x/sys/unix: broken FcntlInt

[mikioh]

FcntlInt returns a non-nil error value regardless of the returned value from the system call.

// FcntlInt performs a fcntl syscall on fd with the provided command and argument.
func FcntlInt(fd uintptr, cmd, arg int) (int, error) {
	valptr, _, err := Syscall(fcntl64Syscall, fd, uintptr(cmd), uintptr(arg))
	return int(valptr), err
}

See https://go-review.googlesource.com/c/sys/+/104736 for further information.

[gopherbot]

Change https://golang.org/cl/121175 mentions this issue: unix: do not return non-nil error for 0 errno in FcntlInt

[fazalmajid]

The test is failing on one of my old OpenIndiana oi151a1 boxes, but not on newer SmartOS ones.

ok      cmd/vendor/golang.org/x/arch/x86/x86asm 0.187s
ok      cmd/vendor/golang.org/x/crypto/ssh/terminal     0.041s
--- FAIL: TestFcntlInt (0.00s)
    syscall_unix_test.go:115: flags 0x0 do not include FD_CLOEXEC
FAIL
FAIL    cmd/vendor/golang.org/x/sys/unix        0.485s
ok      cmd/vet 5.183s
ok      cmd/vet/internal/cfg    0.021s
2018/09/07 21:43:44 Failed: exit status 1
local64 ~/build>uname -a
SunOS local64.apsalar.com 5.11 oi_151a i86pc i386 i86pc

@ianlancetaylor
What's the rationale for checking that the temp file is set FD_CLOEXEC using fcntl F_GETFD? ioutil.TempFile does not set the flag (the flags passed to open() are os.O_RDWR|os.O_CREATE|os.O_EXCL but not O_CLOEXEC)

[ianlancetaylor]

@fazalmajid The os package sets FD_CLOEXEC for every file that it opens. In this case it will happen because the call to syscall.Open in openFileNoLog in os/file_unix.go adds syscall.O_CLOEXEC to the flags passed to syscall.Open. Could your OS be so old that it doesn't support passing O_CLOEXECtoopen`? And doesn't even return an error in that case?

[ianlancetaylor]

@fazalmajid In any case this should probably be discussed in a new issue as it is not related to the topic of this issue. Thanks.

[fazalmajid]

Yes, O_CLOEXEC was only added to Illumos in 2013, and the system in question dates to 2010 or 2011. It's not worth creating a new issue for OS versions that ancient.