Fix several logic bugs in the previous IPv6 variable change and

re-add $ipv6_enable support for backward compatibility.  From
UPDATING:

 1. To use IPv6, simply define $ifconfig_IF_ipv6 like $ifconfig_IF
    for IPv4.  For aliases, $ifconfig_IF_aliasN should be used.
    Note that both variables need the "inet6" keyword at the head.

    Do not set $ipv6_network_interfaces manually if you do not
    understand what you are doing.  It is not needed in most cases.

    $ipv6_ifconfig_IF and $ipv6_ifconfig_IF_aliasN still work, but
    they are obsolete.

 2. $ipv6_enable is obsolete.  Use $ipv6_prefer and/or
    "inet6 accept_rtadv" keyword in ifconfig(8) instead.

    If you define $ipv6_enable=YES, it means $ipv6_prefer=YES and
    all configured interfaces have "inet6 accept_rtadv" in the
    $ifconfig_IF_ipv6.  These are for backward compatibility.

 3. A new variable $ipv6_prefer has been added.  If NO, IPv6
    functionality of interfaces with no corresponding
    $ifconfig_IF_ipv6 is disabled by using "inet6 ifdisabled" flag,
    and the default address selection policy of ip6addrctl(8)
    is the IPv4-preferred one (see rc.d/ip6addrctl for more details).
    Note that if you want to configure IPv6 functionality on the
    disabled interfaces after boot, first you need to clear the flag by
    using ifconfig(8) like:

         ifconfig em0 inet6 -ifdisabled

    If YES, the default address selection policy is set as
    IPv6-preferred.

    The default value of $ipv6_prefer is NO.

 4. If your system need to receive Router Advertisement messages,
    define "inet6 accept_rtadv" in $ifconfig_IF_ipv6.  The rc(8)
    scripts automatically invoke rtsol(8) when the interface becomes
    UP.  The Router Advertisement messages are used for SLAAC
    (State-Less Address AutoConfiguration).

1 files changed, 72 insertions, 15 deletions

diff --git a/share/man/man5/rc.conf.5 b/share/man/man5/rc.conf.5
index 4a491f7..bacd362 100644
--- a/share/man/man5/rc.conf.5
+++ b/share/man/man5/rc.conf.5
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd September 17, 2009
+.Dd September 23, 2009
 .Dt RC.CONF 5
 .Os
 .Sh NAME
@@ -1246,28 +1246,85 @@ It is also possible to rename interface by doing:
 ifconfig_ed0_name="net0"
 ifconfig_net0="inet 192.0.2.1 netmask 0xffffff00"
 .Ed
+.It Va ipv6_enable
+.Pq Vt bool
+If the variable is
+.Dq Li YES ,
+.Dq Li inet6 accept_rtadv
+is added to all of
+.Va ifconfig_ Ns Ao Ar interface Ac Ns _ipv6
+and the
+.Va ipv6_prefer
+is defined as
+.Dq Li YES .
+.Pp
+This variable is deprecated.  Use
+.Va ipv6_prefer
+and
+.Va ifconfig_ Ns Ao Ar interface Ac Ns _ipv6 .
+.It Va ipv6_prefer
+.Pq Vt bool
+This variable does the following:
+.Pp
+If the variable is
+.Dq Li YES ,
+the default policy of the source address selection set by
+.Xr ip6addrctl 8
+will be IPv6-preferred.
+.Pp
+If the variable is
+.Dq Li NO ,
+the default policy of the source address selection set by
+.Xr ip6addrctl 8
+will be IPv4-preferred, and all of interfaces which does not have the
+corrsponding
+.Va ifconfig_ Ns Ao Ar interface Ac Ns _ipv6
+variable will be marked as
+.Dq Li IFDISABLED .
+This means only IPv6 functionality on that interface is completely
+disabled.  For more details of
+.Dq Li IFDISABLED
+flag and keywords
+.Dq Li inet6 ifdisabled ,
+see
+.Xr ifconfig 8 .
+.Pp
 .It Va ipv6_network_interfaces
 .Pq Vt str
 This is the IPv6 equivalent of
 .Va network_interfaces .
-Instead of setting the ifconfig variables as
-.Va ifconfig_ Ns Aq Ar interface
-they should be set as
-.Va ifconfig_ Ns Ao Ar interface Ac Ns _ipv6.
-Aliases should be set as
-.Va ifconfig_ Ns Ao Ar interface Ac Ns Va _alias Ns Aq Ar n .
-.Va ipv6_prefix_ Ns Aq Ar interface
-does something.
-Interfaces that have a
-.Fl accept_rtadv
-flag in
+Normally manual configuration of this variable is not needed.
+.Pp
+IPv6 functionality on an interface should be configured by
+.Va ifconfig_ Ns Ao Ar interface Ac Ns _ipv6 ,
+instead of setting ifconfig parameters in
+.Va ifconfig_ Ns Aq Ar interface .
+Aliases should be set by
+.Va ifconfig_ Ns Ao Ar interface Ac Ns Va _alias Ns Aq Ar n
+with
+.Dq Li inet6
+keyword.  For example:
+.Bd -literal
+ifconfig_ed0_ipv6="inet6 2001:db8:1::1 prefixlen 64"
+ifconfig_ed0_alias0="inet6 2001:db8:2::1 prefixlen 64"
+.Ed
+.Pp
+Interfaces that have an
+.Dq Li inet6 accept_rtadv
+keyword in
 .Va ifconfig_ Ns Ao Ar interface Ac Ns _ipv6
 setting will be automatically configured by
-.Xr rtsol 8
-if the
+.Xr rtsol 8 .
+Note that this automatic configuration is disabled if the
 .Va ipv6_gateway_enable
 is set to
-.Dq Li NO .
+.Dq Li YES .
+.It Va ipv6_prefix_ Ns Aq Ar interface
+.Pq Vt str
+If one or more prefixes are defined in
+.Va ipv6_prefix_ Ns Aq Ar interface
+addresses based on each prefix and the EUI-64 interface index will be
+configured on that interface.
 .It Va ipv6_default_interface
 .Pq Vt str
 If not set to