Re: [PATCH v3 1/9] worktree: stop being overly intimate with run_command() internals
From: Eric Sunshine <hidden>
Date: 2021-11-26 09:50:27
On Thu, Nov 25, 2021 at 5:52 PM Ævar Arnfjörð Bjarmason [off-list ref] wrote:
From: Eric Sunshine <redacted> 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 people feel uncomfortable with the way this patch shadows `cp` in nested blocks, an alternative would be to call child_process_init(&cp) to reuse the existing `cp`, similar to the fix[1] applied to pager.c when reusing a `child_process`. I don't feel strongly about it either way. [1]: https://lore.kernel.org/git/20211125000239.2336-1-ematsumiya@suse.de/ (local)
quoted hunk ↗ jump to hunk
[*] 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 <redacted> Signed-off-by: Ævar Arnfjörð Bjarmason <redacted> --- builtin/worktree.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)diff --git a/builtin/worktree.c b/builtin/worktree.c index d22ece93e1a..9edd3e2829b 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()), --2.34.1.838.g779e9098efb