From patchwork Thu Apr 18 21:24:05 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff King X-Patchwork-Id: 10908073 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E836B1515 for ; Thu, 18 Apr 2019 21:24:10 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C518828CBB for ; Thu, 18 Apr 2019 21:24:10 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B912D28CD0; Thu, 18 Apr 2019 21:24:10 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 5613B28CBB for ; Thu, 18 Apr 2019 21:24:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732180AbfDRVYH (ORCPT ); Thu, 18 Apr 2019 17:24:07 -0400 Received: from cloud.peff.net ([104.130.231.41]:34444 "HELO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1728264AbfDRVYH (ORCPT ); Thu, 18 Apr 2019 17:24:07 -0400 Received: (qmail 5777 invoked by uid 109); 18 Apr 2019 21:24:07 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.94) with SMTP; Thu, 18 Apr 2019 21:24:07 +0000 Authentication-Results: cloud.peff.net; auth=none Received: (qmail 4735 invoked by uid 111); 18 Apr 2019 21:24:38 -0000 Received: from sigill.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.7) by peff.net (qpsmtpd/0.94) with (ECDHE-RSA-AES256-GCM-SHA384 encrypted) SMTP; Thu, 18 Apr 2019 17:24:38 -0400 Authentication-Results: peff.net; auth=none Received: by sigill.intra.peff.net (sSMTP sendmail emulation); Thu, 18 Apr 2019 17:24:05 -0400 Date: Thu, 18 Apr 2019 17:24:05 -0400 From: Jeff King To: Junio C Hamano Cc: Johannes Schindelin via GitGitGadget , git@vger.kernel.org, Johannes Schindelin , =?utf-8?b?Tmd1eeG7hW4gVGjDoWkgTmfhu41j?= Duy Subject: [PATCH 4/3] untracked-cache: use FLEX_ALLOC to create internal structs Message-ID: <20190418212405.GA18623@sigill.intra.peff.net> References: <20190410162029.GA30818@sigill.intra.peff.net> <20190418211408.GA18011@sigill.intra.peff.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190418211408.GA18011@sigill.intra.peff.net> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On Thu, Apr 18, 2019 at 05:14:08PM -0400, Jeff King wrote: > Just so we don't forget about it, I wrote this fix up as a patch. And in > fact it led to a few other cleanups. I think the first one is definitely > worth doing now, even if there are other similar cases lurking in the > rest of the index code. > > The other two are optional, though I think they are worth it (and not > too hard to verify that they are doing the right thing). > > These are on top of js/untracked-cache-allocfix (though they could > easily be ported to a separate topic if we want). > > [1/3]: untracked-cache: be defensive about missing NULs in index > [2/3]: untracked-cache: simplify parsing by dropping "next" > [3/3]: untracked-cache: simplify parsing by dropping "len" I also wondered if we could just accept the cost of calloc() here and use FLEX_ALLOC to simplify things. That resulted in the patch below, but I didn't include it with the initial 3, because I think it's too subtle/gross for my tastes. -- >8 -- Subject: untracked-cache: use FLEX_ALLOC to create internal structs The untracked_cache_dir struct has a FLEX_ARRAY in it. Let's use FLEX_ALLOC_MEM to allocate it, which saves us having to compute the length ourselves. In theory this could be slightly slower, since the FLEX_ALLOC macros use calloc (and we just memcpy over most of the contents anyway). But in practice this distinction is not generally measurable. Note that because we then fill in the pre-flex elements of the struct using a memcpy, we need to take care to use the exact size of that space and _not_ "sizeof(ud)", since the latter may include padding (or even an extra byte on systems where FLEX_ARRAY is 1). Signed-off-by: Jeff King --- If we wanted to go this route, I think it would make sense to provide a FLEX_ALLOC macro that takes a "template" set of bytes as a ptr/len pair, and writes it before we fill in the flex portion. Then we could do something like: FLEX_ALLOC_COPY(untracked, &ud, sizeof(ud), name, data, eos - data); If this is the only such case, it's probably not worth it (I didn't really look around for more, though). dir.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/dir.c b/dir.c index 60438b2cdc..7cd4eec198 100644 --- a/dir.c +++ b/dir.c @@ -2757,9 +2757,9 @@ static int read_one_dir(struct untracked_cache_dir **untracked_, if (!eos || eos == end) return -1; - *untracked_ = untracked = xmalloc(st_add3(sizeof(*untracked), eos - data, 1)); - memcpy(untracked, &ud, sizeof(ud)); - memcpy(untracked->name, data, eos - data + 1); + FLEX_ALLOC_MEM(untracked, name, data, eos - data); + memcpy(untracked, &ud, offsetof(struct untracked_cache_dir, name)); + *untracked_ = untracked; data = eos + 1; for (i = 0; i < untracked->untracked_nr; i++) {