Question regarding NET_BindV6() and the "double bind"

[Xavier Roche]

Hi folks,

In the Windows version of NET_BindV6() [jdk/src/windows/native/java/net/
net_util_md.c], the code seems to be doing the binding twice when using 
a wildcard address (see b->ipv4_fd and b->ipv6_fd)

The comment says:

(..)
  * The more complicated case is when the requested address is ::0 or 
0.0.0.0.
  *
  * Two further cases:
  * 2. If the reqeusted port is 0 (ie. any port) then we try to bind in 
v4 space
  *    first with a wild-card port argument. We then try to bind in v6 space
  *    using the returned port number. If this fails, we repeat the process
  *    until a free port common to both spaces becomes available.
  *
  * 3. If the requested port is a specific port, then we just try to get 
that
  *    port in both spaces, and if it is not free in both, then the bind 
fails.

Why isn't the function simply switching IPV6_V6ONLY to "off" before 
binding ? (http://msdn.microsoft.com/en-us/library/ms738574(v=vs.85).aspx)

Such as:
     int off = 0;
     (void) setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY,
                       (char *)&off, sizeof(off));

This would allow NOT to bind two ports, and prevent any troubles with 
"half-bound" ports.

(Or am I missing something obvious ?)