On Thu, Jun 04, 2026 at 04:21:48PM +0530, Anshu Kumari wrote:
Add a --dhcpv6-opt CODE,VALUE option for injecting custom DHCPv6 options into server replies. This patch adds the CLI parsing in conf.c, storage in struct ctx, and a simple dhcpv6_add_option() that stores the option code and raw string value.
Signed-off-by: Anshu Kumari
Reviewed-by: David Gibson
--- conf.c | 26 +++++++++++++++++++++++++- dhcpv6.c | 37 +++++++++++++++++++++++++++++++++++++ dhcpv6.h | 1 + passt.1 | 6 ++++++ passt.h | 12 ++++++++++++ 5 files changed, 81 insertions(+), 1 deletion(-)
diff --git a/conf.c b/conf.c index 6f86940..ac7e6e5 100644 --- a/conf.c +++ b/conf.c @@ -47,6 +47,7 @@ #include "lineread.h" #include "isolation.h" #include "log.h" +#include "dhcpv6.h" #include "vhost_user.h" #include "epoll_ctl.h" #include "conf.h" @@ -616,7 +617,8 @@ static void usage(const char *name, FILE *f, int status) " -S, --search LIST Space-separated list, search domains\n" " a single, empty option disables the DNS search list\n" " -H, --hostname NAME Hostname to configure client with\n" - " --fqdn NAME FQDN to configure client with\n"); + " --fqdn NAME FQDN to configure client with\n" + " --dhcpv6-opt CODE,VAL Set DHCPv6 option by code\n"); if (strstr(name, "pasta")) FPRINTF(f, " default: don't use any search list\n"); else @@ -884,6 +886,10 @@ static void conf_print(const struct ctx *c) info(" our link-local: %s", inet_ntop(AF_INET6, &c->ip6.our_tap_ll, buf, sizeof(buf))); + for (i = 0; i < c->custom_v6opts_count; i++) + info(" v6 option %u: %s", + c->custom_v6opts[i].code, + c->custom_v6opts[i].str);
dns6: for (i = 0; i < ARRAY_SIZE(c->ip6.dns); i++) { @@ -1233,6 +1239,7 @@ void conf(struct ctx *c, int argc, char **argv) {"migrate-no-linger", no_argument, NULL, 30 }, {"stats", required_argument, NULL, 31 }, {"conf-path", required_argument, NULL, 'c' }, + {"dhcpv6-opt", required_argument, NULL, 34 }, { 0 }, }; const char *optstring = "+dqfel:hs:c:F:I:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:T:U:"; @@ -1248,10 +1255,13 @@ void conf(struct ctx *c, int argc, char **argv) uint8_t prefix_len_from_opt = 0; unsigned int ifi4 = 0, ifi6 = 0; const char *logfile = NULL; + unsigned long v6optcode; char *runas = NULL; size_t logsize = 0; + const char *comma; long fd_tap_opt; int name, ret; + char *end; uid_t uid; gid_t gid;
@@ -1465,6 +1475,20 @@ void conf(struct ctx *c, int argc, char **argv) die("Can't display statistics if not running in foreground"); c->stats = strtol(optarg, NULL, 0); break; + case 34: + comma = strchr(optarg, ','); + if (!comma) + die("--dhcpv6-opt requires CODE,VALUE format"); + + errno = 0; + v6optcode = strtoul(optarg, &end, 0); + if (end != comma || errno || + v6optcode < 1 || v6optcode > 255) + die("DHCPv6 option code must be 1-255: %s", + optarg); + + dhcpv6_add_option(c, v6optcode, comma + 1); + break; case 'd': c->debug = 1; c->quiet = 0; diff --git a/dhcpv6.c b/dhcpv6.c index 97c04e2..a0fb77c 100644 --- a/dhcpv6.c +++ b/dhcpv6.c @@ -32,6 +32,43 @@ #include "tap.h" #include "log.h"
+/** + * dhcpv6_add_option() - Add or update a custom DHCPv6 option + * @c: Execution context + * @code: DHCPv6 option code + * @val_str: Value string from command line + * + * Stores the option code and raw string value. Binary encoding and + * injection into DHCPv6 replies are handled by later patches. + * + * Return: 0 on success + */ +int dhcpv6_add_option(struct ctx *c, uint16_t code, const char *val_str) +{ + int idx; + + for (idx = 0; idx < c->custom_v6opts_count; idx++) { + if (c->custom_v6opts[idx].code == code) + break; + } + + if (idx == c->custom_v6opts_count) { + if (c->custom_v6opts_count >= MAX_CUSTOM_DHCPV6_OPTS) + die("Too many --dhcpv6-opt entries (max %d)", + MAX_CUSTOM_DHCPV6_OPTS); + c->custom_v6opts_count++; + } + + c->custom_v6opts[idx].code = code; + + if (snprintf_check(c->custom_v6opts[idx].str, + sizeof(c->custom_v6opts[0].str), + "%s", val_str)) + die("DHCPv6 option value too long: %s", val_str); + + return 0; +} + /** * struct opt_hdr - DHCPv6 option header * @t: Option type diff --git a/dhcpv6.h b/dhcpv6.h index c706dfd..c01bc36 100644 --- a/dhcpv6.h +++ b/dhcpv6.h @@ -9,5 +9,6 @@ int dhcpv6(struct ctx *c, struct iov_tail *data, struct in6_addr *saddr, struct in6_addr *daddr); void dhcpv6_init(const struct ctx *c); +int dhcpv6_add_option(struct ctx *c, uint16_t code, const char *val_str);
#endif /* DHCPV6_H */ diff --git a/passt.1 b/passt.1 index 908fd4a..9c25214 100644 --- a/passt.1 +++ b/passt.1 @@ -430,6 +430,12 @@ Send \fIname\fR as DHCP option 12 (hostname). FQDN to configure the client with. Send \fIname\fR as Client FQDN: DHCP option 81 and DHCPv6 option 39.
+.TP +.BR \-\-dhcpv6-opt " " \fICODE\fR,\fIVALUE\fR +Set a DHCPv6 option by numeric code. The value format is determined +automatically from the option code. This option can be specified multiple +times. If the same option code is given more than once, the last value wins. + .TP .BR \-t ", " \-\-tcp-ports " " \fIspec Configure TCP port forwarding to guest or namespace. \fIspec\fR can be one of: diff --git a/passt.h b/passt.h index 1726965..91509df 100644 --- a/passt.h +++ b/passt.h @@ -182,6 +182,10 @@ struct ip6_ctx { * @dns_search: DNS search list * @hostname: Guest hostname * @fqdn: Guest FQDN + * @custom_v6opts: User-specified DHCPv6 options from --dhcpv6-opt + * @custom_v6opts.code: DHCPv6 option code + * @custom_v6opts.str: Original string value from command line + * @custom_v6opts_count:Number of entries in @custom_v6opts * @ifi6: Template interface for IPv6, -1: none, 0: IPv6 disabled * @ip6: IPv6 configuration * @pasta_ifn: Name of namespace interface for pasta @@ -263,6 +267,14 @@ struct ctx { char hostname[PASST_MAXDNAME]; char fqdn[PASST_MAXDNAME];
+#define MAX_CUSTOM_DHCPV6_OPTS 32 + + struct { + uint16_t code; + char str[256]; + } custom_v6opts[MAX_CUSTOM_DHCPV6_OPTS]; + int custom_v6opts_count; + int ifi6; struct ip6_ctx ip6;
-- 2.54.0
-- 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