[bug #52922] -Otarget does not function properly and errors on FreeBSD, with stdout to a pipe

[John Hood]

URL:
  <http://savannah.gnu.org/bugs/?52922>

                 Summary: -Otarget does not function properly and errors on
FreeBSD, with stdout to a pipe
                 Project: make
            Submitted by: cgull
            Submitted on: Thu 18 Jan 2018 02:35:34 AM UTC
                Severity: 3 - Normal
              Item Group: Bug
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: 4.2.1
        Operating System: POSIX-Based
           Fixed Release: None
           Triage Status: None

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Details:

FreeBSD 11.1, GNU Make version 4.2.1 (installed from FreeBSD packages; the
distribution patches are small and don't seem relevant here).

On this system, if GNU Make is invoked with options '-j32 -Otarget' and
standard output is redirected to a pipe, Make prints the following errors:

address@hidden:/tmp 0 $ gmake -j32 -Otarget | cat
fcntl(): Bad file descriptor
touch foo
fcntl(): Bad file descriptor
touch bar
address@hidden:/tmp 0 $ uname -a

This is because FreeBSD only supports fcntl(..., F_SETLKW, ...) on a few types
of files, including regular files and ttys.  Pipes and sockets are not
supported.

Locking for other than regular files is not required for POSIX compliance, see
http://pubs.opengroup.org/onlinepubs/9699919799/

I think the impact is fairly minimal.  The error message appears, and locking
doesn't happen, but since GNU make gathers output and writes it more
atomically in this mode, -Otarget should still mostly work.

This isn't a problem on Linux, which does seem to support F_SETLKW on pipes
and sockets at least.  I do see the problem on macOS, and I would expect that
the problem exists on most/all BSD-derived systems and probably various other
POSIX environments as well.

I don't see an obvious easy solution; I think this is intended to work with
child invocations of make, and so it's best to use a file that all of them
already have open, like stdout.  BSD systems could probably use flock()
instead, but choosing flock() over fcntl() in Configure would require figuring
out which is the better implementation on a given system.





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