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From: Emily Shaffer <emilyshaffer@google.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Jeff Hostetler" <git@jeffhostetler.com>,
	"Bagas Sanjaya" <bagasdotme@gmail.com>
Subject: Re: [PATCH v2] tr2: log parent process name
Date: Fri, 21 May 2021 12:02:29 -0700	[thread overview]
Message-ID: <YKgDxahhwK/zYznH@google.com> (raw)
In-Reply-To: <xmqqpmxksuqa.fsf@gitster.g>

On Fri, May 21, 2021 at 11:09:49AM +0900, Junio C Hamano wrote:
> 
> Emily Shaffer <emilyshaffer@google.com> writes:
> 
> > 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.
> 
> Not a strong objection, but I wonder if seeing random integer(s) is
> better than not having cmd_ancestry info at all.  The latter better
> signals that the platform does not yet have the "parent process
> name" feature, I would think.

Hm, we could; I guess then analyzers could still correlate "all these
things were called by some kind of wrapper, even if we don't know if
that was an IDE or a script or just the user or what, we can guess based
on other heuristics". Ok.

> 
> > Git for Windows also gathers information about more than one 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.
> 
> Could we rephrase "more than one parent" at the beginning to
> clarify?  I initially had to wonder what "an array of parentage"
> contains (father and mother, or a sole parent and its sole parent,
> which is a sole grandparent).  Since there is no "multiple processes
> meet and spawn a single process", I take it is the latter.  Perhaps
> "more than one generation of" or something?

Good point, will refer to "more than one generation". Thanks.

> > +	if (!strbuf_read_file(&out, procfs_path.buf, 0))
> > +	{
> 
> Place this opening brace at the end of the previous line.

Will polish up this and others for v3, hopefully today.
> > +		if (!names[0])
> > +			return;
> 
> OK, so if there is no name given, we do not show pid as a
> placeholder.

Based on your suggestion above I think it will make sense to show pid as
placeholder after all, though. So I will change that for v3.

> >  	PROCFS_EXECUTABLE_PATH = /proc/self/exe
> > +	HAVE_PROCFS_LINUX = YesPlease
> 
> Have all Linux instances procfs enabled and mounted?  It might be
> that we need to detect this at runtime anyway?
> 
>     ... goes and thinks ...
> 
> Ah, OK, that "try reading from proc/%d/comm" is the runtime
> detection, so it is only this Makefile variable is slightly
> misnamed (it is not "HAVE" but "is worth checking for it").

I wonder what is better. "MAYBE_PROCFS_LINUX"? I don't see any other
vars in config.mak.uname that indicate "pretty sure but not totally
sure" in a quick scan. However, right above this line we seem to feel
certain in our guess about "PROCFS_EXECUTABLE_PATH"...

...but when it is used in exec-cmd.c:git_get_exec_path_procfs(), invoked
by exec-cmd.c:git_get_exec_path(), we're very tolerant to faults if it's
not there:

  static int git_get_exec_path(struct strbuf *buf, const char *argv0)
  {
  	/*
  	 * [snip]
  	 * Each of these functions returns 0 on success, so evaluation will stop
  	 * after the first successful method.
  	 */
  	if (
  #ifdef HAVE_BSD_KERN_PROC_SYSCTL
  		git_get_exec_path_bsd_sysctl(buf) &&
  #endif /* HAVE_BSD_KERN_PROC_SYSCTL */
  
  #ifdef HAVE_NS_GET_EXECUTABLE_PATH
  		git_get_exec_path_darwin(buf) &&
  #endif /* HAVE_NS_GET_EXECUTABLE_PATH */
  
  #ifdef PROCFS_EXECUTABLE_PATH
  		git_get_exec_path_procfs(buf) &&  /*** <- OK if fails ***/
  #endif /* PROCFS_EXECUTABLE_PATH */
  
  #ifdef HAVE_WPGMPTR
  		git_get_exec_path_wpgmptr(buf) &&
  #endif /* HAVE_WPGMPTR */
  
  		git_get_exec_path_from_argv0(buf, argv0)) {
  		return -1;
  	}
  
  [snip]
  
  #ifdef PROCFS_EXECUTABLE_PATH
  /*
   * Resolves the executable path by examining a procfs symlink.
   *
   * Returns 0 on success, -1 on failure.
   */
  static int git_get_exec_path_procfs(struct strbuf *buf)
  {
  	if (strbuf_realpath(buf, PROCFS_EXECUTABLE_PATH, 0)) {
  		trace_printf(
  			"trace: resolved executable path from procfs: %s\n",
  			buf->buf);
  		return 0;
  	}
  	return -1;
  }
  #endif /* PROCFS_EXECUTABLE_PATH */


So it seems this other procfs bit takes the "probably but not
definitely" step and is tolerant at runtime as well. Which doesn't help
me much to decide how to rename HAVE_PROCFS_LINUX.

I'll switch it to MAYBE_PROCFS_LINUX for v3 unless someone yells, I
guess.

 - Emily

  reply	other threads:[~2021-05-21 19:02 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-07  0:29 [PATCH] tr2: log parent process name Emily Shaffer
2021-05-07  3:25 ` Bagas Sanjaya
2021-05-07 17:09 ` Emily Shaffer
2021-05-10 12:29 ` Ævar Arnfjörð Bjarmason
2021-05-11 21:31   ` Junio C Hamano
2021-05-14 22:06   ` Emily Shaffer
2021-05-16  3:48     ` Junio C Hamano
2021-05-17 20:17       ` Emily Shaffer
2021-05-11 17:28 ` Jeff Hostetler
2021-05-14 22:07   ` Emily Shaffer
2021-05-20 21:05 ` [PATCH v2] " Emily Shaffer
2021-05-20 21:36   ` Randall S. Becker
2021-05-20 23:23     ` Emily Shaffer
2021-05-21 13:20       ` Randall S. Becker
2021-05-21 16:24         ` Randall S. Becker
2021-05-21  2:09   ` Junio C Hamano
2021-05-21 19:02     ` Emily Shaffer [this message]
2021-05-21 23:22       ` Junio C Hamano
2021-05-24 18:37         ` Emily Shaffer
2021-05-21 19:15   ` Jeff Hostetler
2021-05-21 20:05     ` Emily Shaffer
2021-05-21 20:23       ` Randall S. Becker
2021-05-22 11:18       ` Jeff Hostetler
2021-05-24 23:33       ` Ævar Arnfjörð Bjarmason
2021-05-24 20:10   ` [PATCH v3] " Emily Shaffer
2021-05-24 20:49     ` Emily Shaffer
2021-05-25  3:54     ` Junio C Hamano
2021-05-25 13:33       ` Randall S. Becker
2021-06-08 18:58     ` [PATCH v4] " Emily Shaffer
2021-06-08 20:56       ` Emily Shaffer
2021-06-08 22:10       ` [PATCH v5] " Emily Shaffer
2021-06-08 22:16         ` Randall S. Becker
2021-06-08 22:24           ` Emily Shaffer
2021-06-08 22:39             ` Randall S. Becker
2021-06-09 20:17               ` Emily Shaffer
2021-06-16  8:42         ` Junio C Hamano
2021-06-28 16:45         ` Jeff Hostetler
2021-06-29 23:51           ` Emily Shaffer
2021-06-30  6:10             ` Ævar Arnfjörð Bjarmason
2021-07-22  0:21               ` Emily Shaffer
2021-07-22  1:27         ` [PATCH v6 0/2] " Emily Shaffer
2021-07-22  1:27           ` [PATCH v6 1/2] tr2: make process info collection platform-generic Emily Shaffer
2021-08-02  9:34             ` Ævar Arnfjörð Bjarmason
2021-07-22  1:27           ` [PATCH v6 2/2] tr2: log parent process name Emily Shaffer
2021-07-22 21:02             ` Junio C Hamano
2021-08-02  9:38             ` Ævar Arnfjörð Bjarmason
2021-08-02 12:45               ` Ævar Arnfjörð Bjarmason
2021-08-02 10:22             ` Ævar Arnfjörð Bjarmason
2021-08-02 12:47               ` Ævar Arnfjörð Bjarmason
2021-08-02 15:23               ` Jeff Hostetler
2021-08-02 16:10               ` Randall S. Becker
2021-08-02 18:41                 ` Ævar Arnfjörð Bjarmason
2021-08-25 23:19               ` [PATCH 0/6] tr2: plug memory leaks + logic errors + Win32 & Linux feature parity Ævar Arnfjörð Bjarmason
2021-08-25 23:19                 ` [PATCH 1/6] tr2: remove NEEDSWORK comment for "non-procfs" implementations Ævar Arnfjörð Bjarmason
2021-08-25 23:19                 ` [PATCH 2/6] tr2: clarify TRACE2_PROCESS_INFO_EXIT comment under Linux Ævar Arnfjörð Bjarmason
2021-08-25 23:19                 ` [PATCH 3/6] tr2: stop leaking "thread_name" memory Ævar Arnfjörð Bjarmason
2021-08-26  3:09                   ` Taylor Blau
2021-08-25 23:19                 ` [PATCH 4/6] tr2: fix memory leak & logic error in 2f732bf15e6 Ævar Arnfjörð Bjarmason
2021-08-26  3:21                   ` Taylor Blau
2021-08-25 23:19                 ` [PATCH 5/6] tr2: do compiler enum check in trace2_collect_process_info() Ævar Arnfjörð Bjarmason
2021-08-26  3:23                   ` Taylor Blau
2021-08-25 23:19                 ` [PATCH 6/6] tr2: log N parent process names on Linux Ævar Arnfjörð Bjarmason
2021-08-25 23:49                   ` Eric Sunshine
2021-08-26  4:07                   ` Taylor Blau
2021-08-26 12:24                     ` "I don't know what the author meant by that..." (was "Re: [PATCH 6/6] tr2: log N parent process names on Linux") Ævar Arnfjörð Bjarmason
2021-08-26 12:22                 ` [PATCH v2 0/6] tr2: plug memory leaks + logic errors + Win32 & Linux feature parity Ævar Arnfjörð Bjarmason
2021-08-26 12:22                   ` [PATCH v2 1/6] tr2: remove NEEDSWORK comment for "non-procfs" implementations Ævar Arnfjörð Bjarmason
2021-08-26 12:22                   ` [PATCH v2 2/6] tr2: clarify TRACE2_PROCESS_INFO_EXIT comment under Linux Ævar Arnfjörð Bjarmason
2021-08-26 12:22                   ` [PATCH v2 3/6] tr2: stop leaking "thread_name" memory Ævar Arnfjörð Bjarmason
2021-08-26 12:22                   ` [PATCH v2 4/6] tr2: fix memory leak & logic error in 2f732bf15e6 Ævar Arnfjörð Bjarmason
2021-08-26 15:58                     ` Eric Sunshine
2021-08-26 16:42                     ` Junio C Hamano
2021-08-26 12:22                   ` [PATCH v2 5/6] tr2: do compiler enum check in trace2_collect_process_info() Ævar Arnfjörð Bjarmason
2021-08-26 12:22                   ` [PATCH v2 6/6] tr2: log N parent process names on Linux Ævar Arnfjörð Bjarmason
2021-08-26 22:38                   ` [PATCH v2 0/6] tr2: plug memory leaks + logic errors + Win32 & Linux feature parity Taylor Blau
2021-08-27  8:02                   ` [PATCH v3 " Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 1/6] tr2: remove NEEDSWORK comment for "non-procfs" implementations Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 2/6] tr2: clarify TRACE2_PROCESS_INFO_EXIT comment under Linux Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 3/6] tr2: stop leaking "thread_name" memory Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 4/6] tr2: leave the parent list empty upon failure & don't leak memory Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 5/6] tr2: do compiler enum check in trace2_collect_process_info() Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 6/6] tr2: log N parent process names on Linux Ævar Arnfjörð Bjarmason
2021-08-31  0:17                     ` [PATCH v3 0/6] tr2: plug memory leaks + logic errors + Win32 & Linux feature parity Taylor Blau
2021-08-02 10:30             ` [PATCH v6 2/2] tr2: log parent process name Ævar Arnfjörð Bjarmason
2021-08-02 16:24               ` Junio C Hamano
2021-08-02 18:42                 ` Ævar Arnfjörð Bjarmason
2021-07-22 16:59           ` [PATCH v6 0/2] " Jeff Hostetler

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