Re: [PATCH 1/6] conf: Add --dhcp-opt command-line option

On Mon, 18 May 2026 18:49:57 +0530 Anshu Kumari wrote:

Introduce the --dhcp-opt flag that allows setting arbitrary DHCP options from command-line in the form of [Option CODE,VALUE]. This patch adds the option storage in struct ctx and CLI parsing; the type-aware value parser and DHCP reply injection follow in subsequent patches.

Link: https://bugs.passt.top/show_bug.cgi?id=192 Signed-off-by: Anshu Kumari --- conf.c | 36 +++++++++++++++++++++++++++++++++++- passt.h | 10 ++++++++++ 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/conf.c b/conf.c index 029b9c7..2624e58 100644 --- a/conf.c +++ b/conf.c @@ -47,6 +47,7 @@ #include "lineread.h" #include "isolation.h" #include "log.h" +#include "dhcp.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" + " --dhcp-opt CODE,VAL Set DHCP option by code\n"); if (strstr(name, "pasta")) FPRINTF(f, " default: don't use any search list\n"); else @@ -844,6 +846,10 @@ static void conf_print(const struct ctx *c) info(" router: %s", inet_ntop(AF_INET, &c->ip4.guest_gw, buf, sizeof(buf))); + for (i = 0; i < c->custom_opts_count; i++) + info(" option %u: %s", + c->custom_opts[i].code, + c->custom_opts[i].str); }

for (i = 0; i < ARRAY_SIZE(c->ip4.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' }, + {"dhcp-opt", required_argument, NULL, 33 }, { 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:"; @@ -1465,6 +1472,33 @@ 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 33: { + unsigned long code; + const char *comma; + char *end; + + comma = strchr(optarg, ','); + if (!comma) + die("--dhcp-opt requires Option CODE,VALUE format"); + + code = strtoul(optarg, &end, 0); + if (end != comma || code < 1 || code > 254) + die("DHCP option code must be 1-254: %s", + optarg); + + if (c->custom_opts_count >= MAX_CUSTOM_DHCP_OPTS) + die("Too many --dhcp-opt entries (max %d)", + MAX_CUSTOM_DHCP_OPTS); + + c->custom_opts[c->custom_opts_count].code = code; + if (snprintf_check(c->custom_opts[c->custom_opts_count].str, + sizeof(c->custom_opts[0].str), + "%s", comma + 1)) + die("DHCP option value too long: %s", + comma + 1); + c->custom_opts_count++; + break; + } case 'd': c->debug = 1; c->quiet = 0; diff --git a/passt.h b/passt.h index 1726965..acb57dd 100644 --- a/passt.h +++ b/passt.h @@ -263,6 +263,16 @@ struct ctx { char hostname[PASST_MAXDNAME]; char fqdn[PASST_MAXDNAME];

+#define MAX_CUSTOM_DHCP_OPTS 32 + + struct { + uint8_t code; + uint8_t len; + uint8_t val[255]; + char str[256]; + } custom_opts[MAX_CUSTOM_DHCP_OPTS]; + int custom_opts_count;

Assuming you actually need those fields here (but the same reasoning would apply to another struct as well): we document structs and fields (and enums, and functions) using the so-called kerneldoc style: https://docs.kernel.org/doc-guide/kernel-doc.html Just look at the beginning of struct ctx: you'll find those comments. They need to be updated when you add / change / remove fields.

+ int ifi6; struct ip6_ctx ip6;

-- Stefano