Re: warn if GUC set to an invalid shared library

On Sat, Jan 08, 2022 at 01:29:24PM -0800, Maciek Sakrejda wrote:
> Thanks for working on this! I tried it out and it worked for me. I
> reviewed the patch and didn't see any problems, but I'm not much of a
> C programmer.

Thanks for looking at it.  I was just hacking on it myself.

Unfortunately, the output for dlopen() is not portable, which (I think) means
most of what I wrote can't be made to work..  Since it doesn't work to call
dlopen() when using SET, I tried using just stat().  But that also fails on
windows, since one of the regression tests has an invalid filename involving
unbalanced quotes, which cause it to return EINVAL rather than ENOENT.  So SET
cannot warn portably, unless it includes no details at all (or we specially
handle the windows case), or change the pre-existing regression test.  But
there's a 2nd instability, too, apparently having to do with timing.  So I'm
planning to drop the 0001 patch.

> On Tue, Dec 28, 2021 at 9:45 AM Justin Pryzby <pryzby@telsasoft.com> wrote:
> > 0002 adds context when failing to start.
> >
> >         2021-12-27 17:01:12.996 CST postmaster[1403] WARNING:  could not load library: $libdir/plugins/asdf: cannot
openshared object file: No such file or directory
 
> >         2021-12-27 17:01:14.938 CST postmaster[1403] FATAL:  could not access file "asdf": No such file or
directory
> >         2021-12-27 17:01:14.938 CST postmaster[1403] CONTEXT:  guc "shared_preload_libraries"
> >         2021-12-27 17:01:14.939 CST postmaster[1403] LOG:  database system is shut down
> 
> For whatever reason, I get slightly different (and somewhat redundant)
> output on failing to start:
> 
> 2022-01-08 12:59:36.784 PST [324482] WARNING:  could not load library: $libdir/plugins/totally bogus: cannot open
sharedobject file: No such file or directory
 
> 2022-01-08 12:59:36.787 PST [324482] FATAL:  could not load library: totally bogus: cannot open shared object file:
Nosuch file or directory
 
> 2022-01-08 12:59:36.787 PST [324482] LOG:  database system is shut down

I think the first WARNING is from the GUC mechanism "setting" the library.
And then the FATAL is from trying to apply the GUC.
It looks like you didn't apply the 0002 patch for that test so got no CONTEXT ?

$ ./tmp_install/usr/local/pgsql/bin/postgres -D src/test/regress/tmp_check/data -c shared_preload_libraries=asdf
2022-01-08 16:05:00.050 CST postmaster[2588] FATAL:  could not access file "asdf": No such file or directory
2022-01-08 16:05:00.050 CST postmaster[2588] CONTEXT:  while loading shared libraries for GUC
"shared_preload_libraries"
2022-01-08 16:05:00.050 CST postmaster[2588] LOG:  database system is shut down

-- 
Justin