diff --git a/include/git2/pack.h b/include/git2/pack.h index bc628c56a..b8cf77a49 100644 --- a/include/git2/pack.h +++ b/include/git2/pack.h @@ -13,7 +13,33 @@ /** * @file git2/pack.h * @brief Git pack management routines - * @defgroup git_pack Git pack management routines + * + * Packing objects + * --------------- + * + * Creation of packfiles requires two steps: + * + * - First, insert all the objects you want to put into the packfile + * using `git_packbuilder_insert` and `git_packbuilder_insert_tree`. + * It's important to add the objects in recency order ("in the order + * that they are 'reachable' from head"). + * + * "ANY order will give you a working pack, ... [but it is] the thing + * that gives packs good locality. It keeps the objects close to the + * head (whether they are old or new, but they are _reachable_ from the + * head) at the head of the pack. So packs actually have absolutely + * _wonderful_ IO patterns." - Linus Torvalds + * git.git/Documentation/technical/pack-heuristics.txt + * + * - Second, use `git_packbuilder_write` or `git_packbuilder_foreach` to + * write the resulting packfile. + * + * libgit2 will take care of the delta ordering and generation. + * `git_packbuilder_set_threads` can be used to adjust the number of + * threads used for the process. + * + * See tests-clar/pack/packbuilder.c for an example. + * * @ingroup Git * @{ */ diff --git a/tests-clar/pack/packbuilder.c b/tests-clar/pack/packbuilder.c index 513778781..84fc4d7bd 100644 --- a/tests-clar/pack/packbuilder.c +++ b/tests-clar/pack/packbuilder.c @@ -1,4 +1,6 @@ #include "clar_libgit2.h" +#include "fileops.h" +#include "hash.h" #include "iterator.h" #include "vector.h" #include "posix.h" @@ -76,6 +78,10 @@ static void seed_packbuilder(void) void test_pack_packbuilder__create_pack(void) { git_transfer_progress stats; + git_buf buf = GIT_BUF_INIT; + git_hash_ctx ctx; + git_oid hash; + char hex[41]; hex[40] = '\0'; seed_packbuilder(); cl_git_pass(git_packbuilder_write(_packbuilder, "testpack.pack")); @@ -83,6 +89,32 @@ void test_pack_packbuilder__create_pack(void) cl_git_pass(git_indexer_new(&_indexer, "testpack.pack")); cl_git_pass(git_indexer_run(_indexer, &stats)); cl_git_pass(git_indexer_write(_indexer)); + + /* + * By default, packfiles are created with only one thread. + * Therefore we can predict the object ordering and make sure + * we create exactly the same pack as git.git does when *not* + * reusing existing deltas (as libgit2). + * + * $ cd tests-clar/resources/testrepo.git + * $ git rev-list --objects HEAD | \ + * git pack-objects -q --no-reuse-delta --threads=1 pack + * $ sha1sum git-80e61eb315239ef3c53033e37fee43b744d57122.pack + * 5d410bdf97cf896f9007681b92868471d636954b + * + */ + + cl_git_pass(git_futils_readbuffer(&buf, "testpack.pack")); + + cl_git_pass(git_hash_init(&ctx)); + cl_git_pass(git_hash_update(&ctx, buf.ptr, buf.size)); + cl_git_pass(git_hash_final(&hash, &ctx)); + + git_buf_free(&buf); + + git_oid_fmt(hex, &hash); + + cl_assert_equal_s(hex, "5d410bdf97cf896f9007681b92868471d636954b"); } static git_transfer_progress stats;