syscall: emulate Flock on AIX

    
    Reviewed-on: https://go-review.googlesource.com/79095

From-SVN: r255737

gcc/go/gofrontend/MERGE

-c02de8ca63f52a2475ce8645edee3203a3c908ac
+d1f90c9b77baca5c33a398ab844fb4440c6a5ee7
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/syscall/libcall_aix.go

@@ -111,6 +111,28 @@ func Reboot(how int) (err error) {
 //sys	Fchownat(dirfd int, path string, uid int, gid int, flags int) (err error)
 //fchownat(dirfd _C_int, path *byte, owner Uid_t, group Gid_t, flags _C_int) _C_int
 
+// On AIX, there is no flock() system call, we emulate it.
+func Flock(fd int, op int) (err error) {
+	lk := &Flock_t{}
+	if (op & LOCK_UN) != 0 {
+		lk.Type = F_UNLCK
+	} else if (op & LOCK_EX) != 0 {
+		lk.Type = F_WRLCK
+	} else if (op & LOCK_SH) != 0 {
+		lk.Type = F_RDLCK
+	} else {
+		return nil
+	}
+	if (op & LOCK_NB) != 0 {
+		err = FcntlFlock(uintptr(fd), F_SETLK, lk)
+		if err != nil && (err == EAGAIN || err == EACCES) {
+			return EWOULDBLOCK
+		}
+		return err
+	}
+	return FcntlFlock(uintptr(fd), F_SETLKW, lk)
+}
+
 //sys	Fstatfs(fd int, buf *Statfs_t) (err error)
 //fstatfs64(fd _C_int, buf *Statfs_t) _C_int