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

[Anshu Kumari <anskuma@redhat.com>]

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
+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
-- 
2.55.0