From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS3215 2.6.0.0/16 X-Spam-Status: No, score=-3.9 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from out1.vger.email (out1.vger.email [IPv6:2620:137:e000::1:20]) by dcvr.yhbt.net (Postfix) with ESMTP id 6A51F1F910 for ; Mon, 28 Nov 2022 05:16:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229602AbiK1FN4 (ORCPT ); Mon, 28 Nov 2022 00:13:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42130 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229586AbiK1FNz (ORCPT ); Mon, 28 Nov 2022 00:13:55 -0500 Received: from cloud.peff.net (cloud.peff.net [104.130.231.41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 59A1FF00C for ; Sun, 27 Nov 2022 21:13:54 -0800 (PST) Received: (qmail 7040 invoked by uid 109); 28 Nov 2022 05:13:54 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.94) with ESMTP; Mon, 28 Nov 2022 05:13:54 +0000 Authentication-Results: cloud.peff.net; auth=none Received: (qmail 339 invoked by uid 111); 28 Nov 2022 05:13:54 -0000 Received: from coredump.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.2) by peff.net (qpsmtpd/0.94) with (TLS_AES_256_GCM_SHA384 encrypted) ESMTPS; Mon, 28 Nov 2022 00:13:54 -0500 Authentication-Results: peff.net; auth=none Date: Mon, 28 Nov 2022 00:13:52 -0500 From: Jeff King To: Junio C Hamano Cc: Jiang Xin , Taylor Blau , Git List , Kyle Zhao , Jiang Xin Subject: Re: [PATCH] t5516: fail to run in verbose mode Message-ID: References: <20221121134040.12260-1-worldhello.net@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Fri, Nov 25, 2022 at 01:58:55PM +0900, Junio C Hamano wrote: > Jeff King writes: > > > One thing I'd worry about is buffering. One of the nice things about > > "-v" is that there is nothing between you and the running programs, so > > you are much less likely to be fooled about the order of events in the > > output. Or wondering why nothing is happening because real-time output > > seems to have stalled. But piping through "cat" may end up with weird > > pauses while it fills up a 4k buffer. Using stdbuf could help, but > > that's far from portable. > > We could pipe to "dd bs=1 conv=fsync" (tongue-in-cheek---I think > conv=fsync is a GNU thing). We don't need the fsync; we are just worried about in-process buffering, not kernel-level flushing. So bs=1 is sufficient, in that it would use syscalls to read/write single bytes. It would just be horribly inefficient. We really just want immediate partial read()/write() but with sensible buffer sizes. It would be easy to write a 5-line C program that did this if we really wanted to. I'm not entirely convinced it's worth worrying too much about, though. -Peff