ORCPT ); Mon, 5 Apr 2021 10:23:24 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6794A6139E; Mon, 5 Apr 2021 14:23:18 +0000 (UTC) Date: Mon, 5 Apr 2021 10:23:16 -0400 From: Steven Rostedt To: "Tzvetomir Stoyanov (VMware)" Cc: linux-trace-devel@vger.kernel.org Subject: Re: [PATCH] trace-cmd: Implement warning() in the library Message-ID: <20210405102316.5d28cc58@gandalf.local.home> In-Reply-To: <20210405095920.526d8922@gandalf.local.home> References: <20210405093357.870395-1-tz.stoyanov@gmail.com> <20210405095920.526d8922@gandalf.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org On Mon, 5 Apr 2021 09:59:20 -0400 Steven Rostedt wrote: > On Mon, 5 Apr 2021 12:33:57 +0300 > "Tzvetomir Stoyanov (VMware)" wrote: > > > The warning() function is used in a lot of places in the trace-cmd > > library, but there is no implementation. The function is implemented in > > the trace-cmd application. Added a weak implementation in the library, in > > case the function in not implemented in the application, using that > > library. > > > > Isn't the "warning()" function implemented in libtraceevent? That's where > it would be used as it is weak there. > > But honestly, I think we should change the libtraceveent warning to > "tep_warning()" if we haven't already done so. > > /me goes to look at the code. OK, so what I think we need to do is have this: void __weak tep_print_error(const char *fmt, const char *app, va_list ap) { if (errno) perror(app); fprintf(stderr, " "); vfprintf(stderr, fmt, ap); fprintf(stderr, "\n"); } That gets the format and a va_list, and this is the weak function that anything can overwrite (like KernelShark to have a pop up on error?). Then we can have functions: void __weak tep_vwarning(const char *fmt, va_list ap) { tep_print_error(fmt, "libtraceevent", ap); } void __weak tep_warning(const char *fmt, ...) { va_list ap; va_start(ap, fmt); tep_vwarning(fmt, ap); va_end(ap); } And the same for libtracefs and libtracecmd. where it will have a tracefs_warning() and a tracecmd_warning() functions defined. Then an app can overwrite how tep_print_error() works, as well as tep_vwarning works (or tracefs_vwarning() etc). Hmm, thinking about this, there's no reason to have tep_warning() weak, because by overwriting tep_vwarning(), you have full control of tep_warning(). -- Steve