Re: [PATCH v2] dhcpv6: support rapid commit dhcp6 option

[Jerome Forissier <jerome.forissier@arm.com>]

Hi Yuxiao,

On 25/08/2026 19:53, Yuxiao Zhang wrote:
> Support rapid commit option code 14 which bypass the advertise and
> request state. The option is enabled by DHCP6_RAPID_COMMIT.
> 
> Signed-off-by: Yuxiao Zhang <yuxiaozhang@google.com>
> ---
> 
> Changes in v2:
> - Reject rapid commit option if option_len != 0
> - Drop redundant NULL check on dhcp6_hdr
> 
>  cmd/Kconfig  |  8 ++++++++
>  net/dhcpv6.c | 43 ++++++++++++++++++++++++++++++++++++-------
>  net/dhcpv6.h |  2 ++
>  3 files changed, 46 insertions(+), 7 deletions(-)
> 
> diff --git a/cmd/Kconfig b/cmd/Kconfig
> index ff90a87024c..b3cf3a6d8b6 100644
> --- a/cmd/Kconfig
> +++ b/cmd/Kconfig
> @@ -1996,6 +1996,14 @@ config DHCP6_ENTERPRISE_ID
>  	int "Enterprise ID to send in DHCPv6 Vendor Class Option"
>  	default 0
>  
> +config DHCP6_RAPID_COMMIT
> +	bool "Request Rapid Commit (2-message exchange) from DHCPv6 server"
> +	default n
> +	help
> +	  Request the Rapid Commit option (option 14) in DHCPv6 Solicit
> +	  messages to enable a 2-message exchange (Solicit-Reply) rather
> +	  than the default 4-message exchange.
> +
>  endif
>  
>  config BOOTP_MAY_FAIL
> diff --git a/net/dhcpv6.c b/net/dhcpv6.c
> index 640f089a2e1..5ed8449edb5 100644
> --- a/net/dhcpv6.c
> +++ b/net/dhcpv6.c
> @@ -115,6 +115,9 @@ static int dhcp6_add_option(int option_id, uchar *pkt)
>  
>  		opt_len = sizeof(struct dhcp6_option_ia_na);
>  		break;
> +	case DHCP6_OPTION_RAPID_COMMIT:
> +		opt_len = 0;
> +		break;
>  	case DHCP6_OPTION_ORO:
>  		oro_opt = (struct dhcp6_option_oro *)dhcp_option_start;
>  		oro_opt->req_option_code[num_oro++] = htons(DHCP6_OPTION_OPT_BOOTFILE_URL);
> @@ -194,6 +197,8 @@ static void dhcp6_send_solicit_packet(void)
>  	pkt += dhcp6_add_option(DHCP6_OPTION_ELAPSED_TIME, pkt);
>  	pkt += dhcp6_add_option(DHCP6_OPTION_IA_NA, pkt);
>  	pkt += dhcp6_add_option(DHCP6_OPTION_ORO, pkt);
> +	if (IS_ENABLED(CONFIG_DHCP6_RAPID_COMMIT))
> +		pkt += dhcp6_add_option(DHCP6_OPTION_RAPID_COMMIT, pkt);
>  	if (CONFIG_DHCP_PXE_CLIENTARCH != 0xFF)
>  		pkt += dhcp6_add_option(DHCP6_OPTION_CLIENT_ARCH_TYPE, pkt);
>  	pkt += dhcp6_add_option(DHCP6_OPTION_VENDOR_CLASS, pkt);
> @@ -448,6 +453,16 @@ static void dhcp6_parse_options(uchar *rx_pkt, unsigned int len)
>  			}
>  			sm_params.rx_status.preference = *option_ptr;
>  			break;
> +		case DHCP6_OPTION_RAPID_COMMIT:
> +			if (option_len != 0) {
> +				debug("Invalid rapid commit option length\n");
> +				break;
> +			}
> +			if (IS_ENABLED(CONFIG_DHCP6_RAPID_COMMIT)) {
> +				debug("DHCP6_OPTION_RAPID_COMMIT FOUND\n");
> +				sm_params.rx_status.rapid_commit_found = true;
> +			}
> +			break;
>  		default:
>  			debug("Unknown Option ID: %d, skipping parsing\n",
>  			      ntohs(option_hdr->option_id));
> @@ -618,14 +633,28 @@ static void dhcp6_state_machine(bool timeout, uchar *rx_pkt, unsigned int len)
>  		break;
>  	case DHCP6_SOLICIT:
>  		if (!timeout) {
> -			/* check the rx packet and determine if we can transition to next
> -			 * state.
> -			 */
> -			if (dhcp6_check_advertise_packet(rx_pkt, len))
> -				return;
> +			struct dhcp6_hdr *dhcp6_hdr = (struct dhcp6_hdr *)rx_pkt;
> +
> +			if (IS_ENABLED(CONFIG_DHCP6_RAPID_COMMIT) &&
> +			    dhcp6_hdr->msg_type == DHCP6_MSG_REPLY) {
> +				if (dhcp6_check_reply_packet(rx_pkt, len))
> +					return;
> +				if (!sm_params.rx_status.rapid_commit_found) {
> +					debug("[DHCPv6] REPLY received without Rapid Commit option, ignoring\n");
> +					return;
> +				}

dhcp6_check_reply_packet() calls dhcp6_parse_options(), which has side
effects such as updating the bootfile information. I think the Rapid Commit check
needs to happen before applying the other reply options.

> +				debug("REPLY (Rapid Commit) good, transition to DONE\n");
> +				sm_params.next_state = DHCP6_DONE;
> +			} else {
> +				/* check the rx packet and determine if we can transition to next
> +				 * state.
> +				 */
> +				if (dhcp6_check_advertise_packet(rx_pkt, len))
> +					return;
>  
> -			debug("ADVERTISE good, transition to REQUEST\n");
> -			sm_params.next_state = DHCP6_REQUEST;
> +				debug("ADVERTISE good, transition to REQUEST\n");
> +				sm_params.next_state = DHCP6_REQUEST;
> +			}
>  		} else if (sm_params.retry_cnt == 1)  {
>  			/* If a server UID was received in the first SOLICIT period
>  			 * transition to REQUEST
> diff --git a/net/dhcpv6.h b/net/dhcpv6.h
> index d41a3c30615..49f20390730 100644
> --- a/net/dhcpv6.h
> +++ b/net/dhcpv6.h
> @@ -24,6 +24,7 @@
>  #define DHCP6_OPTION_PREFERENCE		7
>  #define DHCP6_OPTION_ELAPSED_TIME	8
>  #define DHCP6_OPTION_STATUS_CODE	13
> +#define DHCP6_OPTION_RAPID_COMMIT	14
>  #define DHCP6_OPTION_OPT_BOOTFILE_URL	59
>  #define DHCP6_OPTION_OPT_BOOTFILE_PARAM	60
>  #define DHCP6_OPTION_SOL_MAX_RT		82
> @@ -152,6 +153,7 @@ struct dhcp6_rx_pkt_status {
>  	enum dhcp6_status	ia_status_code;
>  	enum dhcp6_status	status_code;
>  	u8			preference;
> +	bool			rapid_commit_found;
>  };
>  
>  /**
> ---
> base-commit: 527115ef6783cec49e5610c523c124b399011361
> branch: main
> 

Thanks,
-- 
Jerome