[PATCH] ctdb-scripts: Invoke pstree with -l option (bug 13531)

[Martin Schwenke]

Hi Amitay,

On Mon, 16 Jul 2018 14:24:05 +1000, Amitay Isaacs
<amitay at gmail.com> wrote:

> On Sun, Jul 15, 2018 at 4:46 PM, Martin Schwenke via samba-technical
> <samba-technical at lists.samba.org> wrote:
> > This should get rid of the current flappiness in various CTDB tests that
> > use the pstree command, most notably ctdb/tests/eventd/eventd_022.sh,
> > which I've seen flapping quite a bit.
> >
> > As the commit message says, a couple of recent commits have lengthened
> > the command string printed by pstree.  This, in combination with the
> > deep directory structure used by autobuild on sn-devel, is probably
> > enough to take the test the flapping point.  Then it probably comes
> > down to the width of the PID printed in the original (unfiltered)
> > pstree output. Wow!  :-)
> >
> > ... and sorry about that... you never think about these things until
> > they happen.  Who knew that pstree truncates long lines?  :-(
> >
> > I ran a private autobuild on sn-devel, running just the ctdb tests, in a
> > loop this passed 9 times in a row (until I killed it).
> >
> > Please review and maybe push...  
> 
> NACK. Let's not make commands non-portable more than necessary.

Hmmm... I thought that the version of pstree in, say, FreeBSD would be
this one:

  http://www.pell.portland.or.us/~orc/Code/ps-etc/

But it turns out that it is probably this one:

  https://www.freshports.org/sysutils/pstree

where -l means something else entirely.

> There is no real point in trying to match the output of pstree in
> tests. We have two options.
> 
> 1. Define PSTREE_CMD appropriately (this takes care of portability),
> so we can match expected output.
> 
> 2. Filter out pstree output before matching.  Easier done in eventd
> tests as we can just drop pstree command from debug-script.sh.
> 
> We can pick 1 or 2, or some combination of 1 and 2.

I wouldn't like to lose all of the pstree output.  If for some reason
something changes and the test fails then that output almost certainly
provides enough information to understand why.

Perhaps something like the following is good enough to show the event
script and immediate children?

$ ps -e -o pid,ppid,args | awk -v pid=$$ '$1 == pid || $2 == pid { print }'
 9115  1642 bash
10487  9115 ps -e -o pid,ppid,args
10488  9115 awk -v pid=9115 $1 == pid || $2 == pid { print }

I've used $$, which illustrates it well, but we would obviously use
"$pid" or similar.

As far as I can tell the above is completely POSIX-complaint.

I've tried adding -f.  With both that and -e Linux ps prints the
environment along with each command, which doesn't make sense, since -e
is only supposed to influence process selection.

Do you think the above gives us what we need and is sufficiently
portable?

peace & happiness,
martin