Re: [PATCH 10/10] submodule: don't use a subprocess to invoke "submodule--helper"
From: Glen Choo <hidden>
Date: 2022-10-20 23:19:03
Ævar Arnfjörð Bjarmason [off-list ref] writes:
In a preceding commit we created "builtin/submodule.c" and faithfully tried to reproduce every aspect of "git-submodule.sh", including its invocation of "git submodule--helper" as a sub-process. Let's do away with the sub-process and invoke "cmd_submodule__helper()" directly. Eventually we'll want to do away with "builtin/submodule--helper.c" altogether, but let's not do that for now to avoid conflicts with other in-flight topics. Even without those conflicts the resulting diff would be large. We can leave that for a later cleanup.
Thanks! e.g. this managed to avoid conflicts with my newly sent out "submodule clone with branches" v2 [1] [1] https://lore.kernel.org/git/pull.1321.v2.git.git.1666297238.gitgitgadget@gmail.com (local)
It's also worth noting that some users were using e.g. "git submodule--helper list" directly for performance reasons[2]. With 31955475d1c (submodule--helper: remove unused "list" helper, 2022-09-01) released with v2.38.0 the "list" command was no longer provided.
[...]
I think it would make sense to implement a "--format" option for "git submodule foreach" to help anyone who cares about that remaining performance (and to improve the API, e.g. by supporting "-z"), but as far as performance goes this makes the runtime acceptable again.
FWIW, I don't think that dropping "git submodule--helper list" was a mistake, since all of "git submodule--helper" was meant to be internal anyway. But if users find it useful, we could add actually supported functionality like what you propose here.
The pattern in "cmd_submodule_builtin()" of saving "struct strvec" arguments to a "struct string_list" and free()-ing them after the "argv" has been modified by "cmd_submodule__helper()" is new, without it we'd get various already-passing tests failing under SANITIZE=leak.
[...]
+static int cmd_submodule_builtin(struct strvec *args, const char *prefix)
+{
+ size_t i;
+ struct string_list to_free = STRING_LIST_INIT_DUP;
+ int ret;
+
+ /*
+ * The cmd_submodule__helper() will treat the argv as
+ * its own and modify it, so e.g. for "git submodule
+ * add" the "add" argument will be removed, and we'll
+ * thus leak from the strvec_push()'s in
+ * setup_helper_args().
+ *
+ * So in lieu of some generic "snapshot for a free"
+ * API for "struct strvec" squirrel away the pointers
+ * to free with string_list_clear() later.
+ */
+ for (i = 0; i < args->nr; i++)
+ string_list_append_nodup(&to_free, (char *)args->v[i]);
+
+ ret = cmd_submodule__helper(args->nr, args->v, prefix);
+
+ string_list_clear(&to_free, 0);Hm, so this trick works because we init STRING_LIST_INIT_DUP to make the string_list think that it owns its strings, but when we append, we use string_list_append_nodup(), which doesn't dup the strings. This 'moves' the strings into the string_list and causes them to be freed when we call string_list_clear(). Sounds reasonable enough to me, but I'm not an expert on leaks :)
quoted hunk ↗ jump to hunk
+ free(strvec_detach(args)); + + return ret; +} + int cmd_submodule(int argc, const char **argv, const char *prefix) { int opt_quiet = 0; int opt_cached = 0; int opt_recursive = 0; - struct child_process cp = CHILD_PROCESS_INIT; + struct strvec args = STRVEC_INIT; struct option options[] = { OPT__QUIET(&opt_quiet, N_("be quiet")), OPT_BOOL(0, "cached", &opt_cached,@@ -141,13 +169,10 @@ int cmd_submodule(int argc, const char **argv, const char *prefix) * Tell the rest of git that any URLs we get don't come * directly from the user, so it can apply policy as appropriate. */ - strvec_push(&cp.env, "GIT_PROTOCOL_FROM_USER=0"); - setup_helper_args(argc, argv, prefix, opt_quiet, opt_cached, - opt_recursive, &cp.args, options); + xsetenv("GIT_PROTOCOL_FROM_USER", "0", 1); - cp.git_cmd = 1; - cp.no_stdin = 0; /* for git submodule foreach */ - cp.dir = startup_info->original_cwd; + setup_helper_args(argc, argv, prefix, opt_quiet, opt_cached, + opt_recursive, &args, options); - return run_command(&cp); + return cmd_submodule_builtin(&args, prefix); }-- 2.38.0.1091.gf9d18265e59