Re: [PATCH v7 05/13] conf: Allow multiple -a/--address options per address family

[Stefano Brivio <sbrivio@redhat.com>]

On Sun, 12 Apr 2026 20:53:11 -0400
Jon Maloy <jmaloy@redhat.com> wrote:

> Allow specifying multiple addresses per family with -a/--address.
> The first address of each family is used for DHCP/DHCPv6 assignment.
> 
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>

I guess it would be finally time to triumphally mention:

Link: https://bugs.passt.top/show_bug.cgi?id=47

...and Cc: its reporter on this one. :)

> ---
> v2: - Adapted to previous code changes
> v3: - Adapted to single-array strategy
>     - Changes according to feedback from S. Brivio and D. Gibson.
> v4: - Stripped down and adapted after feedback from David G.
> v6: - Adapted to previous changes in series
>     - Removed the "one address" limitation for -n option
> v7: - Updated man page.
> ---
>  conf.c  |  7 ++++---
>  fwd.c   |  4 +---
>  passt.1 |  7 +++----
>  pasta.c | 14 ++++++++------
>  4 files changed, 16 insertions(+), 16 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index 591f561..8b4a7a0 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -939,9 +939,11 @@ static void usage(const char *name, FILE *f, int status)
>  		"    default: 65520: maximum 802.3 MTU minus 802.3 header\n"
>  		"                    length, rounded to 32 bits (IPv4 words)\n"
>  		"  -a, --address ADDR	Assign IPv4 or IPv6 address ADDR[/PREFIXLEN]\n"
> -		"    can be specified zero to two times (for IPv4 and IPv6)\n"
> +		"    can be specified up to a maximum of %d times\n"
>  		"    default: use addresses from interface with default route\n"
> -		"  -n, --netmask MASK	Assign IPv4 MASK, dot-decimal or bits\n"
> +		"  -n, --netmask MASK	Assign IPv4 MASK, dot-decimal or bits\n",
> +		MAX_GUEST_ADDRS);
> +	FPRINTF(f,
>  		"    default: netmask from matching address on the host\n"
>  		"  -M, --mac-addr ADDR	Use source MAC address ADDR\n"
>  		"    default: 9a:55:9a:55:9a:55 (locally administered)\n"
> @@ -1898,7 +1900,6 @@ void conf(struct ctx *c, int argc, char **argv)
>  			    IN6_IS_ADDR_V4COMPAT(&addr.a6))
>  				die("Invalid address: %s", optarg);
>  
> -			/* Legacy behaviour: replace existing address if any */
>  			fwd_set_addr(c, &addr, CONF_ADDR_USER, prefix_len);
>  			if (inany_v4(&addr))
>  				c->ip4.no_copy_addrs = true;
> diff --git a/fwd.c b/fwd.c
> index e676c18..d3f576a 100644
> --- a/fwd.c
> +++ b/fwd.c
> @@ -250,14 +250,12 @@ void fwd_neigh_table_init(const struct ctx *c)
>  }
>  
>  /**
> - * fwd_set_addr() - Add or update an address in the unified address array
> + * fwd_set_addr() - Update address entry, adding one if needed
>   * @c:		Execution context
>   * @addr:	Address to add (IPv4-mapped or IPv6)
>   * @flags:	CONF_ADDR_* flags for this address
>   * @prefix_len:	Prefix length in IPv6 or IPv4 format
>   *
> - * Find the first existing entry of the same address family and
> - * overwrite it, or create a new one if none exists
>   */
>  void fwd_set_addr(struct ctx *c, const union inany_addr *addr,
>  		  uint8_t flags, int prefix_len)
> diff --git a/passt.1 b/passt.1
> index 13e8df9..12ec857 100644
> --- a/passt.1
> +++ b/passt.1
> @@ -164,16 +164,13 @@ An optional /\fIprefix_len\fR (0-32 for IPv4, 0-128 for IPv6) can be
>  appended in CIDR notation (e.g. 192.0.2.1/24). This is an alternative to
>  using the \fB-n\fR, \fB--netmask\fR option. Mixing CIDR notation with
>  \fB-n\fR results in an error.
> -If a prefix length is assigned to an IPv6 address using this method, it will
> -in the current code version be overridden by the default value of 64.
> -This option can be specified zero (for defaults) to two times (once for IPv4,
> -once for IPv6).
>  By default, assigned IPv4 and IPv6 addresses are taken from the host interfaces
>  with the first default route, if any, for the corresponding IP version. If no
>  default routes are available and there is any interface with any route for a
>  given IP version, the first of these interfaces will be chosen instead. If no
>  such interface exists for a given IP version, the link-local address 169.254.2.1
>  is assigned for IPv4, and no additional address will be assigned for IPv6.
> +This option can be given multiple times, indicating multiple different addresses.
>  
>  .TP
>  .BR \-n ", " \-\-netmask " " \fImask
> @@ -181,6 +178,8 @@ Assign IPv4 netmask \fImask\fR, expressed as dot-decimal or number of bits, via
>  DHCP (option 1). Alternatively, the prefix length can be specified using CIDR
>  notation with the \fB-a\fR, \fB--address\fR option (e.g. \fB-a\fR 192.0.2.1/24).
>  Mixing \fB-n\fR with CIDR notation results in an error.
> +When indicated, this option sets the prefix length of the first configured
> +IPv4 address only.
>  If no address is indicated, the netmask associated with the adopted host address,
>  if any, is used. If an address is indicated, but without a prefix length, the
>  netmask is determined based on the corresponding network class. In all other
> diff --git a/pasta.c b/pasta.c
> index c51e4cd..b3936f5 100644
> --- a/pasta.c
> +++ b/pasta.c
> @@ -343,14 +343,15 @@ void pasta_ns_conf(struct ctx *c)
>  
>  		if (c->ifi4) {
>  			if (c->ip4.no_copy_addrs) {
> -				a = fwd_get_addr(c, AF_INET, 0, 0);
> -				if (a) {
> +				for_each_addr(a, c->addrs, c->addr_count, AF_INET) {
>  					plen = inany_prefix_len(&a->addr,
>  								a->prefix_len);
>  					rc = nl_addr_set(nl_sock_ns,
>  							 c->pasta_ifi, AF_INET,
>  							 inany_v4(&a->addr),
>  							 plen);
> +					if (rc < 0)
> +						break;
>  				}
>  			} else {
>  				rc = nl_addr_dup(nl_sock, c->ifi4,
> @@ -404,13 +405,14 @@ ipv4_done:
>  					  0, IFF_NOARP);
>  
>  			if (c->ip6.no_copy_addrs) {
> -				a = fwd_get_addr(c, AF_INET6, 0, 0);
> -				if (a)
> +				for_each_addr(a, c->addrs, c->addr_count, AF_INET6) {
>  					rc = nl_addr_set(nl_sock_ns,
>  							 c->pasta_ifi,
> -							 AF_INET6,
> -							 &a->addr.a6,
> +							 AF_INET6, &a->addr.a6,
>  							 a->prefix_len);
> +					if (rc < 0)
> +						break;
> +				}
>  			} else {
>  				rc = nl_addr_dup(nl_sock, c->ifi6,
>  						 nl_sock_ns, c->pasta_ifi,

-- 
Stefano