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Mon, 19 Jan 2026 16:02:20 +1100 (AEDT) Date: Mon, 19 Jan 2026 16:02:12 +1100 From: David Gibson To: Jon Maloy Subject: Re: [PATCH v2 1/9] conf: Support CIDR notation for -a/--address option Message-ID: References: <20260118221612.2115386-1-jmaloy@redhat.com> <20260118221612.2115386-2-jmaloy@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="YBAQSAKRuukMURQf" Content-Disposition: inline In-Reply-To: <20260118221612.2115386-2-jmaloy@redhat.com> Message-ID-Hash: 3R5PR75FACLV4VEHSVXUWCDGQHXRVMBW X-Message-ID-Hash: 3R5PR75FACLV4VEHSVXUWCDGQHXRVMBW X-MailFrom: dgibson@gandalf.ozlabs.org X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: sbrivio@redhat.com, dgibson@redhat.com, passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: --YBAQSAKRuukMURQf Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, Jan 18, 2026 at 05:16:04PM -0500, Jon Maloy wrote: > Extend the -a/--address option to accept addresses in CIDR notation > (e.g., 192.168.1.1/24 or 2001:db8::1/64) as an alternative to using > separate -a and -n options. >=20 > We add a new conf_addr_prefix_len() helper function that: > - Parses address strings with optional /prefix_len suffix > - Validates prefix length based on address family (0-32 for IPv4, > 0-128 for IPv6), including handling of IPv4-to-IPv6 mapping case. > - Returns address family via union inany_addr output parameter >=20 > For IPv4, the prefix length is stored in ip4.prefix_len when provided. > Mixing -n and CIDR notation results in an error to catch likely user > mistakes. >=20 > Also fix a bug in conf_ip4_prefix() that was incorrectly using the > global 'optarg' instead of its 'arg' parameter. >=20 > Signed-off-by: Jon Maloy >=20 > --- > v3: Fixes after feedback from Laurent, David and Stefano > Notably, updated man page for the -a option >=20 > v4: Fixes based on feedback from David G: > - Handling prefix length adjustment when IPv4-to-IPv6 mapping > - Removed redundant !IN6_IS_ADDR_V4MAPPED(&addr.a6) test > - Simplified tests of acceptable address types > - Merged documentation and code commits > - Some documentation text clarifications > --- > conf.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++---------- > inany.c | 29 +++++++++++++++++ > inany.h | 1 + > ip.c | 21 +++++++++++++ > ip.h | 2 ++ > passt.1 | 17 +++++++--- > 6 files changed, 145 insertions(+), 22 deletions(-) >=20 > diff --git a/conf.c b/conf.c > index 2942c8c..7178a0e 100644 > --- a/conf.c > +++ b/conf.c > @@ -682,7 +682,7 @@ static int conf_ip4_prefix(const char *arg) > return -1; > } else { > errno =3D 0; > - len =3D strtoul(optarg, NULL, 0); > + len =3D strtoul(arg, NULL, 0); > if (len > 32 || errno) > return -1; > } > @@ -690,6 +690,52 @@ static int conf_ip4_prefix(const char *arg) > return len; > } > =20 > +/** > + * conf_addr_prefix_len() - Parse address with optional prefix length > + * @arg: Address string, optionally with /prefix_len suffix (modified) > + * @addr: Output for parsed address > + * @prefix_len: Output for prefix length (0 if not specified) > + * > + * Return: AF_INET for IPv4, AF_INET6 for IPv6, -1 on error > + */ > +static int conf_addr_prefix_len(char *arg, union inany_addr *addr, > + int *prefix_len) > +{ > + char *slash; > + > + *prefix_len =3D 0; > + > + /* Check for /prefix_len suffix */ > + slash =3D strchr(arg, '/'); > + if (slash) { > + unsigned long len; > + char *end; > + > + *slash =3D '\0'; > + errno =3D 0; > + len =3D strtoul(slash + 1, &end, 10); > + if (errno || *end) > + return -1; > + > + *prefix_len =3D len; > + } > + > + if (!inany_prefix_pton(arg, addr, prefix_len)) > + return -1; Oh, sorry, I wasn't clear. My idea was that inany_prefix_pton() would handle the parsing (strchr(), strtoul() etc.) of the prefix length internally, rather than doing that here then adjusting it in there. > + > + if (inany_v4(addr)) { > + if (*prefix_len > 32) > + return -1; > + > + return AF_INET; > + } > + > + if (*prefix_len > 128) > + return -1; > + > + return AF_INET6; > +} > + > /** > * conf_ip4() - Verify or detect IPv4 support, get relevant addresses > * @ifi: Host interface to attempt (0 to determine one) > @@ -896,7 +942,7 @@ static void usage(const char *name, FILE *f, int stat= us) > " a zero value disables assignment\n" > " 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\n" > + " -a, --address ADDR Assign IPv4 or IPv6 address ADDR[/PREFIXLEN]\n" > " can be specified zero to two times (for IPv4 and IPv6)\n" > " default: use addresses from interface with default route\n" > " -n, --netmask MASK Assign IPv4 MASK, dot-decimal or bits\n" > @@ -1499,6 +1545,7 @@ void conf(struct ctx *c, int argc, char **argv) > const char *logname =3D (c->mode =3D=3D MODE_PASTA) ? "pasta" : "passt"; > char userns[PATH_MAX] =3D { 0 }, netns[PATH_MAX] =3D { 0 }; > bool copy_addrs_opt =3D false, copy_routes_opt =3D false; > + bool prefix_from_cidr =3D false, prefix_from_opt =3D false; > enum fwd_ports_mode fwd_default =3D FWD_NONE; > bool v4_only =3D false, v6_only =3D false; > unsigned dns4_idx =3D 0, dns6_idx =3D 0; > @@ -1808,35 +1855,51 @@ void conf(struct ctx *c, int argc, char **argv) > c->mtu =3D mtu; > break; > } > - case 'a': > - if (inet_pton(AF_INET6, optarg, &c->ip6.addr) && > - !IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr) && > - !IN6_IS_ADDR_LOOPBACK(&c->ip6.addr) && > - !IN6_IS_ADDR_V4MAPPED(&c->ip6.addr) && > - !IN6_IS_ADDR_V4COMPAT(&c->ip6.addr) && > - !IN6_IS_ADDR_MULTICAST(&c->ip6.addr)) { > + case 'a': { > + union inany_addr addr; > + const struct in_addr *a4; > + int prefix_len =3D 0; > + int af; > + > + af =3D conf_addr_prefix_len(optarg, &addr, &prefix_len); > + > + if (inany_is_unspecified(&addr) || > + inany_is_multicast(&addr) || > + inany_is_loopback(&addr) || > + IN6_IS_ADDR_V4COMPAT(&addr.a6)) > + die("Invalid address: %s", optarg); > + > + if (af =3D=3D AF_INET6) { > + c->ip6.addr =3D addr.a6; > if (c->mode =3D=3D MODE_PASTA) > c->ip6.no_copy_addrs =3D true; > break; > } > =20 > - if (inet_pton(AF_INET, optarg, &c->ip4.addr) && > - !IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr) && > - !IN4_IS_ADDR_BROADCAST(&c->ip4.addr) && > - !IN4_IS_ADDR_LOOPBACK(&c->ip4.addr) && > - !IN4_IS_ADDR_MULTICAST(&c->ip4.addr)) { > - if (c->mode =3D=3D MODE_PASTA) > - c->ip4.no_copy_addrs =3D true; > + a4 =3D inany_v4(&addr); > + if (af =3D=3D AF_INET && a4) { > + c->ip4.addr =3D *a4; > + if (prefix_len) { > + if (prefix_from_opt) > + die("Can't mix CIDR with -n"); > + prefix_from_cidr =3D true; > + } else { > + prefix_len =3D ip4_default_prefix_len(a4); > + } > + c->ip4.prefix_len =3D prefix_len; > break; > } > =20 > die("Invalid address: %s", optarg); > break; > + } > case 'n': > + if (prefix_from_cidr) > + die("Can't use both -n and CIDR prefix length"); > c->ip4.prefix_len =3D conf_ip4_prefix(optarg); > if (c->ip4.prefix_len < 0) > die("Invalid netmask: %s", optarg); > - > + prefix_from_opt =3D true; > break; > case 'M': > parse_mac(c->our_tap_mac, optarg); > diff --git a/inany.c b/inany.c > index 7680439..f142a76 100644 > --- a/inany.c > +++ b/inany.c > @@ -57,3 +57,32 @@ int inany_pton(const char *src, union inany_addr *dst) > =20 > return 0; > } > + > +/** inany_prefix_pton - Parse an IPv[46] address with prefix length adju= stment > + * @src: IPv[46] address string > + * @dst: output buffer, filled with parsed address > + * @prefix_len: pointer to prefix length > + * > + * Return: on success, 1, if no parseable address is found, 0 > + */ > +int inany_prefix_pton(const char *src, union inany_addr *dst, int *prefi= x_len) > +{ > + /* First try parsing as plain IPv4 */ > + if (inet_pton(AF_INET, src, &dst->v4mapped.a4)) { > + memset(&dst->v4mapped.zero, 0, sizeof(dst->v4mapped.zero)); > + memset(&dst->v4mapped.one, 0xff, sizeof(dst->v4mapped.one)); > + return 1; > + } > + > + /* Try parsing as IPv6, adjust prefix length if mapped IPv4 address */ > + if (inet_pton(AF_INET6, src, &dst->a6)) { > + if (inany_v4(dst) && prefix_len && *prefix_len > 0) { > + if (*prefix_len < 96) > + return 0; > + *prefix_len -=3D 96; Because inany_addr is essentially an IPv6 representation, I think it makes more sense to always return the prefix_length as it would be for IPv6, not dependent on the address type. (So, add 96 in the inet_pton() case, rather than subtracting 96 in the explicit v4-mapped case). > + } > + return 1; > + } > + > + return 0; > +} > diff --git a/inany.h b/inany.h > index 61b36fb..36865f9 100644 > --- a/inany.h > +++ b/inany.h > @@ -295,5 +295,6 @@ static inline void inany_siphash_feed(struct siphash_= state *state, > =20 > const char *inany_ntop(const union inany_addr *src, char *dst, socklen_t= size); > int inany_pton(const char *src, union inany_addr *dst); > +int inany_prefix_pton(const char *src, union inany_addr *dst, int *prefi= x_len); > =20 > #endif /* INANY_H */ > diff --git a/ip.c b/ip.c > index 9a7f4c5..2519c71 100644 > --- a/ip.c > +++ b/ip.c > @@ -13,6 +13,8 @@ > */ > =20 > #include > +#include > + > #include "util.h" > #include "ip.h" > =20 > @@ -67,3 +69,22 @@ found: > *proto =3D nh; > return true; > } > + > +/** > + * ip4_default_prefix_len() - Get default prefix length for IPv4 address > + * @addr: IPv4 address > + * > + * Return: prefix length based on address class (8/16/24), or 32 for oth= er > + */ > +int ip4_default_prefix_len(const struct in_addr *addr) > +{ > + in_addr_t a =3D ntohl(addr->s_addr); > + > + if (IN_CLASSA(a)) > + return 8; > + if (IN_CLASSB(a)) > + return 16; > + if (IN_CLASSC(a)) > + return 24; > + return 32; > +} > diff --git a/ip.h b/ip.h > index 5830b92..e5f5198 100644 > --- a/ip.h > +++ b/ip.h > @@ -135,4 +135,6 @@ static const struct in_addr in4addr_broadcast =3D { 0= xffffffff }; > #define IPV6_MIN_MTU 1280 > #endif > =20 > +int ip4_default_prefix_len(const struct in_addr *addr); > + > #endif /* IP_H */ > diff --git a/passt.1 b/passt.1 > index db0d662..7ca03be 100644 > --- a/passt.1 > +++ b/passt.1 > @@ -156,10 +156,14 @@ By default, the advertised MTU is 65520 bytes, that= is, the maximum 802.3 MTU > minus the length of a 802.3 header, rounded to 32 bits (IPv4 words). > =20 > .TP > -.BR \-a ", " \-\-address " " \fIaddr > +.BR \-a ", " \-\-address " " \fIaddr\fR[\fB/\fR\fIprefix_len\fR] > Assign IPv4 \fIaddr\fR via DHCP (\fByiaddr\fR), or \fIaddr\fR via DHCPv6= (option > 5) and an \fIaddr\fR-based prefix via NDP Router Advertisement (option t= ype 3) > for an IPv6 \fIaddr\fR. > +An optional \fB/\fR\fIprefix_len\fR (0-32 for IPv4, 0-128 for IPv6) can = be > +appended in CIDR notation (e.g., 192.168.1.1/24). 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. > 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 int= erfaces > @@ -172,10 +176,13 @@ is assigned for IPv4, and no additional address wil= l be assigned for IPv6. > .TP > .BR \-n ", " \-\-netmask " " \fImask > Assign IPv4 netmask \fImask\fR, expressed as dot-decimal or number of bi= ts, via > -DHCP (option 1). > -By default, the netmask associated to the host address matching the assi= gned one > -is used. If there's no matching address on the host, the netmask is dete= rmined > -according to the CIDR block of the assigned address (RFC 4632). > +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 192.1= 68.1.1/24). > +Mixing \fB-n\fR with CIDR notation results in an error. > +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 o= ther > +cases, the netmask is determined by using the indicated prefix length. > =20 > .TP > .BR \-M ", " \-\-mac-addr " " \fIaddr > --=20 > 2.52.0 >=20 --=20 David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson --YBAQSAKRuukMURQf Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEO+dNsU4E3yXUXRK2zQJF27ox2GcFAmltutMACgkQzQJF27ox 2Gfgow/+MmAyNPw9p+o996dOSTR3VjSBWok651KFy/v0V38u8u++r3Qp75ZCYKN2 Z44TTr7E3vtXv1yrfBSmYK4L9f30ecsqIt1jXzt03Qi5DEfbXaVjqdY46I9cvnx0 9wH1hsH7EAAQr+1+xrDb7Ik863/2n9DIRXcwTltCp+rfzNC3hih2szmv0EioqR0j GPJHVr7tst/6k7pE3Vc0ceFK5b1nXNaczcPkhV0pYHLa71AQ7IUOo12LROysSZ1y Liab3NkEXw+TeSspDMHX0GbeW4nM1wykakGIP21cqRtoMDxvSDA3P0Nn2/z0JBwE z7/EWc16IF0DxgeK0MwCSH6hvWiYURY62j+CDT+5Q1RI0+KQl/HHFrpCga1iFDc5 wkGHxGn7p3hwggbjwzEQCHhjsroYTTZE1hopr+DyiYehMKPefR4Wf6JlsKkSULMr lv3ufuFfr9KOMFh6dp7KqHpJBQsl/DgP7yKfdeQGpD+f4oAFdIUjTVd0LBaiPKCW kqnTivR+EHcS2HMYUKo92dxkrBCymDJgm839+e7qoyMai1EwWiDBA8qLzya/COzj gw5Gurf1fhFJMF6tZFv8sf66OqHYWVuJFrErFC8M082pWboRyBuSz0uraH6yYFDI yjdrf3oPzm+2UBa5fPegqXUOOdnPO2NPFihu/Nb/yH3fjnHdlx4= =ofKI -----END PGP SIGNATURE----- --YBAQSAKRuukMURQf--