Re: [PATCH v6 2/6] dhcp: Add option state management with enum opt_state

On 8/24/26 15:44, Anshu Kumari wrote:

Overloading slen = -1 to mean "not set" conflates the option length with its lifecycle state, and can't express additional states such as "set by the user via command-line" which will be needed for --dhcp-opt support.

Introduce enum opt_state with OPT_UNSET (option not configured) and OPT_DEFAULT (derived from host configuration). Replace all slen = -1 / slen != -1 checks with state comparisons, and set state = OPT_DEFAULT for options initialised in dhcp_init() and at reply time in dhcp().

Link: https://bugs.passt.top/show_bug.cgi?id=192 Signed-off-by: Anshu Kumari --- v6: - Rewrote commit message to explain why slen = -1 overloading is problematic and how it motivates the enum. - Dropped explicit OPT_UNSET initialization loop inside dhcp_init(). - Realigned opts[51] initializer for consistency.

v5: - New patch: introduce enum opt_state { OPT_UNSET, OPT_DEFAULT } to replace slen = -1 for tracking option state - Replace all slen = -1 / slen != -1 checks with state = OPT_UNSET / state != OPT_UNSET - Set OPT_DEFAULT for options initialised in dhcp_init() and at reply time --- dhcp.c | 58 ++++++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 38 insertions(+), 20 deletions(-)

Reviewed-by: Laurent Vivier one comment below

diff --git a/dhcp.c b/dhcp.c index bb72b72..321968a 100644 --- a/dhcp.c +++ b/dhcp.c @@ -33,13 +33,24 @@ #include "log.h" #include "dhcp.h"

+/** + * enum opt_state - DHCP option state + * @OPT_UNSET: Option not configured + * @OPT_DEFAULT: Option derived from host configuration + */ +enum opt_state { + OPT_UNSET = 0, + OPT_DEFAULT, +}; + /** * struct opt - DHCP option * @sent: Convenience flag, set while filling replies - * @slen: Length of option defined for server, -1 if not going to be sent + * @slen: Length of option defined for server * @s: Option payload from server * @clen: Length of option received from client, -1 if not received * @c: Option payload from client + * @state: Option state (unset or default) */ struct opt { int sent; @@ -47,6 +58,7 @@ struct opt { uint8_t s[255]; int clen; uint8_t c[255]; + enum opt_state state; };

static struct opt opts[256]; @@ -73,19 +85,17 @@ static struct opt opts[256]; */ void dhcp_init(void) { - int i; - - for (i = 0; i < ARRAY_SIZE(opts); i++) - opts[i].slen = -1; - - opts[1] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, }; /* Mask */ - opts[3] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, }; /* Router */ - opts[51] = (struct opt) { 0, 4, { 0xff, - 0xff, - 0xff, - 0xff }, 0, { 0 }, }; /* Lease time */ - opts[53] = (struct opt) { 0, 1, { 0 }, 0, { 0 }, }; /* Type */ - opts[54] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, }; /* Server ID */ + /* Mask */ + opts[1] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, OPT_DEFAULT, }; + /* Router */ + opts[3] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, OPT_DEFAULT, }; + /* Lease time */ + opts[51] = (struct opt) { 0, 4, { 0xff, 0xff, 0xff, 0xff }, + 0, { 0 }, OPT_DEFAULT }; + /* Type */ + opts[53] = (struct opt) { 0, 1, { 0 }, 0, { 0 }, OPT_DEFAULT, }; + /* Server ID */ + opts[54] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, OPT_DEFAULT, };

unneeded comma after OPT_DEFAULT

}

/** @@ -183,13 +193,13 @@ static int fill(struct msg *m)

for (i = 0; i < opts[55].clen; i++) { o = opts[55].c[i]; - if (opts[o].slen != -1) + if (opts[o].state != OPT_UNSET) if (fill_one(m->o, OPT_MAX, o, &offset)) debug("DHCP: skipping option %i", o); }

for (o = 0; o < 255; o++) { - if (opts[o].slen != -1 && !opts[o].sent) + if (opts[o].state != OPT_UNSET && !opts[o].sent) if (fill_one(m->o, OPT_MAX, o, &offset)) debug("DHCP: skipping option %i", o); } @@ -243,6 +253,7 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len) int i;

opts[119].slen = 0; + opts[119].state = OPT_DEFAULT;

for (i = 0; i < 255; i++) max_len -= opts[i].slen; @@ -291,7 +302,7 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len) }

if (!opts[119].slen) - opts[119].slen = -1; + opts[119].state = OPT_UNSET; }

/** @@ -389,7 +400,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data) iov_drop_header(data, *olen); }

- opts[80].slen = -1; + opts[80].state = OPT_UNSET; if (opts[53].clen > 0 && opts[53].c[0] == DHCPDISCOVER) { if (opts[80].clen == -1) { info("DHCP: offer to discover"); @@ -398,6 +409,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data) info("DHCP: ack to discover (Rapid Commit)"); opts[53].s[0] = DHCPACK; opts[80].slen = 0; + opts[80].state = OPT_DEFAULT; } } else if (opts[53].clen <= 0 || opts[53].c[0] == DHCPREQUEST) { info("%s: ack to request", /* DHCP needs a valid message type */ @@ -421,6 +433,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data) != (c->ip4.guest_gw.s_addr & mask.s_addr)) { /* a.b.c.d/32:0.0.0.0, 0:a.b.c.d */ opts[121].slen = 14; + opts[121].state = OPT_DEFAULT; opts[121].s[0] = 32; memcpy(opts[121].s + 1, &c->ip4.guest_gw, sizeof(c->ip4.guest_gw)); @@ -430,6 +443,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)

if (c->mtu) { opts[26].slen = 2; + opts[26].state = OPT_DEFAULT; opts[26].s[0] = c->mtu / 256; opts[26].s[1] = c->mtu % 256; } @@ -441,12 +455,15 @@ int dhcp(const struct ctx *c, struct iov_tail *data) ((struct in_addr *)opts[6].s)[i] = c->ip4.dns[i]; opts[6].slen += sizeof(uint32_t); } - if (!opts[6].slen) - opts[6].slen = -1; + if (opts[6].slen) + opts[6].state = OPT_DEFAULT; + else + opts[6].state = OPT_UNSET;

opt_len = strlen(c->hostname); if (opt_len > 0) { opts[12].slen = opt_len; + opts[12].state = OPT_DEFAULT; memcpy(opts[12].s, &c->hostname, opt_len); }

@@ -463,6 +480,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data) encode_domain_name((char *)opts[81].s + 3, c->fqdn);

opts[81].slen = opt_len; + opts[81].state = OPT_DEFAULT; } else { debug("DHCP: client FQDN option doesn't fit, skipping"); }