On 5/21/21 4:05 PM, Emily Shaffer wrote:
On Fri, May 21, 2021 at 03:15:16PM -0400, Jeff Hostetler wrote:
On 5/20/21 5:05 PM, Emily Shaffer wrote:
- I took a look at Jeff H's advice on using a "data_json" event to log
this and decided it would be a little more flexible to add a new event
instead. If we want, it'd be feasible to then shoehorn the GfW parent
tree stuff into this new event too. Doing it this way is definitely
easier to parse for Google's trace analysis system (which for now
completely skips "data_json" as it's polymorphic), and also - I think
- means that we can add more fields later on if we need to (thread
info, different fields than just /proc/n/comm like exec path, argv,
whatever).
I could argue both sides of this, so I guess it is fine either way.
In GFW I log a array of argv[0] strings in a generic "data_json" event.
I could also log additional "data_json" events with more structured
data if needed.
On the other hand, you're proposing a "cmd_ancestry" event with a
single array of strings. You would have to expand the call signature
of the trace2_cmd_ancestry() API to add additional data and inside
tr2_tgt_event.c add additional fields to the JSON being composed.
So both are about equal.
(I'll avoid the temptation to make a snarky comment about fixing
your post processing. :-) :-) :-) )
;P
(I don't have much to add - this is an accurate summary of what I
thought about, too. Thanks for writing it out.)
It really doesn't matter one way or the other.
- Jonathan N also pointed out to me that /proc/n/comm exists, and logs
the "command name" - excluding argv, excluding path, etc. It seems
So you're trying to log argv[0] of the process and not the full
command line. That's what I'm doing.
It's close to argv[0], yeah. POSIX docs indicate it might be truncated
in a way that argv[0] hasn't been, but it also doesn't include the
leading path (as far as I've seen). For example, a long-running helper
script I use with mutt, right now (gaffing on line length in email to
help with argv clarity, sorry):
$ ps aux | grep mutt
emilysh+ 4119883 0.0 0.0 6892 3600 pts/6 S+ 12:44 0:00 /bin/bash /usr/local/google/home/emilyshaffer/dotfiles/open-vim-in-new-split.sh /var/tmp/mutt-podkayne-413244-1263002-7433772284891386689
# comm is truncated to 15ch, except apparently in the cases of some
# kernel worker processes I saw with much longer names?
$ cat /proc/4119883/comm
open-vim-in-new
# exe is a link to the executable, which means bash as this is a
# script
$ ls -lha /proc/4119883/exe
lrwxrwxrwx 1 emilyshaffer primarygroup 0 May 21 12:44
/proc/4119883/exe -> /usr/bin/bash
# cmdline has the whole argv, separated on NUL so it runs together in
# editor
$ cat /proc/4119883/cmdline
/bin/bash/usr/local/google/home/emilyshaffer/dotfiles/open-vim-in-new-split.sh/var/tmp/mutt-podkayne-413244-1263002-7433772284891386689
Jonathan N pointed out that the process name (the thing in 'comm') can
also be manually manipulated by the process itself, and 'man procfs'
also talks about 'PR_SET_NAME' and 'PR_GET_NAME' operations in
'prctl()', so that tracks. (It doesn't look like we can use prctl() to
find out the names of processes besides the current process, though, so
the procfs stuff is still needed. Dang.)
like this is a little more safe about excluding personal information
from the traces which take the form of "myscript.sh
--password=hunter2", but would still be worrisome for something like
"mysupersecretproject.sh". I'm not sure whether that means we still
want to guard it with a config flag, though.
You might check whether you get the name of the script or just get
a lot of entries with just "/usr/bin/bash".
See above :)
There's lots of PII in the data stream to worry about.
The name of the command is just one aspect, but I digress.
Yes, that's what we've noticed too, so a process name isn't worrying us
that much more.
- I also added a lot to the commit message; hopefully it's not too
rambly, but I hoped to explain why just setting GIT_TRACE2_PARENT_SID
wasn't going to cut it.
- As for testing, I followed the lead of GfW's parentage info - "this
isn't portable so writing tests for it will suck, just scrub it from
the tests". Maybe it makes sense to do some more
platform-specific-ness in the test suite instead? I wasn't sure.
yeah, that's probably best. Unless you can tokenize it properly
so that you can predict the results in a HEREDOC in the test source.
For example, you might try to test tracing a command (where a top-level
"git foo" (SPACE form) spawns a "git-foo" (DASHED form) and check the
output for the child.
Yeah, I had trouble with even deciding when to attempt such a check or
not.
+ if (reason == TRACE2_PROCESS_INFO_STARTUP)
+ {
+ /*
+ * NEEDSWORK: we could do the entire ptree in an array instead,
+ * see compat/win32/trace2_win32_process_info.c.
+ */
+ char *names[2];
+ names[0] = get_process_name(getppid());
+ names[1] = NULL;
You're only logging 1 parent. That's fine to get started.
I'm logging IIRC 10 parents on GFW. That might seem overkill,
but there are lots of intermediate parents that hide what is
happening. For example, a "git push" might spawn "git remote-https"
which spawns "git-remote-https" which spawn "git send-pack" which
spawns "git pack-objects".
And that doesn't include who called push.
And it's not uncommon to see 2 or 3 "bash" entries in the array
because of the bash scripts being run.
Agree. But it's expensive - I didn't find a handy library call to find
"parent ID of given process ID", so I think we'd have to manipulate
procfs; and so far I only see parent ID in summary infos like
/proc/n/status or /proc/n/stat, which contain lots of other info too and
would need parsing.
We could reduce the cost a little bit by grabbing the process name from
the status or stat as well, and therefore still only opening one file per
process, but I'd want to check whether the formats are expected to be
stable for those things.
Yeah, don't force it collect a bunch of data for n parents that you
don't need. I guess my point was that there were lots of time when
there were too many "unhelpful" parents in the ancestry chain. So
maybe confirm that you can get what you need from just 1 parent.
I needed more than 1 to tell that a particular command was interactive
vs launched by VS or VSCode or etc.
+static void fn_command_ancestry_fl(const char *file, int line, const char **parent_names)
+{
+ const char *event_name = "cmd_ancestry";
+ const char *parent_name = NULL;
+ struct json_writer jw = JSON_WRITER_INIT;
+
+ jw_object_begin(&jw, 0);
+ event_fmt_prepare(event_name, file, line, NULL, &jw);
+ jw_object_inline_begin_array(&jw, "ancestry");
+
+ while ((parent_name = *parent_names++))
+ jw_array_string(&jw, parent_name);
You're building the array with the immediate parent in a[0]
and the grandparent in a[1], and etc. This is the same as
I did in GFW.
Perhaps state this in the docs somewhere.
Sure, makes sense. I think I neglected any doc work whatsoever in this
patch anyways, whoops :)
+ /* cmd_ancestry parent <- grandparent <- great-grandparent */
+ strbuf_addstr(&buf_payload, "cmd_ancestry ");
+ while ((parent_name = *parent_names++)) {
+ strbuf_addstr(&buf_payload, parent_name);
Did you want to quote each parent's name?
I'd rather not - since they're going into an array anyway, I'd expect
the array delimiters to be enough. Am I being naive? 'normal' looks to
me like it's supposed to be mostly human readable anyways, rather than
parseable?
+ strbuf_addstr(&buf_payload, "ancestry:[");
+ /* It's not an argv but the rules are basically the same. */
+ sq_append_quote_argv_pretty(&buf_payload, parent_names);
This will have whitespace delimiters between the quoted strings
rather than commas. Just checking if that's what you wanted.
I'm not sure it matters, since this stream is intended for human
parsing.
Yeah, it seems fine to me as is.
We should update Documentation/technical/api-trace2.txt too.
Yep, thanks.
I appreciate the review, Jeff.
- Emily
