On Wed, May 27, 2026 at 8:56 AM David Gibson wrote: > On Tue, May 26, 2026 at 06:01:08PM +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 > > Mostly LGTM, but one query below. > > > --- > > v2: > > - Added kerneldoc for @custom_opts, @custom_opts.code, > @custom_opts.str, and @custom_opts_count in struct ctx > > - Removed len and val[255] fields from struct (moved to patch 3) > > - Removed braces from case 33, moved declarations (optcode, comma, > end) to function scope > > - Renamed code → optcode to follow function-scope convention > > --- > > conf.c | 34 +++++++++++++++++++++++++++++++++- > > passt.h | 12 ++++++++++++ > > 2 files changed, 45 insertions(+), 1 deletion(-) > > > > diff --git a/conf.c b/conf.c > > index 029b9c7..89d2127 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:"; > > @@ -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 optcode; > > 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 +1475,28 @@ 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: > > + comma = strchr(optarg, ','); > > + if (!comma) > > + die("--dhcp-opt requires Option CODE,VALUE > format"); > > + > > + optcode = strtoul(optarg, &end, 0); > > + if (end != comma || optcode < 1 || optcode > 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 = > optcode; > > What happens if the user specifies the same DHCP option code multiple > times? > > I don't know off-hand if DHCP allows the same option to be presented > multiple times; I'm guessing not. In which case we probably want to > check for already-specified options and overwrite them, instead of > adding them to the array twice. > If a user specifies the same DHCP option code multiple times, the option value is overwritten. The last specified value is considered, like if we run below command ./passt -f --dhcp-opt 6,8.8.8.8,8.8.4.4 --dhcp-opt 6,1.1.1.1,9.9.9.9 then passt DHCP option stores the last value DHCP: assign: 192.168.1.9 mask: 255.255.255.0 router: 192.168.1.1 option 6: 1.1.1.1,9.9.9.9 > > > + 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..3a0816f 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_opts: User-specified DHCP options from --dhcp-opt > > + * @custom_opts.code: DHCP option code > > + * @custom_opts.str: Original string value from command line > > + * @custom_opts_count: Number of entries in @custom_opts > > * @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_DHCP_OPTS 32 > > + > > + struct { > > + uint8_t code; > > + char str[256]; > > + } custom_opts[MAX_CUSTOM_DHCP_OPTS]; > > + int custom_opts_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 >