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

On Thu, 1 Oct 2026 18:45:57 +0530 Anshu Kumari 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 --- 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