Re: [PATCH] tr2: log parent process name

On Tue, May 11, 2021 at 01:28:39PM -0400, Jeff Hostetler wrote:

On 5/6/21 8:29 PM, Emily Shaffer wrote:

quoted

It can be useful to tell who invoked Git - was it invoked manually by a
user via CLI or script? By an IDE? Knowing where the Git invocation came
from can help with debugging to isolate where the problem came from.

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.

Signed-off-by: Emily Shaffer <redacted>
---
We briefly discussed hiding this behind a config, internally. However, I
wanted to include the parent name alongside the cmd_start event, which
happens very early (maybe before config gathering?).

Maybe it's better to log the parent_name as its own event, since it
shouldn't change over the lifetime of the process?

procfs is very non-portable, though - I think this won't even work on
MacOS. So I'm curious if anybody has better suggestions for how to do
this.

  - Emily

Look at `trace2_collect_process_info()` in `trace2.h` and
`compat/win32/trace2_win32_process_info.c`.

That function is designed to let the process call out to
platform-specific code to do things like getting the name
of the invoking process.

It is called with an enum to indicate when/why it is being
called.

On Windows, I have platform code to get the process ancestry,
the peak VM usage, and whether the process is being debugged.
Two of those were easy....  And all are very platform-specific.

They all generate events of the form:

	trace2_data_*("process", "windows/<something>", ...)

Some of my `t021[012]/` helper scripts exclude "process" category
messages from the output to make the t*.sh tests portable.


To implement a /proc lookup as you have suggested, I would
fixup the Makefile or config.mak.uname to include something
like a "HAVE_..." feature and then use that at the
bottom of trace2.h to declare a trace2_collect_process_info()
function and then have your code in compat/procinfo.c hide
behind my interface.

Your code should emits events of the form:

	trace2_data_*("process", "linux/<something>", ...)

I notice there are several `PROCFS_*` symbols currently defined
in `config.mak.uname` so maybe this should be:

	trace2_data_*("process", "procfs/<something>", ...)

(I'm not sure how similar code for Linux and the various BSD
versions would be.)

Thanks a bunch for the pointers - this is great.

 - Emily