RE: [PATCH v2] tr2: log parent process name

From: "Randall S. Becker" <rsbecker@nexbridge.com>
To: "'Emily Shaffer'" <emilyshaffer@google.com>, <git@vger.kernel.org>
Cc: "'Ævar Arnfjörð Bjarmason'" <avarab@gmail.com>,
	"'Junio C Hamano'" <gitster@pobox.com>,
	"'Jeff Hostetler'" <git@jeffhostetler.com>,
	"'Bagas Sanjaya'" <bagasdotme@gmail.com>
Subject: RE: [PATCH v2] tr2: log parent process name
Date: Thu, 20 May 2021 17:36:25 -0400	[thread overview]
Message-ID: <021601d74dc0$326f6620$974e3260$@nexbridge.com> (raw)
In-Reply-To: <20210520210546.4129620-1-emilyshaffer@google.com>

On May 20, 2021 5:06 PM, Emily Shaffer wrote:
>To: git@vger.kernel.org
>Cc: Emily Shaffer <emilyshaffer@google.com>; Ævar Arnfjörð Bjarmason <avarab@gmail.com>; Junio C Hamano <gitster@pobox.com>;
>Jeff Hostetler <git@jeffhostetler.com>; Bagas Sanjaya <bagasdotme@gmail.com>
>Subject: [PATCH v2] tr2: log parent process name
>
>It can be useful to tell who invoked Git - was it invoked manually by a user via CLI or script? By an IDE?  In some cases - like 'repo' tool -
>we can influence the source code and set the GIT_TRACE2_PARENT_SID environment variable from the caller process. In 'repo''s case,
>that parent SID is manipulated to include the string "repo", which means we can positively identify when Git was invoked by 'repo' tool.
>However, identifying parents that way requires both that we know which tools invoke Git and that we have the ability to modify the source
>code of those tools. It cannot scale to keep up with the various IDEs and wrappers which use Git, most of which we don't know about.
>Learning which tools and wrappers invoke Git, and how, would give us insight to decide where to improve Git's usability and performance.
>
>Unfortunately, there's no cross-platform reliable way to gather the name of the parent process. If procfs is present, we can use that;
>otherwise we will need to discover the name another way. However, the process ID should be sufficient regardless of platform.

I like this idea, but there are some platforms where this is unlikely to work. NonStop, in particular, can initiate git - and I frequently do - from a non-POSIX environment where process name is entirely different. In fact, it is something like $ABC (always beginning with a $, which makes life very difficult for shell scripts and screws up GIT_SSH_COMMAND, but I digress). I'm going to need to plug in something very platform-specific to make this work. getppid() always returns 1 in this situation, which is extraordinarily meaningless on the platform and does not represent the actual parent.

I will try to put the appropriate compat hooks in once this moves into master but I can't promise it will be particularly efficient at this stage.

Regards,
Randall