Re: [PATCH v7 4/7] dhcp: Add --dhcp-boot command-line option

[Stefano Brivio <sbrivio@redhat.com>]

On Thu,  1 Oct 2026 18:45:57 +0530
Anshu Kumari <anskuma@redhat.com> wrote:

> Add a convenience shorthand --dhcp-boot FILE that sets the boot
> file name (DHCP option 67) for network boot.  This is equivalent
> to --dhcp-opt 67,FILE.
> 
> Per RFC 2132, Section 9.5, the boot file name is placed in the
> 'file' header field of the DHCP reply.
> 
> Link: https://bugs.passt.top/show_bug.cgi?id=192
> Signed-off-by: Anshu Kumari <anskuma@redhat.com>
> ---
> v7:
>   - moved ```has_bootfile``` declaration and initialization in
>     this patch.
> 
> v6:
>   - no changes.
> 
> v5:
>   - replaced conf_dhcp_option() to dhcp_set_opt().
> 
> v4:
>   - Changed argument name from URL to FILE in usage and man page.
>   - Fixed UEFI HTTP boot wording in man page
> 
> v3:
>   - case 32 now calls dhcp_add_option(c, 67, optarg).
>   - Handles duplicate codes: --dhcp-boot and --dhcp-opt 67 coexist
>     correctly, last value wins.
> 
> v2:
>   - Removed separate dhcp_boot[PATH_MAX] field — --dhcp-boot foo
>     now stores into custom_opts[] as code 67 (same as --dhcp-opt 67,foo)
> ---
>  conf.c  |  5 +++++
>  dhcp.c  | 10 ++++++++++
>  passt.1 |  7 +++++++
>  3 files changed, 22 insertions(+)
> 
> diff --git a/conf.c b/conf.c
> index c12a9335..37720bb5 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -634,6 +634,7 @@ static void usage(const char *name, FILE *f, int status)
>  		"    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"
> +		"  --dhcp-boot FILE	Boot file name for network boot\n"
>  		"  --dhcp-opt CODE,VAL	Set DHCP option CODE to VAL\n");
>  	if (strstr(name, "pasta"))
>  		FPRINTF(f, "    default: don't use any search list\n");
> @@ -1354,6 +1355,7 @@ void conf(struct ctx *c, int argc, char **argv)
>  		{"stats", required_argument,		NULL,		31 },
>  		{"conf-path",	required_argument,	NULL,		'c' },
>  		{"chroot-fallback", no_argument,	NULL, 		32 },
> +		{"dhcp-boot", required_argument,	NULL,		33 },
>  		{"dhcp-opt", required_argument,		NULL,		34 },
>  		{ 0 },
>  	};
> @@ -1596,6 +1598,9 @@ void conf(struct ctx *c, int argc, char **argv)
>  		case 32:
>  			c->chroot_fallback = true;
>  			break;
> +		case 33:
> +			dhcp_set_opt(67, optarg);
> +			break;
>  		case 34: {
>  			unsigned long optcode;
>  
> diff --git a/dhcp.c b/dhcp.c
> index dd3ab6c6..4dccae7b 100644
> --- a/dhcp.c
> +++ b/dhcp.c
> @@ -600,6 +600,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
>  	const struct udphdr *uh;
>  	struct msg m_storage;
>  	struct msg const *m;
> +	bool has_bootfile;
>  	struct msg reply;
>  	unsigned int i;
>  
> @@ -772,8 +773,17 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
>  	if (!c->no_dhcp_dns_search)
>  		opt_set_dns_search(c, sizeof(m->o));
>  
> +	/* RFC 2132, Section 9.5: put boot file name in the 'file' header
> +	 * field.
> +	 */
> +	has_bootfile = opts[67].slen > 0 &&
> +		       (size_t)opts[67].slen < sizeof(reply.file);
> +
>  	dlen = offsetof(struct msg, o) + fill(&reply);
>  
> +	if (has_bootfile)
> +		memcpy(reply.file, opts[67].s, opts[67].slen);
> +
>  	if (m->flags & FLAG_BROADCAST)
>  		dst = in4addr_broadcast;
>  	else
> diff --git a/passt.1 b/passt.1
> index 2bfe7d50..fdbe3d2c 100644
> --- a/passt.1
> +++ b/passt.1
> @@ -440,6 +440,13 @@ Send \fIname\fR as DHCP option 12 (hostname).
>  FQDN to configure the client with.
>  Send \fIname\fR as Client FQDN: DHCP option 81 and DHCPv6 option 39.
>  
> +.TP
> +.BR \-\-dhcp-boot " " \fIfile

Given that options in conf() need to be renumbered anyway because of
the merge conflict, what about moving this after --dhcp-opt in the
documentation (it refers to it and it's a special case of it, so it
would look more natural to have it afterwards) and then make ordering
consistent in conf() and usage message?

> +Convenience shorthand for \fB\-\-dhcp-opt\fR 67,\fIfile\fR.
> +Sets the boot file name (DHCP option 67) for network boot.
> +For UEFI HTTP boot, the vendor class identifier also needs to be set using
> +\fB\-\-dhcp-opt\fR 60,HTTPClient.
> +
>  .TP
>  .BR \-\-dhcp-opt " " \fICODE\fR,\fIVALUE\fR
>  Set DHCP option \fICODE\fR (1\-254) to \fIVALUE\fR. The value format depends

-- 
Stefano