net_util: add support for IPv6 addresses on tap interfaces

Allow tap interfaces to be configured with an IPv6 address. The change
is fairly straightforward: we need to update the API types and CLI
parsing to accept either an IPv6 or IPv4 and then match on the IP
address type when the tap device is configured.

For IPv6 addresses, the netmask (prefix) must be provided at the same
time as the address itself (in the SIOCSIFADDR ioctl). They cannot be
configured separately. So we remove the separate "set_netmask" function
and convert "set_ip_addr" to also accept a netmask. For IPv4 addresses,
the IP address and netmask were already always set together, so this
should have no functional impact for users of IPv4 addresses.

Signed-off-by: Gregory Anders <ganders@cloudflare.com>

net_gen/src/ipv6.rs

@@ -0,0 +1,41 @@
+// Copyright © 2025 Cloud Hypervisor Authors
+//
+// SPDX-License-Identifier: Apache-2.0
+
+// bindgen /usr/include/linux/ipv6.h --no-layout-tests --constified-enum '*' --allowlist-type 'sockaddr_in6|in6_ifreq'
+
+/* automatically generated by rust-bindgen 0.71.1 */
+
+pub type __u8 = ::std::os::raw::c_uchar;
+pub type __u16 = ::std::os::raw::c_ushort;
+pub type __u32 = ::std::os::raw::c_uint;
+pub type __be16 = __u16;
+pub type __be32 = __u32;
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub struct in6_addr {
+    pub in6_u: in6_addr__bindgen_ty_1,
+}
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub union in6_addr__bindgen_ty_1 {
+    pub u6_addr8: [__u8; 16usize],
+    pub u6_addr16: [__be16; 8usize],
+    pub u6_addr32: [__be32; 4usize],
+}
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub struct sockaddr_in6 {
+    pub sin6_family: ::std::os::raw::c_ushort,
+    pub sin6_port: __be16,
+    pub sin6_flowinfo: __be32,
+    pub sin6_addr: in6_addr,
+    pub sin6_scope_id: __u32,
+}
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub struct in6_ifreq {
+    pub ifr6_addr: in6_addr,
+    pub ifr6_prefixlen: __u32,
+    pub ifr6_ifindex: ::std::os::raw::c_int,
+}

net_gen/src/lib.rs

@@ -26,6 +26,9 @@ pub mod if_tun;
 // --constified-enum '*' --with-derive-default
 // Name is "inn" to avoid conflicting with "in" keyword.
 pub mod inn;
+// generated with bindgen /usr/include/linux/ipv6.h --no-layout-tests --constified-enum '*'
+// --allowlist-type 'sockaddr_in6|in6_ifreq'
+pub mod ipv6;
 // generated with bindgen /usr/include/linux/sockios.h --no-unstable-rust
 // --constified-enum '*' --with-derive-default
 pub mod sockios;
@@ -35,6 +38,7 @@ pub use if_tun::{
 };
 pub use iff::{ifreq, net_device_flags_IFF_UP, setsockopt, sockaddr, AF_INET};
 pub use inn::sockaddr_in;
+pub use ipv6::{in6_ifreq, sockaddr_in6};
 
 pub const TUNTAP: ::std::os::raw::c_uint = 84;