From: Eric Sunshine <sunshine@sunshineco.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: Git List <git@vger.kernel.org>,
Junio C Hamano <gitster@pobox.com>,
Emily Shaffer <emilyshaffer@google.com>
Subject: Re: [PATCH 6/6] tr2: log N parent process names on Linux
Date: Wed, 25 Aug 2021 19:49:21 -0400 [thread overview]
Message-ID: <CAPig+cShVK1OChWP+BCx-_8wPV2BKwem8vHgTdYF2gAZX0pFUQ@mail.gmail.com> (raw)
In-Reply-To: <patch-6.6-da003330800-20210825T231400Z-avarab@gmail.com>
On Wed, Aug 25, 2021 at 7:20 PM Ævar Arnfjörð Bjarmason
<avarab@gmail.com> wrote:
> [...]
> Extend the functionality added there to also log full parent chain on
> Linux. In 2f732bf15e6 it was claimed that "further ancestry info can
> be gathered with procfs, but it's unwieldy to do so.".
> [...]
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
> diff --git a/compat/linux/procinfo.c b/compat/linux/procinfo.c
> @@ -4,27 +4,129 @@
> +/*
> + * We need more complex parsing instat_parent_pid() and
s/instat_parent_pid/in stat_parent_pid/
> + * parse_proc_stat() below than a dumb fscanf(). That's because while
> + * the statcomm field is surrounded by parentheses, the process itself
> + * is free to insert any arbitrary byte sequence its its name. That
> + * can include newlines, spaces, closing parentheses etc. See
> + * do_task_stat() in fs/proc/array.c in linux.git, this is in contrast
> + * with the escaped version of the name found in /proc/%d/status.
> + *
> + * So instead of using fscanf() we'll read N bytes from it, look for
> + * the first "(", and then the last ")", anything in-between is our
> + * process name.
> + *
> + * How much N do we need? On Linux /proc/sys/kernel/pid_max is 2^15 by
> + * default, but it can be raised set to values of up to 2^22. So
> + * that's 7 digits for a PID. We have 2 PIDs in the first four fields
> + * we're interested in, so 2 * 7 = 14.
> + *
> + * We then have 4 spaces between those four values, which brings us up
> + * to 18. Add the two parentheses and it's 20. The "state" is then one
> + * character (now at 21).
> + *
> + * Finally the maximum length of the "comm" name itself is 15
> + * characters, e.g. a setting of "123456789abcdefg" will be truncated
> + * to "123456789abcdef". See PR_SET_NAME in prctl(2). So all in all
> + * we'd need to read 21 + 15 = 36 bytes.
> + *
> + * Let's just read 2^6 (64) instead for good measure. If PID_MAX ever
> + * grows past 2^22 we'll be future-proof. We'll then anchor at the
> + * last ")" we find to locate the parent PID.
> + */
next prev parent reply other threads:[~2021-08-25 23:49 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAPig+cShVK1OChWP+BCx-_8wPV2BKwem8vHgTdYF2gAZX0pFUQ@mail.gmail.com \
--to=sunshine@sunshineco.com \
--cc=avarab@gmail.com \
--cc=emilyshaffer@google.com \
--cc=git@vger.kernel.org \
--cc=gitster@pobox.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).