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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2EF85C433EF for ; Fri, 27 May 2022 10:29:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233479AbiE0K3v (ORCPT ); Fri, 27 May 2022 06:29:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350988AbiE0K32 (ORCPT ); Fri, 27 May 2022 06:29:28 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3AE7A12AB05; Fri, 27 May 2022 03:29:26 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id ED529219AC; Fri, 27 May 2022 10:29:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1653647364; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=m2R9qKdleRs8gByDqtRpf7rFuQ5Wqruhmv5hcFSY20I=; b=i+fAIbnglItVLQVZF1/abDNZofHSJPC/FCa/AJX1OKuhIRYYSbcw5kYdtT/ZwfZbX0pjqL bD+b3ewbBCzX9zGC/BPLGnB97SjvytIilWbs/Z4Dt7aYVU+EJmbjerXfNBpNm6mMHy0QRq KoRTVJSamMXUnOdB+FbSClHdFdVE/Z8= Received: from suse.cz (unknown [10.100.208.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 6F66F2C146; Fri, 27 May 2022 10:29:24 +0000 (UTC) Date: Fri, 27 May 2022 12:29:20 +0200 From: Petr Mladek To: Kent Overstreet Cc: linux-kernel@vger.kernel.org, linux-mm@vger.kernel.org, rostedt@goodmis.org, senozhatsky@chromium.org, andriy.shevchenko@linux.intel.com, willy@infradead.org Subject: Re: [PATCH v2 01/28] lib/printbuf: New data structure for printing strings Message-ID: References: <20220519172421.162394-1-kent.overstreet@gmail.com> <20220519172421.162394-2-kent.overstreet@gmail.com> <20220526152127.gw7gb4jnoikop4hl@moria.home.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220526152127.gw7gb4jnoikop4hl@moria.home.lan> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2022-05-26 11:21:27, Kent Overstreet wrote: > On Thu, May 26, 2022 at 05:06:15PM +0200, Petr Mladek wrote: > > On Thu 2022-05-19 13:23:54, Kent Overstreet wrote: > > > This adds printbufs: a printbuf points to a char * buffer and knows the > > > size of the output buffer as well as the current output position. > > > > > > Future patches will be adding more features to printbuf, but initially > > > printbufs are targeted at refactoring and improving our existing code in > > > lib/vsprintf.c - so this initial printbuf patch has the features > > > required for that. > > > > > diff --git a/include/linux/printbuf.h b/include/linux/printbuf.h > > > new file mode 100644 > > > index 0000000000..40dc07040d > > > --- /dev/null > > > +++ b/include/linux/printbuf.h > > > +static inline void pr_chars(struct printbuf *out, char c, unsigned n) > > > +{ > > > + memset(out->buf + out->pos, > > > + c, > > > + min(n, printbuf_remaining(out))); > > > + out->pos += n; > > > + printbuf_nul_terminate(out); > > > +} > > > > This function is not later used. Please, do not add API > > that will not have users in the same patchset. > > > > There are several other cases. I am not going to comment > > all of them. > > It is used in this patchset, in lib/vsnprintf.c. You sure about the other cases? Ah, I used outdated cscope. This was bad example. > > > +static inline void __pr_char(struct printbuf *out, char c) > > > +{ > > > + if (printbuf_remaining(out)) > > > + out->buf[out->pos] = c; > > > + out->pos++; > > > +} > > > + > > > +static inline void pr_char(struct printbuf *out, char c) > > > +{ > > > + __pr_char(out, c); > > > + printbuf_nul_terminate(out); > > > +} > > > > The "pr_" prefix is a nightmare for me because the same prefix > > is used also for printk() API ;-) > > > > Could we please use "pb_" instead? > > I'm not entirely against that, but I see printbufs as already in this patchset > tightly coupled to vsprintf.c and thus quite related to printk, as well - and > there aren't that many different pr_ things. So I think the shared prefix makes > some sense, I'd like to hear what others think before making that change. I would really like to keep the three APIs separated and easy to distinguish. They are principally different: 1. pr_*() API: + wrapper to printk(). They makes the messages available on console and for user-space log daemons while printf() + the various pr_*() variants are used to define kernel specific features and behavior, for example: loglevel, ratelimit, only once. deferred console handling. + uses implicit (system) buffer + The message format is defined by the 1st parameter. It is the same way as printf() in user-space. + It is inspired by printf() from user-space that prints the messages to the standard output. 2. *s*printf() APIs: + basically duplicate the same user-space API. It supports some extra %p modifiers. There might be few more incompatibilities. + use simple "char *" buffer provided as the 1st parameter + the messages format is defined the same way as in the user-space counterparts. 3. printbuf API: + append messages into the given printbuf by small pieces + format defined by the suffix, for example, _char(), bytes(), units_64(), _tab(), indent() + allows to do special operations on the buffer, for example, _reset(), make_room(), atomic_inc() + it will be used as low-level API for vscnprinf() implementation, pretty printing API, or stand alone uses. + I wonder if there will be variant that will allow to pass the format in the printf() way, e.g. int pb_printf(printbuf *buf, const char *fmt, ...); + is there any user space counter part? Now, it is clear that printfbuf API must be distinguished by another prefix: + it must be clear that it stores the output into printbuf. It is similar to dprintf(), fprintf(), sprintf(). + It can't be done by the suffix because it is already used to define format of the appended string or extra operation. + It must be clear what is low-level API used to implement vsprintf() and high-level API that uses vsprintf(). I mean pb_char() vs. pb_printf(). Best Regards, Petr PS: I probably won't find time to write more comments on this patchset today. I'll continue the following week. It seems that it will be a long journey.