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From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: Enzo Matsumiya <ematsumiya@suse.de>, git@vger.kernel.org
Subject: Re: [PATCH v2] pager: fix crash when pager program doesn't exist
Date: Sun, 21 Nov 2021 23:35:51 -0500	[thread overview]
Message-ID: <YZseJ4jOVIK3+bUD@coredump.intra.peff.net> (raw)
In-Reply-To: <xmqqfsrplz3z.fsf@gitster.g>

On Sun, Nov 21, 2021 at 06:10:08PM -0800, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> > We'd usually leave of "Reviewed-by" until the reviewer has had a chance
> > to see _this_ version of the patch. I.e., usually it would not be added
> > by the submitter, but by the maintainer (unless you are resending
> > verbatim a patch that already got review).
> >
> >> diff --git a/run-command.c b/run-command.c
> >> index f329391154ae..a7bf81025afb 100644
> >> --- a/run-command.c
> >> +++ b/run-command.c
> >> @@ -19,6 +19,7 @@ void child_process_clear(struct child_process *child)
> >>  {
> >>  	strvec_clear(&child->args);
> >>  	strvec_clear(&child->env_array);
> >> +	child_process_init(child);
> >>  }
> >
> > And naturally I agree that the patch itself looks good. :)
> 
> Well, not to me X-<.  This is way too aggressive a change to be made
> lightly without auditing the current users of run_command API.

Yikes. Thanks for a dose of sanity. I was looking too much at just the
pager tests.

> It is rather common for us to reuse "struct child_process" in a code
> path, e.g. builtin/worktree.c::add_worktree() prepares a single
> instance of such a struct, sets cp.git_cmd to true, and runs either
> "update-ref" or "symbolic-ref" to update "HEAD".  After successful
> invocation of such a git subcommand, it then runs "git reset --hard",
> with this piece of code:
> 
> 	cp.git_cmd = 1;
> 
> 	if (!is_branch)
> 		strvec_pushl(&cp.args, "update-ref", "HEAD",
> 			     oid_to_hex(&commit->object.oid), NULL);
> 	else {
> 		strvec_pushl(&cp.args, "symbolic-ref", "HEAD",
> 			     symref.buf, NULL);
> 		if (opts->quiet)
> 			strvec_push(&cp.args, "--quiet");
> 	}
> 
> 	cp.env = child_env.v;
> 	ret = run_command(&cp);
> 	if (ret)
> 		goto done;
> 
> 	if (opts->checkout) {
> 		cp.argv = NULL;
> 		strvec_clear(&cp.args);
> 		strvec_pushl(&cp.args, "reset", "--hard", "--no-recurse-submodules", NULL);
> 		if (opts->quiet)
> 			strvec_push(&cp.args, "--quiet");
> 		cp.env = child_env.v;
> 		ret = run_command(&cp);
> 		if (ret)
> 			goto done;
> 	}

This is a pretty horrid interface, in that the caller has to understand
which bits of "cp" need to be adjusted: setting cp.argv to NULL, but
also potentially cp.env (if cp.env_array was used), and clearing any
stdin/out/err descriptors created as pipes in the previous command. And
probably more; that's just off the top of my head.

But clearly there's a bunch of code relying on the current state of
affairs.

> Now, we could argue that this existing caller is too lazy to assume
> that cp.git_cmd bit will be retained after run_command()
> successfully finishes and can reuse the structure without setting
> the bit again, and it should be more defensive.  And "successful
> run_command() clears the child process so that you'll get a clean
> slate" may even be a better API in the longer term.
> 
> But then a change like this one that changes the world order to make
> it a better place is also responsible to ensure that the callers are
> already following the new world order.

Yep. But I do worry a bit about changing the interface in such a subtle
way, as nothing would catch topics in flight.

> When merged to 'seen', this literally destroys tons of tests (the
> first and easiest one to observe may be t0002).

Forget 'seen'. Applying it on master shows plenty of breakages. :)

I think we should probably punt on this direction, and just make sure
that setup_pager() either reinitializes the child_process as appropriate
(as in the patch I showed in the earlier thread) or just refuses to try
running the pager twice (I didn't show a patch, but it should just be a
matter of setting a static flag).

-Peff

  reply	other threads:[~2021-11-22  4:35 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 [this message]
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
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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