[PATCH 2/2] dhcp: Add --dhcp-boot option to set boot filename in DHCP replies

[Laurent Vivier <lvivier@redhat.com>]

Add a --dhcp-boot option that populates the 'file' field in DHCP reply
messages with the given filename.

Using --dhcp-boot together with --no-dhcp is rejected at startup.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 conf.c  | 10 ++++++++++
 dhcp.c  |  5 ++++-
 passt.1 |  6 ++++++
 passt.h |  1 +
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/conf.c b/conf.c
index ae37bf96dac4..2cf1bc7420d3 100644
--- a/conf.c
+++ b/conf.c
@@ -984,6 +984,7 @@ static void usage(const char *name, FILE *f, int status)
 		"  --no-udp		Disable UDP protocol handler\n"
 		"  --no-icmp		Disable ICMP/ICMPv6 protocol handler\n"
 		"  --no-dhcp		Disable DHCP server\n"
+		"  --dhcp-boot FILE	DHCP boot filename option\n"
 		"  --no-ndp		Disable NDP responses\n"
 		"  --no-dhcpv6		Disable DHCPv6 server\n"
 		"  --no-ra		Disable router advertisements\n"
@@ -1537,6 +1538,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		{"migrate-exit", no_argument,		NULL,		29 },
 		{"migrate-no-linger", no_argument,	NULL,		30 },
 		{"stats", required_argument,		NULL,		31 },
+		{"dhcp-boot", required_argument,	NULL,		32 },
 		{ 0 },
 	};
 	const char *optstring = "+dqfel:hs:F:I:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:T:U:";
@@ -1775,6 +1777,11 @@ void conf(struct ctx *c, int argc, char **argv)
 				die("Can't display statistics if not running in foreground");
 			c->stats = strtol(optarg, NULL, 0);
 			break;
+		case 32:
+			if (snprintf_check(c->dhcp_boot, sizeof(c->dhcp_boot),
+					   "%s", optarg))
+				die("Invalid DHCP bootfile name: %s", optarg);
+			break;
 		case 'd':
 			c->debug = 1;
 			c->quiet = 0;
@@ -2206,6 +2213,9 @@ void conf(struct ctx *c, int argc, char **argv)
 		c->no_dhcpv6 = 1;
 	}
 
+	if (c->no_dhcp && c->dhcp_boot[0])
+		die("--dhcp-boot cannot be used with --no-dhcp");
+
 	get_dns(c);
 
 	if (!*c->pasta_ifn) {
diff --git a/dhcp.c b/dhcp.c
index 1ff8cba9f93d..7fdb6e051dec 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -344,6 +344,9 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	    m->op != BOOTREQUEST)
 		return -1;
 
+	static_assert(sizeof(reply.file) == sizeof(c->dhcp_boot),
+		      "dhcp_boot must have the same size as reply.file");
+
 	reply.op		= BOOTREPLY;
 	reply.htype		= m->htype;
 	reply.hlen		= m->hlen;
@@ -357,7 +360,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	reply.giaddr		= m->giaddr;
 	memcpy(&reply.chaddr,	m->chaddr,	sizeof(reply.chaddr));
 	memset(&reply.sname,	0,		sizeof(reply.sname));
-	memset(&reply.file,	0,		sizeof(reply.file));
+	memcpy(&reply.file,	c->dhcp_boot,	sizeof(reply.file));
 	reply.magic		= m->magic;
 
 	for (i = 0; i < ARRAY_SIZE(opts); i++)
diff --git a/passt.1 b/passt.1
index 13e8df9de9f3..a6ac2884bf3f 100644
--- a/passt.1
+++ b/passt.1
@@ -342,6 +342,12 @@ Disable the DHCP server. DHCP client requests coming from guest or target
 namespace will be silently dropped. Implied if there is no gateway on the
 selected IPv4 default route.
 
+.TP
+.BR \-\-dhcp-boot " " \fIfile
+Set the boot filename in DHCP replies to \fIfile\fR. This populates the
+\fIfile\fR field in BOOTP/DHCP reply messages, which can be used for
+network booting (PXE). Cannot be used with \fB--no-dhcp\fR.
+
 .TP
 .BR \-\-no-ndp
 Disable Neighbor Discovery. NDP messages coming from guest or target
diff --git a/passt.h b/passt.h
index 62b8dcdf0a41..4044a4c07ea3 100644
--- a/passt.h
+++ b/passt.h
@@ -255,6 +255,7 @@ struct ctx {
 
 	char hostname[PASST_MAXDNAME];
 	char fqdn[PASST_MAXDNAME];
+	char dhcp_boot[128];
 
 	int ifi6;
 	struct ip6_ctx ip6;
-- 
2.53.0