From: Abhishek Kumar <abhishekkumar8222@xxxxxxxxx> As discovered by Ævar, we cannot increment graph version to distinguish between generation numbers v1 and v2 [1]. Thus, one of pre-requistes before implementing generation number was to distinguish between graph versions in a backwards compatible manner. We are going to introduce a new chunk called Generation Data chunk (or GDAT). GDAT stores generation number v2 (and any subsequent versions), whereas CDAT will still store topological level. Old Git does not understand GDAT chunk and would ignore it, reading topological levels from CDAT. New Git can parse GDAT and take advantage of newer generation numbers, falling back to topological levels when GDAT chunk is missing (as it would happen with a commit graph written by old Git). We introduce a test environment variable 'GIT_TEST_COMMIT_GRAPH_NO_GDAT' which forces commit-graph file to be written without generation data chunk to emulate a commit-graph file written by old Git. [1]: https://lore.kernel.org/git/87a7gdspo4.fsf@xxxxxxxxxxxxxxxxxxx/ Signed-off-by: Abhishek Kumar <abhishekkumar8222@xxxxxxxxx> --- commit-graph.c | 48 ++++++++++++++++++++++++--- commit-graph.h | 2 ++ t/README | 3 ++ t/helper/test-read-graph.c | 2 ++ t/t4216-log-bloom.sh | 4 +-- t/t5318-commit-graph.sh | 27 +++++++-------- t/t5324-split-commit-graph.sh | 12 +++---- t/t6600-test-reach.sh | 62 +++++++++++++++++++---------------- 8 files changed, 107 insertions(+), 53 deletions(-) diff --git a/commit-graph.c b/commit-graph.c index fd69534dd5..b7a72b40db 100644 --- a/commit-graph.c +++ b/commit-graph.c @@ -38,11 +38,12 @@ void git_test_write_commit_graph_or_die(void) #define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */ #define GRAPH_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */ #define GRAPH_CHUNKID_DATA 0x43444154 /* "CDAT" */ +#define GRAPH_CHUNKID_GENERATION_DATA 0x47444154 /* "GDAT" */ #define GRAPH_CHUNKID_EXTRAEDGES 0x45444745 /* "EDGE" */ #define GRAPH_CHUNKID_BLOOMINDEXES 0x42494458 /* "BIDX" */ #define GRAPH_CHUNKID_BLOOMDATA 0x42444154 /* "BDAT" */ #define GRAPH_CHUNKID_BASE 0x42415345 /* "BASE" */ -#define MAX_NUM_CHUNKS 7 +#define MAX_NUM_CHUNKS 8 #define GRAPH_DATA_WIDTH (the_hash_algo->rawsz + 16) @@ -389,6 +390,13 @@ struct commit_graph *parse_commit_graph(void *graph_map, size_t graph_size) graph->chunk_commit_data = data + chunk_offset; break; + case GRAPH_CHUNKID_GENERATION_DATA: + if (graph->chunk_generation_data) + chunk_repeated = 1; + else + graph->chunk_generation_data = data + chunk_offset; + break; + case GRAPH_CHUNKID_EXTRAEDGES: if (graph->chunk_extra_edges) chunk_repeated = 1; @@ -755,7 +763,11 @@ static void fill_commit_graph_info(struct commit *item, struct commit_graph *g, date_low = get_be32(commit_data + g->hash_len + 12); item->date = (timestamp_t)((date_high << 32) | date_low); - graph_data->generation = get_be32(commit_data + g->hash_len + 8) >> 2; + if (g->chunk_generation_data) + graph_data->generation = item->date + + (timestamp_t) get_be32(g->chunk_generation_data + sizeof(uint32_t) * lex_index); + else + graph_data->generation = get_be32(commit_data + g->hash_len + 8) >> 2; if (g->topo_levels) *topo_level_slab_at(g->topo_levels, item) = get_be32(commit_data + g->hash_len + 8) >> 2; @@ -951,7 +963,8 @@ struct write_commit_graph_context { report_progress:1, split:1, changed_paths:1, - order_by_pack:1; + order_by_pack:1, + write_generation_data:1; struct topo_level_slab *topo_levels; const struct split_commit_graph_opts *split_opts; @@ -1106,8 +1119,25 @@ static int write_graph_chunk_data(struct hashfile *f, return 0; } +static int write_graph_chunk_generation_data(struct hashfile *f, + struct write_commit_graph_context *ctx) +{ + int i; + for (i = 0; i < ctx->commits.nr; i++) { + struct commit *c = ctx->commits.list[i]; + timestamp_t offset = commit_graph_data_at(c)->generation - c->date; + display_progress(ctx->progress, ++ctx->progress_cnt); + + if (offset > GENERATION_NUMBER_V2_OFFSET_MAX) + offset = GENERATION_NUMBER_V2_OFFSET_MAX; + hashwrite_be32(f, offset); + } + + return 0; +} + static int write_graph_chunk_extra_edges(struct hashfile *f, - struct write_commit_graph_context *ctx) + struct write_commit_graph_context *ctx) { struct commit **list = ctx->commits.list; struct commit **last = ctx->commits.list + ctx->commits.nr; @@ -1726,6 +1756,15 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx) chunks[2].id = GRAPH_CHUNKID_DATA; chunks[2].size = (hashsz + 16) * ctx->commits.nr; chunks[2].write_fn = write_graph_chunk_data; + + if (git_env_bool(GIT_TEST_COMMIT_GRAPH_NO_GDAT, 0)) + ctx->write_generation_data = 0; + if (ctx->write_generation_data) { + chunks[num_chunks].id = GRAPH_CHUNKID_GENERATION_DATA; + chunks[num_chunks].size = sizeof(uint32_t) * ctx->commits.nr; + chunks[num_chunks].write_fn = write_graph_chunk_generation_data; + num_chunks++; + } if (ctx->num_extra_edges) { chunks[num_chunks].id = GRAPH_CHUNKID_EXTRAEDGES; chunks[num_chunks].size = 4 * ctx->num_extra_edges; @@ -2130,6 +2169,7 @@ int write_commit_graph(struct object_directory *odb, ctx->split = flags & COMMIT_GRAPH_WRITE_SPLIT ? 1 : 0; ctx->split_opts = split_opts; ctx->total_bloom_filter_data_size = 0; + ctx->write_generation_data = 1; if (flags & COMMIT_GRAPH_WRITE_BLOOM_FILTERS) ctx->changed_paths = 1; diff --git a/commit-graph.h b/commit-graph.h index 1152a9642e..f78c892fc0 100644 --- a/commit-graph.h +++ b/commit-graph.h @@ -6,6 +6,7 @@ #include "oidset.h" #define GIT_TEST_COMMIT_GRAPH "GIT_TEST_COMMIT_GRAPH" +#define GIT_TEST_COMMIT_GRAPH_NO_GDAT "GIT_TEST_COMMIT_GRAPH_NO_GDAT" #define GIT_TEST_COMMIT_GRAPH_DIE_ON_PARSE "GIT_TEST_COMMIT_GRAPH_DIE_ON_PARSE" #define GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS "GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS" @@ -67,6 +68,7 @@ struct commit_graph { const uint32_t *chunk_oid_fanout; const unsigned char *chunk_oid_lookup; const unsigned char *chunk_commit_data; + const unsigned char *chunk_generation_data; const unsigned char *chunk_extra_edges; const unsigned char *chunk_base_graphs; const unsigned char *chunk_bloom_indexes; diff --git a/t/README b/t/README index 70ec61cf88..6647ef132e 100644 --- a/t/README +++ b/t/README @@ -379,6 +379,9 @@ GIT_TEST_COMMIT_GRAPH=<boolean>, when true, forces the commit-graph to be written after every 'git commit' command, and overrides the 'core.commitGraph' setting to true. +GIT_TEST_COMMIT_GRAPH_NO_GDAT=<boolean>, when true, forces the +commit-graph to be written without generation data chunk. + GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=<boolean>, when true, forces commit-graph write to compute and write changed path Bloom filters for every 'git commit-graph write', as if the `--changed-paths` option was diff --git a/t/helper/test-read-graph.c b/t/helper/test-read-graph.c index 6d0c962438..1c2a5366c7 100644 --- a/t/helper/test-read-graph.c +++ b/t/helper/test-read-graph.c @@ -32,6 +32,8 @@ int cmd__read_graph(int argc, const char **argv) printf(" oid_lookup"); if (graph->chunk_commit_data) printf(" commit_metadata"); + if (graph->chunk_generation_data) + printf(" generation_data"); if (graph->chunk_extra_edges) printf(" extra_edges"); if (graph->chunk_bloom_indexes) diff --git a/t/t4216-log-bloom.sh b/t/t4216-log-bloom.sh index c21cc160f3..55c94e9ebd 100755 --- a/t/t4216-log-bloom.sh +++ b/t/t4216-log-bloom.sh @@ -33,11 +33,11 @@ test_expect_success 'setup test - repo, commits, commit graph, log outputs' ' git commit-graph write --reachable --changed-paths ' graph_read_expect () { - NUM_CHUNKS=5 + NUM_CHUNKS=6 cat >expect <<- EOF header: 43475048 1 1 $NUM_CHUNKS 0 num_commits: $1 - chunks: oid_fanout oid_lookup commit_metadata bloom_indexes bloom_data + chunks: oid_fanout oid_lookup commit_metadata generation_data bloom_indexes bloom_data EOF test-tool read-graph >actual && test_cmp expect actual diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh index 044cf8a3de..b41b2160c6 100755 --- a/t/t5318-commit-graph.sh +++ b/t/t5318-commit-graph.sh @@ -71,7 +71,7 @@ graph_git_behavior 'no graph' full commits/3 commits/1 graph_read_expect() { OPTIONAL="" NUM_CHUNKS=3 - if test ! -z $2 + if test ! -z "$2" then OPTIONAL=" $2" NUM_CHUNKS=$((3 + $(echo "$2" | wc -w))) @@ -98,14 +98,14 @@ test_expect_success 'exit with correct error on bad input to --stdin-commits' ' # valid commit and tree OID git rev-parse HEAD HEAD^{tree} >in && git commit-graph write --stdin-commits <in && - graph_read_expect 3 + graph_read_expect 3 generation_data ' test_expect_success 'write graph' ' cd "$TRASH_DIRECTORY/full" && git commit-graph write && test_path_is_file $objdir/info/commit-graph && - graph_read_expect "3" + graph_read_expect "3" generation_data ' test_expect_success POSIXPERM 'write graph has correct permissions' ' @@ -214,7 +214,7 @@ test_expect_success 'write graph with merges' ' cd "$TRASH_DIRECTORY/full" && git commit-graph write && test_path_is_file $objdir/info/commit-graph && - graph_read_expect "10" "extra_edges" + graph_read_expect "10" "generation_data extra_edges" ' graph_git_behavior 'merge 1 vs 2' full merge/1 merge/2 @@ -249,7 +249,7 @@ test_expect_success 'write graph with new commit' ' cd "$TRASH_DIRECTORY/full" && git commit-graph write && test_path_is_file $objdir/info/commit-graph && - graph_read_expect "11" "extra_edges" + graph_read_expect "11" "generation_data extra_edges" ' graph_git_behavior 'full graph, commit 8 vs merge 1' full commits/8 merge/1 @@ -259,7 +259,7 @@ test_expect_success 'write graph with nothing new' ' cd "$TRASH_DIRECTORY/full" && git commit-graph write && test_path_is_file $objdir/info/commit-graph && - graph_read_expect "11" "extra_edges" + graph_read_expect "11" "generation_data extra_edges" ' graph_git_behavior 'cleared graph, commit 8 vs merge 1' full commits/8 merge/1 @@ -269,7 +269,7 @@ test_expect_success 'build graph from latest pack with closure' ' cd "$TRASH_DIRECTORY/full" && cat new-idx | git commit-graph write --stdin-packs && test_path_is_file $objdir/info/commit-graph && - graph_read_expect "9" "extra_edges" + graph_read_expect "9" "generation_data extra_edges" ' graph_git_behavior 'graph from pack, commit 8 vs merge 1' full commits/8 merge/1 @@ -282,7 +282,7 @@ test_expect_success 'build graph from commits with closure' ' git rev-parse merge/1 >>commits-in && cat commits-in | git commit-graph write --stdin-commits && test_path_is_file $objdir/info/commit-graph && - graph_read_expect "6" + graph_read_expect "6" "generation_data" ' graph_git_behavior 'graph from commits, commit 8 vs merge 1' full commits/8 merge/1 @@ -292,7 +292,7 @@ test_expect_success 'build graph from commits with append' ' cd "$TRASH_DIRECTORY/full" && git rev-parse merge/3 | git commit-graph write --stdin-commits --append && test_path_is_file $objdir/info/commit-graph && - graph_read_expect "10" "extra_edges" + graph_read_expect "10" "generation_data extra_edges" ' graph_git_behavior 'append graph, commit 8 vs merge 1' full commits/8 merge/1 @@ -302,7 +302,7 @@ test_expect_success 'build graph using --reachable' ' cd "$TRASH_DIRECTORY/full" && git commit-graph write --reachable && test_path_is_file $objdir/info/commit-graph && - graph_read_expect "11" "extra_edges" + graph_read_expect "11" "generation_data extra_edges" ' graph_git_behavior 'append graph, commit 8 vs merge 1' full commits/8 merge/1 @@ -323,7 +323,7 @@ test_expect_success 'write graph in bare repo' ' cd "$TRASH_DIRECTORY/bare" && git commit-graph write && test_path_is_file $baredir/info/commit-graph && - graph_read_expect "11" "extra_edges" + graph_read_expect "11" "generation_data extra_edges" ' graph_git_behavior 'bare repo with graph, commit 8 vs merge 1' bare commits/8 merge/1 @@ -420,8 +420,9 @@ test_expect_success 'replace-objects invalidates commit-graph' ' test_expect_success 'git commit-graph verify' ' cd "$TRASH_DIRECTORY/full" && - git rev-parse commits/8 | git commit-graph write --stdin-commits && - git commit-graph verify >output + git rev-parse commits/8 | GIT_TEST_COMMIT_GRAPH_NO_GDAT=1 git commit-graph write --stdin-commits && + git commit-graph verify >output && + graph_read_expect 9 extra_edges ' NUM_COMMITS=9 diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh index ea28d522b8..531016f405 100755 --- a/t/t5324-split-commit-graph.sh +++ b/t/t5324-split-commit-graph.sh @@ -13,11 +13,11 @@ test_expect_success 'setup repo' ' infodir=".git/objects/info" && graphdir="$infodir/commit-graphs" && test_oid_cache <<-EOM - shallow sha1:1760 - shallow sha256:2064 + shallow sha1:2132 + shallow sha256:2436 - base sha1:1376 - base sha256:1496 + base sha1:1408 + base sha256:1528 EOM ' @@ -28,9 +28,9 @@ graph_read_expect() { NUM_BASE=$2 fi cat >expect <<- EOF - header: 43475048 1 1 3 $NUM_BASE + header: 43475048 1 1 4 $NUM_BASE num_commits: $1 - chunks: oid_fanout oid_lookup commit_metadata + chunks: oid_fanout oid_lookup commit_metadata generation_data EOF test-tool read-graph >output && test_cmp expect output diff --git a/t/t6600-test-reach.sh b/t/t6600-test-reach.sh index 475564bee7..d14b129f06 100755 --- a/t/t6600-test-reach.sh +++ b/t/t6600-test-reach.sh @@ -55,10 +55,13 @@ test_expect_success 'setup' ' git show-ref -s commit-5-5 | git commit-graph write --stdin-commits && mv .git/objects/info/commit-graph commit-graph-half && chmod u+w commit-graph-half && + GIT_TEST_COMMIT_GRAPH_NO_GDAT=1 git commit-graph write --reachable && + mv .git/objects/info/commit-graph commit-graph-no-gdat && + chmod u+w commit-graph-no-gdat && git config core.commitGraph true ' -run_three_modes () { +run_all_modes () { test_when_finished rm -rf .git/objects/info/commit-graph && "$@" <input >actual && test_cmp expect actual && @@ -67,11 +70,14 @@ run_three_modes () { test_cmp expect actual && cp commit-graph-half .git/objects/info/commit-graph && "$@" <input >actual && + test_cmp expect actual && + cp commit-graph-no-gdat .git/objects/info/commit-graph && + "$@" <input >actual && test_cmp expect actual } -test_three_modes () { - run_three_modes test-tool reach "$@" +test_all_modes () { + run_all_modes test-tool reach "$@" } test_expect_success 'ref_newer:miss' ' @@ -80,7 +86,7 @@ test_expect_success 'ref_newer:miss' ' B:commit-4-9 EOF echo "ref_newer(A,B):0" >expect && - test_three_modes ref_newer + test_all_modes ref_newer ' test_expect_success 'ref_newer:hit' ' @@ -89,7 +95,7 @@ test_expect_success 'ref_newer:hit' ' B:commit-2-3 EOF echo "ref_newer(A,B):1" >expect && - test_three_modes ref_newer + test_all_modes ref_newer ' test_expect_success 'in_merge_bases:hit' ' @@ -98,7 +104,7 @@ test_expect_success 'in_merge_bases:hit' ' B:commit-8-8 EOF echo "in_merge_bases(A,B):1" >expect && - test_three_modes in_merge_bases + test_all_modes in_merge_bases ' test_expect_success 'in_merge_bases:miss' ' @@ -107,7 +113,7 @@ test_expect_success 'in_merge_bases:miss' ' B:commit-5-9 EOF echo "in_merge_bases(A,B):0" >expect && - test_three_modes in_merge_bases + test_all_modes in_merge_bases ' test_expect_success 'is_descendant_of:hit' ' @@ -118,7 +124,7 @@ test_expect_success 'is_descendant_of:hit' ' X:commit-1-1 EOF echo "is_descendant_of(A,X):1" >expect && - test_three_modes is_descendant_of + test_all_modes is_descendant_of ' test_expect_success 'is_descendant_of:miss' ' @@ -129,7 +135,7 @@ test_expect_success 'is_descendant_of:miss' ' X:commit-7-6 EOF echo "is_descendant_of(A,X):0" >expect && - test_three_modes is_descendant_of + test_all_modes is_descendant_of ' test_expect_success 'get_merge_bases_many' ' @@ -144,7 +150,7 @@ test_expect_success 'get_merge_bases_many' ' git rev-parse commit-5-6 \ commit-4-7 | sort } >expect && - test_three_modes get_merge_bases_many + test_all_modes get_merge_bases_many ' test_expect_success 'reduce_heads' ' @@ -166,7 +172,7 @@ test_expect_success 'reduce_heads' ' commit-2-8 \ commit-1-10 | sort } >expect && - test_three_modes reduce_heads + test_all_modes reduce_heads ' test_expect_success 'can_all_from_reach:hit' ' @@ -189,7 +195,7 @@ test_expect_success 'can_all_from_reach:hit' ' Y:commit-8-1 EOF echo "can_all_from_reach(X,Y):1" >expect && - test_three_modes can_all_from_reach + test_all_modes can_all_from_reach ' test_expect_success 'can_all_from_reach:miss' ' @@ -211,7 +217,7 @@ test_expect_success 'can_all_from_reach:miss' ' Y:commit-8-5 EOF echo "can_all_from_reach(X,Y):0" >expect && - test_three_modes can_all_from_reach + test_all_modes can_all_from_reach ' test_expect_success 'can_all_from_reach_with_flag: tags case' ' @@ -234,7 +240,7 @@ test_expect_success 'can_all_from_reach_with_flag: tags case' ' Y:commit-8-1 EOF echo "can_all_from_reach_with_flag(X,_,_,0,0):1" >expect && - test_three_modes can_all_from_reach_with_flag + test_all_modes can_all_from_reach_with_flag ' test_expect_success 'commit_contains:hit' ' @@ -250,8 +256,8 @@ test_expect_success 'commit_contains:hit' ' X:commit-9-3 EOF echo "commit_contains(_,A,X,_):1" >expect && - test_three_modes commit_contains && - test_three_modes commit_contains --tag + test_all_modes commit_contains && + test_all_modes commit_contains --tag ' test_expect_success 'commit_contains:miss' ' @@ -267,8 +273,8 @@ test_expect_success 'commit_contains:miss' ' X:commit-9-3 EOF echo "commit_contains(_,A,X,_):0" >expect && - test_three_modes commit_contains && - test_three_modes commit_contains --tag + test_all_modes commit_contains && + test_all_modes commit_contains --tag ' test_expect_success 'rev-list: basic topo-order' ' @@ -280,7 +286,7 @@ test_expect_success 'rev-list: basic topo-order' ' commit-6-2 commit-5-2 commit-4-2 commit-3-2 commit-2-2 commit-1-2 \ commit-6-1 commit-5-1 commit-4-1 commit-3-1 commit-2-1 commit-1-1 \ >expect && - run_three_modes git rev-list --topo-order commit-6-6 + run_all_modes git rev-list --topo-order commit-6-6 ' test_expect_success 'rev-list: first-parent topo-order' ' @@ -292,7 +298,7 @@ test_expect_success 'rev-list: first-parent topo-order' ' commit-6-2 \ commit-6-1 commit-5-1 commit-4-1 commit-3-1 commit-2-1 commit-1-1 \ >expect && - run_three_modes git rev-list --first-parent --topo-order commit-6-6 + run_all_modes git rev-list --first-parent --topo-order commit-6-6 ' test_expect_success 'rev-list: range topo-order' ' @@ -304,7 +310,7 @@ test_expect_success 'rev-list: range topo-order' ' commit-6-2 commit-5-2 commit-4-2 \ commit-6-1 commit-5-1 commit-4-1 \ >expect && - run_three_modes git rev-list --topo-order commit-3-3..commit-6-6 + run_all_modes git rev-list --topo-order commit-3-3..commit-6-6 ' test_expect_success 'rev-list: range topo-order' ' @@ -316,7 +322,7 @@ test_expect_success 'rev-list: range topo-order' ' commit-6-2 commit-5-2 commit-4-2 \ commit-6-1 commit-5-1 commit-4-1 \ >expect && - run_three_modes git rev-list --topo-order commit-3-8..commit-6-6 + run_all_modes git rev-list --topo-order commit-3-8..commit-6-6 ' test_expect_success 'rev-list: first-parent range topo-order' ' @@ -328,7 +334,7 @@ test_expect_success 'rev-list: first-parent range topo-order' ' commit-6-2 \ commit-6-1 commit-5-1 commit-4-1 \ >expect && - run_three_modes git rev-list --first-parent --topo-order commit-3-8..commit-6-6 + run_all_modes git rev-list --first-parent --topo-order commit-3-8..commit-6-6 ' test_expect_success 'rev-list: ancestry-path topo-order' ' @@ -338,7 +344,7 @@ test_expect_success 'rev-list: ancestry-path topo-order' ' commit-6-4 commit-5-4 commit-4-4 commit-3-4 \ commit-6-3 commit-5-3 commit-4-3 \ >expect && - run_three_modes git rev-list --topo-order --ancestry-path commit-3-3..commit-6-6 + run_all_modes git rev-list --topo-order --ancestry-path commit-3-3..commit-6-6 ' test_expect_success 'rev-list: symmetric difference topo-order' ' @@ -352,7 +358,7 @@ test_expect_success 'rev-list: symmetric difference topo-order' ' commit-3-8 commit-2-8 commit-1-8 \ commit-3-7 commit-2-7 commit-1-7 \ >expect && - run_three_modes git rev-list --topo-order commit-3-8...commit-6-6 + run_all_modes git rev-list --topo-order commit-3-8...commit-6-6 ' test_expect_success 'get_reachable_subset:all' ' @@ -372,7 +378,7 @@ test_expect_success 'get_reachable_subset:all' ' commit-1-7 \ commit-5-6 | sort ) >expect && - test_three_modes get_reachable_subset + test_all_modes get_reachable_subset ' test_expect_success 'get_reachable_subset:some' ' @@ -390,7 +396,7 @@ test_expect_success 'get_reachable_subset:some' ' git rev-parse commit-3-3 \ commit-1-7 | sort ) >expect && - test_three_modes get_reachable_subset + test_all_modes get_reachable_subset ' test_expect_success 'get_reachable_subset:none' ' @@ -404,7 +410,7 @@ test_expect_success 'get_reachable_subset:none' ' Y:commit-2-8 EOF echo "get_reachable_subset(X,Y)" >expect && - test_three_modes get_reachable_subset + test_all_modes get_reachable_subset ' test_done -- gitgitgadget
