On Fri, Jul 17, 2026 at 11:26:44PM +0530, Anshu Kumari wrote:
> Mark Client FQDN (option 81) as concatenation-requiring per
> RFC 4702, Section 2.  When the encoded FQDN exceeds 255 bytes,
> fill() now splits it across DHCP message fields using the RFC 3396
> splitting infrastructure instead of silently dropping it.
> 
> Link: https://bugs.passt.top/show_bug.cgi?id=192
> Signed-off-by: Anshu Kumari <anskuma@redhat.com>
> ---
> v5:
>   - New patch: mark Client FQDN (option 81) as concatenation-requiring per RFC 4702
> ---
>  dhcp.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/dhcp.c b/dhcp.c
> index 6bebb5f..a54ac58 100644
> --- a/dhcp.c
> +++ b/dhcp.c
> @@ -484,9 +484,15 @@ enum dhcp_overload {
>   */
>  static bool is_concat_opt(int o)
>  {
> -	if ((size_t)o >= ARRAY_SIZE(dhcp_opt_types))
> -		return false;
> -	return dhcp_opt_types[o] == DHCP_OPT_STR_CONCAT;
> +	if ((size_t)o < ARRAY_SIZE(dhcp_opt_types) &&
> +	    dhcp_opt_types[o] == DHCP_OPT_STR_CONCAT)
> +		return true;
> +
> +	/* RFC 4702, Section 2: Client FQDN option requires concatenation */
> +	if (o == 81)
> +		return true;

Why is this explicitly special cased, rather than setting the type in
the table?  Come to that, does this do anything, since we don't
appear to currently allow option 81 anyway.

> +
> +	return false;
>  }
>  
>  /**
> -- 
> 2.54.0
> 

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