From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.1 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 7DA4620960 for ; Tue, 11 Apr 2017 00:58:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752303AbdDKA6U (ORCPT ); Mon, 10 Apr 2017 20:58:20 -0400 Received: from mail-pf0-f173.google.com ([209.85.192.173]:36673 "EHLO mail-pf0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750761AbdDKA6T (ORCPT ); Mon, 10 Apr 2017 20:58:19 -0400 Received: by mail-pf0-f173.google.com with SMTP id o126so40836156pfb.3 for ; Mon, 10 Apr 2017 17:58:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=2GzxV7vJSXpm3S3GJkAdXqyXCT1FFKWWAik86/WQFEk=; b=mg0bHvsUwmv+vqAuxzmGN2Hgq2s7s6ok8rtqtWtMV9zbNhZSSOWaEsqOCKZlcBHmSt GTgC6Jtojd4HhDlKJ5zizehD4PwIGH7FhILlUkC05zdjCnw7boQ9GZ8gbgq/ElaC0/lz o7a+uwszyC0VZ/Ftrma61utmb0wdWZHtzF4E4fW5Q2hz6wBbUHUWVBYKwlWpJWAO0HoJ DEoXiTdf+P2s0e1YTwC5/qdMDRaaKksWjcby9LVAZBRk3CzcRb5lj5pCsr5LreeyQTrY 5XAD8YjU86VZDCEy+kp2tnLr2s6OeF2KYaJQWwLc46IuXOIP81dCxcKDY7i5t4jeO6hL uFcQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=2GzxV7vJSXpm3S3GJkAdXqyXCT1FFKWWAik86/WQFEk=; b=Skhq6MCraSvb2oxqB6Bikf02P6VBQVFO1gvE1+rTjlVUUl0OnI8K4wLeG7whkkqlEk l05UpFVmUvZ3cwO9a6f0qiWbqnvk2xB/Su9thn360rCBgwvGEWO9KzycPx5gOZMeFQk4 TrIyOix1bj39j38JKly/ocQUlaNj+SDYOIoe9Nmxwajo5DyTppbn8Hyh365wILSucjoT iVpFiWCqNCNy88fuh2AsJ71Z6LHEsHmLrneYawrSxd8e4+VllkpyFKT7+tpV0/psxMy1 GsxVPdoXof0sF7lkxlncXMathXTFhDuWxtLFHdAyv2EXnbogmLb+L4CPX9CgdTecl/me CL6w== X-Gm-Message-State: AFeK/H3YfR4632sdVu6Gd0/gd3+I4PLMbtMlT49LOXix2gItxl1XzVPoryy5O5O7TCUAaQ== X-Received: by 10.84.192.129 with SMTP id c1mr71876563pld.181.1491872298845; Mon, 10 Apr 2017 17:58:18 -0700 (PDT) Received: from aiede.mtv.corp.google.com ([2620:0:1000:5b10:dcb:fd1c:cdca:5669]) by smtp.gmail.com with ESMTPSA id a184sm15448209pfb.118.2017.04.10.17.58.18 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Mon, 10 Apr 2017 17:58:18 -0700 (PDT) Date: Mon, 10 Apr 2017 17:58:16 -0700 From: Jonathan Nieder To: Brandon Williams Cc: git@vger.kernel.org Subject: Re: [PATCH 4/5] run-command: prepare child environment before forking Message-ID: <20170411005816.GK8741@aiede.mtv.corp.google.com> References: <20170410234919.34586-1-bmwill@google.com> <20170410234919.34586-5-bmwill@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170410234919.34586-5-bmwill@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Brandon Williams wrote: > In order to avoid allocation between 'fork()' and 'exec()' prepare the > environment to be used in the child process prior to forking. If using something like posix_spawn(), this would be needed anyway, so I'll review it. [...] > +++ b/run-command.c [...] > +static char **prep_childenv(const char *const *deltaenv) > +{ > + char **childenv; > + int childenv_nr = 0, childenv_alloc = 0; > + int i; > + > + for (i = 0; environ[i]; i++) > + childenv_nr++; > + for (i = 0; deltaenv && deltaenv[i]; i++) > + childenv_alloc++; > + /* Add one for the NULL termination */ > + childenv_alloc += childenv_nr + 1; > + > + childenv = xcalloc(childenv_alloc, sizeof(char *)); > + memcpy(childenv, environ, childenv_nr * sizeof(char *)); > + > + /* merge in deltaenv */ > + for (i = 0; deltaenv && deltaenv[i]; i++) > + childenv_nr = do_putenv(childenv, childenv_nr, deltaenv[i]); > + > + return childenv; > +} This potentially copies around most of 'environ' several times as it adjusts for each deltaenv item. Can it be simplified? E.g. struct argv_array result = ARGV_ARRAY_INIT; struct string_list mods = STRING_LIST_INIT_DUP; struct strbuf key = STRBUF_INIT; const char **p; for (p = cmd_env; *p; p++) { const char *equals = strchr(*p, '='); if (equals) { strbuf_reset(&key); strbuf_add(&key, *p, equals - *p); string_list_append(&mods, key.buf)->util = *p; } else { string_list_append(&mods, *p); } } string_list_sort(&mods); for (p = environ; *p; p++) { struct string_list_item *item; const char *equals = strchr(*p, '='); if (!equals) continue; strbuf_reset(&key); strbuf_add(&key, *p, equals - *p); item = string_list_lookup(&mods, key.buf); if (!item) /* no change */ argv_array_push(&result, *p); else if (!item->util) /* unsetenv */ ; /* skip */ else /* setenv */ argv_array_push(&result, item->util); } strbuf_release(&key); string_list_clear(&mods); return argv_array_detach(&result); If the string_list API provided a lookup function taking a buffer and length as argument, the environ loop could be simplified further to use *p instead of a copy. Thanks and hope that helps, Jonathan