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From: Eric Sunshine <sunshine@sunshineco.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: Git List <git@vger.kernel.org>,
	Junio C Hamano <gitster@pobox.com>, Jeff King <peff@peff.net>,
	Enzo Matsumiya <ematsumiya@suse.de>
Subject: Re: [PATCH v2 1/9] worktree: remove redundant NULL-ing of "cp.argv
Date: Wed, 24 Nov 2021 00:44:50 -0500	[thread overview]
Message-ID: <YZ3RUkGpixYAREcI@flurp.local> (raw)
In-Reply-To: <CAPig+cStZp=AOPHW8i7AqwDOV6djYzHC6GmcVeb=4PUj5bjvAw@mail.gmail.com>

On Tue, Nov 23, 2021 at 10:26:56AM -0500, Eric Sunshine wrote:
> I think perhaps the simplest thing to do is merely to squash this
> patch into the patch which ultimately removes the child_process::argv
> member (and the removal of these lines from worktree.c probably
> doesn't even need mention in the commit message -- or maybe just a
> minor mention).

On second thought, squashing this patch into the patch which
ultimately retires child_process::argv is probably not necessary. If
the patch is instead rewritten as below, then it prepares
builtin/worktree.c for eventual retirement of child_process::argv
without breaking git-worktree functionality.

(You could also extend this patch so it prepares for removal of
child_process::env, as well, or keep it minimal as I did here.)

-- >8 --
From: Eric Sunshine <sunshine@sunshineco.com>
Subject: [PATCH] worktree: stop being overly intimate with run_command()
 internals

add_worktree() reuses a `child_process` for three run_command()
invocations, but to do so, it has overly-intimate knowledge of
run-command.c internals. In particular, it knows that it must reset
child_process::argv to NULL for each subsequent invocation[*] in order
for start_command() to latch the newly-populated child_process::args for
each invocation, even though this behavior is not a part of the
documented API. Beyond having overly-intimate knowledge of run-command.c
internals, the reuse of one `child_process` for three run_command()
invocations smells like an unnecessary micro-optimization. Therefore,
stop sharing one `child_process` and instead use a new one for each
run_command() call.

[*] If child_process::argv is not reset to NULL, then subsequent
run_command() invocations will instead incorrectly access a dangling
pointer to freed memory which had been allocated by child_process::args
on the previous run. This is due to the following code in
start_command():

    if (!cmd->argv)
        cmd->argv = cmd->args.v;

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
---
 builtin/worktree.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/builtin/worktree.c b/builtin/worktree.c
index d22ece93e1..9edd3e2829 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -355,8 +355,8 @@ static int add_worktree(const char *path, const char *refname,
 		goto done;
 
 	if (opts->checkout) {
-		cp.argv = NULL;
-		strvec_clear(&cp.args);
+		struct child_process cp = CHILD_PROCESS_INIT;
+		cp.git_cmd = 1;
 		strvec_pushl(&cp.args, "reset", "--hard", "--no-recurse-submodules", NULL);
 		if (opts->quiet)
 			strvec_push(&cp.args, "--quiet");
@@ -385,12 +385,11 @@ static int add_worktree(const char *path, const char *refname,
 		const char *hook = find_hook("post-checkout");
 		if (hook) {
 			const char *env[] = { "GIT_DIR", "GIT_WORK_TREE", NULL };
-			cp.git_cmd = 0;
+			struct child_process cp = CHILD_PROCESS_INIT;
 			cp.no_stdin = 1;
 			cp.stdout_to_stderr = 1;
 			cp.dir = path;
 			cp.env = env;
-			cp.argv = NULL;
 			cp.trace2_hook_name = "post-checkout";
 			strvec_pushl(&cp.args, absolute_path(hook),
 				     oid_to_hex(null_oid()),
-- 
2.34.0.399.gdf2c515fd2

-- >8 --

  parent reply	other threads:[~2021-11-24  5:45 UTC|newest]

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-20 19:40 [PATCH v2] pager: fix crash when pager program doesn't exist Enzo Matsumiya
2021-11-21 18:37 ` Jeff King
2021-11-22  2:10   ` Junio C Hamano
2021-11-22  4:35     ` Jeff King
2021-11-22 14:52       ` Enzo Matsumiya
2021-11-22 17:05         ` Junio C Hamano
2021-11-23 16:40           ` Enzo Matsumiya
2021-11-24  1:55             ` Ævar Arnfjörð Bjarmason
2021-11-24 15:51               ` Jeff King
2021-11-22 16:04       ` [PATCH 0/5] run-command API: get rid of "argv" Ævar Arnfjörð Bjarmason
2021-11-22 16:04         ` [PATCH 1/5] archive-tar: use our own cmd.buf in error message Ævar Arnfjörð Bjarmason
2021-11-22 21:04           ` Junio C Hamano
2021-11-22 16:04         ` [PATCH 2/5] upload-archive: use regular "struct child_process" pattern Ævar Arnfjörð Bjarmason
2021-11-22 17:02           ` Jeff King
2021-11-22 20:53           ` Ævar Arnfjörð Bjarmason
2021-11-22 21:10             ` Jeff King
2021-11-22 21:36               ` Ævar Arnfjörð Bjarmason
2021-11-22 16:04         ` [PATCH 3/5] run-command API users: use strvec_pushv(), not argv assignment Ævar Arnfjörð Bjarmason
2021-11-22 21:19           ` Junio C Hamano
2021-11-22 21:30             ` Ævar Arnfjörð Bjarmason
2021-11-22 16:04         ` [PATCH 4/5] run-command API users: use strvec_pushl(), not argv construction Ævar Arnfjörð Bjarmason
2021-11-22 16:04         ` [PATCH 5/5] run-command API: remove "argv" member, always use "args" Ævar Arnfjörð Bjarmason
2021-11-22 17:32           ` Jeff King
2021-11-22 18:19             ` Ævar Arnfjörð Bjarmason
2021-11-22 18:47               ` Jeff King
2021-11-22 17:52         ` [PATCH 0/5] run-command API: get rid of "argv" Jeff King
2021-11-22 18:11           ` Junio C Hamano
2021-11-22 18:33             ` Ævar Arnfjörð Bjarmason
2021-11-22 18:49               ` Jeff King
2021-11-22 18:26           ` Ævar Arnfjörð Bjarmason
2021-11-23 12:06         ` [PATCH v2 0/9] run-command API: get rid of "argv" and "env" Ævar Arnfjörð Bjarmason
2021-11-23 12:06           ` [PATCH v2 1/9] worktree: remove redundant NULL-ing of "cp.argv Ævar Arnfjörð Bjarmason
2021-11-23 15:26             ` Eric Sunshine
2021-11-24  1:54               ` Junio C Hamano
2021-11-24  6:00                 ` Eric Sunshine
2021-11-24  6:12                   ` Eric Sunshine
2021-11-24  5:44               ` Eric Sunshine [this message]
2021-11-23 12:06           ` [PATCH v2 2/9] upload-archive: use regular "struct child_process" pattern Ævar Arnfjörð Bjarmason
2021-11-23 12:06           ` [PATCH v2 3/9] run-command API users: use strvec_pushv(), not argv assignment Ævar Arnfjörð Bjarmason
2021-11-23 12:06           ` [PATCH v2 4/9] run-command tests: " Ævar Arnfjörð Bjarmason
2021-11-24  1:33             ` Eric Sunshine
2021-11-23 12:06           ` [PATCH v2 5/9] run-command API users: use strvec_pushl(), not argv construction Ævar Arnfjörð Bjarmason
2021-11-23 12:06           ` [PATCH v2 6/9] run-command API users: use strvec_push(), " Ævar Arnfjörð Bjarmason
2021-11-23 12:06           ` [PATCH v2 7/9] run-command API: remove "argv" member, always use "args" Ævar Arnfjörð Bjarmason
2021-11-23 12:06           ` [PATCH v2 8/9] difftool: use "env_array" to simplify memory management Ævar Arnfjörð Bjarmason
2021-11-23 12:06           ` [PATCH v2 9/9] run-command API: remove "env" member, always use "env_array" Ævar Arnfjörð Bjarmason
2021-11-25 22:52           ` [PATCH v3 0/9] run-command API: get rid of "argv" and "env" Ævar Arnfjörð Bjarmason
2021-11-25 22:52             ` [PATCH v3 1/9] worktree: stop being overly intimate with run_command() internals Ævar Arnfjörð Bjarmason
2021-11-26  9:48               ` Eric Sunshine
2021-11-25 22:52             ` [PATCH v3 2/9] upload-archive: use regular "struct child_process" pattern Ævar Arnfjörð Bjarmason
2021-11-25 22:52             ` [PATCH v3 3/9] run-command API users: use strvec_pushv(), not argv assignment Ævar Arnfjörð Bjarmason
2021-11-25 22:52             ` [PATCH v3 4/9] run-command tests: " Ævar Arnfjörð Bjarmason
2021-11-25 22:52             ` [PATCH v3 5/9] run-command API users: use strvec_pushl(), not argv construction Ævar Arnfjörð Bjarmason
2021-11-25 22:52             ` [PATCH v3 6/9] run-command API users: use strvec_push(), " Ævar Arnfjörð Bjarmason
2021-11-25 22:52             ` [PATCH v3 7/9] run-command API: remove "argv" member, always use "args" Ævar Arnfjörð Bjarmason
2021-11-25 22:52             ` [PATCH v3 8/9] difftool: use "env_array" to simplify memory management Ævar Arnfjörð Bjarmason
2021-11-25 22:52             ` [PATCH v3 9/9] run-command API: remove "env" member, always use "env_array" Ævar Arnfjörð Bjarmason
2021-11-22 15:31     ` [PATCH v2] pager: fix crash when pager program doesn't exist Enzo Matsumiya
2021-11-22 16:22       ` Ævar Arnfjörð Bjarmason
2021-11-22 16:46         ` Enzo Matsumiya
2021-11-22 17:10           ` Ævar Arnfjörð Bjarmason
2021-11-22 17:41             ` Jeff King
2021-11-22 18:00             ` Junio C Hamano
2021-11-22 18:26               ` Jeff King
2021-11-22 17:55           ` Junio C Hamano
2021-11-22 18:19             ` Junio C Hamano
2021-11-22 18:37               ` Jeff King
2021-11-22 20:39                 ` Junio C Hamano
2021-11-22 17:08         ` Junio C Hamano
2021-11-22 18:35           ` Ævar Arnfjörð Bjarmason
2021-11-22 16:30       ` Jeff King

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