posixtest: fix test FcntlFlockSetLk

This test case is going to test whether the file lock works well on the
system. It firstly adds a lock and then get the lock through syscalls.
It uses F_OFD_GETLK command of fcntl(2) to get the lock info on an
opened file description[1], which is not defined on the FreeBSD. This
commit seperate the process of getting the information of lock for
different OSes, and mimic the behaviour of F_OFD_GETLK on FreeBSD.

[1]: https://www.gnu.org/software/libc/manual/html_node/Open-File-Description-Locks.html

Change-Id: I8abae0e7040fc667143eea028731e341be9b1baf

posixtest/test.go

@@ -662,12 +662,11 @@ func FcntlFlockSetLk(t *testing.T, mnt string) {
 		}
 		defer f2.Close()
 		lk := syscall.Flock_t{}
-		if err := syscall.FcntlFlock(f2.Fd(), unix.F_OFD_GETLK, &lk); err != nil {
+		if err := sysFcntlFlockGetOFDLock(f2.Fd(), &lk); err != nil {
 			t.Errorf("FcntlFlock failed: %v", err)
 		}
 		if lk.Type != syscall.F_WRLCK {
 			t.Errorf("got lk.Type=%v, want %v", lk.Type, syscall.F_WRLCK)
-
 		}
 	}
 }

posixtest/test_darwin.go

+package posixtest
+
+import "syscall"
+
+// Exist at least from macOS Siera 10.12
+const sys_F_OFD_GETLK = 92
+
+func sysFcntlFlockGetOFDLock(fd uintptr, lk *syscall.Flock_t) error {
+	return syscall.FcntlFlock(fd, sys_F_OFD_GETLK, lk)
+}

posixtest/test_freebsd.go

+package posixtest
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+// Since FreeBSD doesn't implement the F_OFD_GETLK, to mimic its behaviour,
+// we here first fork the process via syscall, and execute fcntl(2) in the child
+// process to get the lock info. Then we send the lock info via pipe back to
+// the parent test process.
+
+func sysFcntlFlockGetOFDLock(fd uintptr, lk *syscall.Flock_t) error {
+	pipefd := make([]int, 2)
+	err := syscall.Pipe(pipefd)
+	if err != nil {
+		return err
+	}
+	pid, _, err := syscall.Syscall(syscall.SYS_FORK, 0, 0, 0)
+	if pid == 0 { // child process
+		syscall.Close(pipefd[0]) // close read end
+		var clk syscall.Flock_t
+		// Here we must give a vaild lock type, or fcntl(2) will return
+		// EINVAL. And it should be different from what we set earlier
+		// in the test. Here we set to F_RDLOCK.
+		clk.Type = syscall.F_RDLCK
+		syscall.FcntlFlock(fd, syscall.F_GETLK, &clk)
+		syscall.Syscall(syscall.SYS_WRITE, uintptr(pipefd[1]), uintptr(unsafe.Pointer(&clk)), unsafe.Sizeof(clk))
+		syscall.Exit(0)
+	} else if pid > 0 { // parent process
+		syscall.Close(pipefd[1]) // close write end
+		buf := make([]byte, unsafe.Sizeof(*lk))
+		syscall.Read(pipefd[0], buf)
+		*lk = *((*syscall.Flock_t)(unsafe.Pointer(&buf[0])))
+		syscall.Close(pipefd[0]) // close read end
+	} else {
+		return err
+	}
+	return nil
+}

posixtest/test_linux.go

+package posixtest
+
+import (
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+func sysFcntlFlockGetOFDLock(fd uintptr, lk *syscall.Flock_t) error {
+	return syscall.FcntlFlock(fd, unix.F_OFD_GETLK, lk)
+}