[Libguestfs] [PATCH libnbd] tests: Add a test of nbd_{set, get}_socket_activation_name

[Eric Blake]

On Mon, May 08, 2023 at 09:11:03AM +0200, Laszlo Ersek wrote:
> > +
> > +  /* nbdkit doesn't know anything about socket activation names, but
> > +   * the LISTEN_FDNAMES environment variable should appear in the
> > +   * debug output.
> > +   */
> > +  assert (system ("grep 'debug.*LISTEN_FDNAMES=hello' " DEBUG_FILE) == 0);
> 
> I didn't remember the return value of system(); I've now tried to read
> up (both the Linux man page and POSIX), and my head is spinning a bit :)
> 
> It seems like we should do something like:
> 
>   int rc;
> 
>   rc = system ("grep 'debug.*LISTEN_FDNAMES=hello' " DEBUG_FILE);
>   assert (rc != -1 && WIFEXITED (rc) && WEXITSTATUS (rc) == 0);

Technically true.  But all existing implementations tend to encode
exit staus as a 16-bit value in one of two configurations:

status last: abnormal byte, status byte
status first: status byte, abnormal byte

where WIFEXITED() is a macro that returns 1 if the status byte is 0,
and WEXITSTAUTS() is a macro that masks off the abnormal byte to
expose just the status byte shifted into the usual 8-bit position.
It's not required by POSIX, but you can generally get away with
relying on 'rc==0' implies 'WIFEXITED(rc) && WEXITSTATUS(rc)==0' on
all platforms.

> 
> Also, should we invoke this "grep" with "-sq" as well (at least "-q")?
> Or do we want the match to show up in the test suite log?

Having more rather than less information in the logs can be useful
when debugging CI failures.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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