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-Status: No, score=-3.7 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by dcvr.yhbt.net (Postfix) with ESMTP id E2DB21FA00 for ; Tue, 16 Mar 2021 21:18:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233238AbhCPVRa (ORCPT ); Tue, 16 Mar 2021 17:17:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55842 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233155AbhCPVRV (ORCPT ); Tue, 16 Mar 2021 17:17:21 -0400 Received: from mail-wm1-x336.google.com (mail-wm1-x336.google.com [IPv6:2a00:1450:4864:20::336]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0BCAFC06174A for ; Tue, 16 Mar 2021 14:17:21 -0700 (PDT) Received: by mail-wm1-x336.google.com with SMTP id a132-20020a1c668a0000b029010f141fe7c2so19637wmc.0 for ; Tue, 16 Mar 2021 14:17:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=message-id:in-reply-to:references:from:date:subject:fcc :content-transfer-encoding:mime-version:to:cc; bh=BI76sl3lCMYZ2muS08vHRkaeFR9DdCcz1ssru/X4414=; b=AyR+VzkFQSSnCtlGUOab0DXkPzSgxax+iJhippJaUDgwMbbTSM4MmZfgpfs4ckPbIx DD1KHwg67BF3PC6r0pQqyMN4pkviLhN7owCycrykVU7M5OXuPV3Kwn7ctrfpGBRuipSd QAIwqxM/5VxR8zSWzMXgb04qM73r5ttlUZr/JOCBer8OFy+cxgN2KGsltJKhTlAx3/kI iMnRSLHrzOK8WEWBW6QoKE+yqYWVQr2G4UYc8mZYwI+XCmazA7BCtz7tNqM7HdSC3Yx0 EegI7tp1dwbr4M8XKAxWBESlA8c/PB4bsbwIlj9poEwTeZPpCUP4tE6Ql8GPWRL51I3S Bn4Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:message-id:in-reply-to:references:from:date :subject:fcc:content-transfer-encoding:mime-version:to:cc; bh=BI76sl3lCMYZ2muS08vHRkaeFR9DdCcz1ssru/X4414=; b=prmg670KpTCHAstgelpbAXVttFm+SCHQRqykqJR2DjsbwpOZ8ft9ocHju42WUbOAqi ImeZtsfFkXg66JF/2HaDxAwuPJXngFj17AeqM7Phnlzoz15R3xepzDb1YXB9FzmcObip UvSwgqAQ9u0osScEBCCIuSGcDcVjgFaHT1mIsku6pf5nrGhvfs7d1akUAyEVqJT1XUmU 3A39vAXrrfGDkb7+yQHwfyCqzdAxUDQ0T7yv2gkGCKvviLcxdqYp2X+p0Ik38IG3FEIN +mQqbJswJQJl2nBGHANrwPvYL441/qZsgdWookxVHOdSEwBmbkb3M0gRitLJFJHUkw6w A5gw== X-Gm-Message-State: AOAM530ffpS1Do6KbeBf4kxGU6CU2p39e7nAcBcHrC6zfB8oKSBGD0xM 9d61L2gWF5dRhpJiAQHyRIUluglNVWA= X-Google-Smtp-Source: ABdhPJwGpfhoUINjOSyNVZOl+GFMiUrDGA8USG5RDcrz863FO+ywnQ02Frr26A1Tf4/puiqMRm+m8A== X-Received: by 2002:a1c:7ed4:: with SMTP id z203mr622220wmc.89.1615929439854; Tue, 16 Mar 2021 14:17:19 -0700 (PDT) Received: from [127.0.0.1] ([13.74.141.28]) by smtp.gmail.com with ESMTPSA id o11sm23298428wrq.74.2021.03.16.14.17.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Mar 2021 14:17:19 -0700 (PDT) Message-Id: In-Reply-To: References: From: "Derrick Stolee via GitGitGadget" Date: Tue, 16 Mar 2021 21:16:51 +0000 Subject: [PATCH 03/27] sparse-index: API protection strategy Fcc: Sent Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit MIME-Version: 1.0 To: git@vger.kernel.org Cc: newren@gmail.com, gitster@pobox.com, Derrick Stolee , Derrick Stolee Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org From: Derrick Stolee Edit and expand the sparse-index design document with the plan for guarding index operations with ensure_full_index(). Notably, the plan has changed to not have an expand_to_path() method in favor of checking for a sparse-directory hit inside of the index_path_pos() API. The changes that follow this one will incrementally add ensure_full_index() guards to iterations over all cache entries. Some iterations over the cache entries are not protected due to a few categories listed in the document. Since these are not being modified, here is a short list of the files and methods that will not receive these guards: Looking for non-zero stage: * builtin/add.c:chmod_pathspec() * builtin/merge.c:count_unmerged_entries() * read-cache.c:unmerged_index() * rerere.c:check_one_conflict(), find_conflict(), rerere_remaining() * revision.c:prepare_show_merge() * sequencer.c:append_conflicts_hint() * wt-status.c:wt_status_collect_changes_initial() Looking for submodules: * builtin/submodule--helper.c:module_list_compute() * submodule.c: several methods * worktree.c:validate_no_submodules() Part of the index API: * name-hash.c: lazy init methods * preload-index.c:preload_thread(), preload_index() * read-cache.c: file format methods Checking for correct order of cache entries: * read-cache.c:check_ce_order() Ignores SKIP_WORKTREE entries or already aware: * unpack-trees.c:mark_new_skip_worktree() * wt-status.c:wt_status_check_sparse_checkout() Signed-off-by: Derrick Stolee --- Documentation/technical/sparse-index.txt | 32 +++++++++++++++++++++--- 1 file changed, 29 insertions(+), 3 deletions(-) diff --git a/Documentation/technical/sparse-index.txt b/Documentation/technical/sparse-index.txt index aa116406a016..7ab51bf6c441 100644 --- a/Documentation/technical/sparse-index.txt +++ b/Documentation/technical/sparse-index.txt @@ -82,9 +82,35 @@ also introduce other features that have been considered for improving the index, as well. Next, consumers of the index will be guarded against operating on a -sparse-index by inserting calls to `ensure_full_index()` or -`expand_index_to_path()`. After these guards are in place, we can begin -leaving sparse-directory entries in the in-memory index structure. +sparse-index by inserting calls to `ensure_full_index()` before iterating +over all cache entries. If a specific path is requested, then those will +be protected from within the `index_file_exists()` and `index_name_pos()` +API calls: they will call `ensure_full_index()` if necessary. + +During a scan of the codebase, not every iteration of the cache entries +needs an `ensure_full_index()` check. The basic reasons include: + +1. The loop is scanning for entries with non-zero stage. These entries + are not collapsed into a sparse-directory entry. + +2. The loop is scanning for submodules. These entries are not collapsed + into a sparse-directory entry. + +3. The loop is part of the index API, especially around reading or + writing the format. + +4. The loop is checking for correct order of cache entries and that is + correct if and only if the sparse-directory entries are in the correct + location. + +5. The loop ignores entries with the `SKIP_WORKTREE` bit set, or is + otherwise already aware of sparse directory entries. + +6. The sparse-index is disabled at this point when using the split-index + feature, so no effort is made to protect the split-index API. + +After these guards are in place, we can begin leaving sparse-directory +entries in the in-memory index structure. Even after inserting these guards, we will keep expanding sparse-indexes for most Git commands using the `command_requires_full_index` repository -- gitgitgadget