Re: [PATCH v5] tr2: log parent process name

[Emily Shaffer <emilyshaffer@google.com>]

On Tue, Jun 08, 2021 at 06:16:57PM -0400, Randall S. Becker wrote:
> 
> On June 8, 2021 6:11 PM, Emily Shaffer wrote:
> >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 to look up the process name on
> >most platforms, so that code may be shareable.
> >
> >Git for Windows gathers similar information and logs it as a "data_json"
> >event. However, since "data_json" has a variable format, it is difficult to parse effectively in some languages; instead, let's pursue a
> >dedicated "cmd_ancestry" event to record information about the ancestry of the current process and a consistent, parseable way.
> >
> >Git for Windows also gathers information about more than one generation of parent. In Linux further ancestry info can be gathered with
> >procfs, but it's unwieldy to do so. In the interest of later moving Git for Windows ancestry logging to the 'cmd_ancestry' event, and in the
> >interest of later adding more ancestry to the Linux implementation - or of adding this functionality to other platforms which have an
> >easier time walking the process tree - let's make 'cmd_ancestry' accept an array of parentage.
> 
> We are probably going to have to discuss this one at more length. On
> NonStop, in some cases, I have access to the program arguments of the
> parent (rather like ps -ef) in POSIX-land, but not from the other
> personality. I do have access to the program object name, in both
> sides, although if someone replaces the object - which is not actually
> possible for a running program, but a rename is - the object may end
> up being somewhat meaningless or mangled. My suspicion is that I'm
> going to have to supply different things for the two personalities,
> but I'm not sure what as of yet.

I guess I'm having trouble understanding - it sounds like you're
describing one process with a graph of ancestry instead of a line. Does
that mean we shouldn't be tracing the ancestry the way we are?

 - Emily