[PATCH] net: dhcp: allow to set transmitted vendor id

[Enrico Scholz]

For net boot setups it is useful to submit boot params like server or
bootfile over dhcp.  To distinguish barebox from e.g. pxe machines, a
custom vendor id can be sent in dhcp discover/request messages.

E.g. the ISC dhcp server can be configured with

| if substring(option vendor-class-identifier,0,8) = "barebox:" {
| 	next-server		192.168.3.24;
| 	server-name		"192.168.3.24";
| 	option tftp-server-name	"192.168.3.24";
| 	option root-path = concat("/srv/sysroots/by-mac/",
|          binary-to-ascii (16, 8, "-", substring (hardware, 1, 6)));
| }

to sent boot params which are valid for barebox hosts only.

Signed-off-by: Enrico Scholz <enrico.scholz at sigma-chemnitz.de>
---
 net/Kconfig |   13 +++++++++++++
 net/dhcp.c  |   12 ++++++++++++
 2 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/net/Kconfig b/net/Kconfig
index 3169d20..56d6ee8 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -7,6 +7,19 @@ config NET_DHCP
 	bool
 	prompt "dhcp support"
 
+config NET_DHCP_VENDOR_ID
+        string
+	prompt "dhcp vendor id"
+	depends on NET_DHCP
+	default "barebox:default"
+	help
+	  DHCP Vendor ID (code 60) submitted in DHCP requests. It can
+	  be used in the DHCP server's configuration to select options
+	  (e.g. bootfile or server) which are valid for barebox clients
+	  only.
+
+	  An empty string will suppress generation of such requests.
+
 config NET_NFS
 	bool
 	prompt "nfs support"
diff --git a/net/dhcp.c b/net/dhcp.c
index 2ce9090..65f2614 100644
--- a/net/dhcp.c
+++ b/net/dhcp.c
@@ -129,6 +129,7 @@ static void bootp_copy_net_params(struct bootp *bp)
  */
 static int dhcp_extended (u8 *e, int message_type, IPaddr_t ServerID, IPaddr_t RequestedIP)
 {
+	size_t vendor_id_len = sizeof CONFIG_NET_DHCP_VENDOR_ID - 1;
 	u8 *start = e;
 	u8 *cnt;
 
@@ -168,6 +169,17 @@ static int dhcp_extended (u8 *e, int message_type, IPaddr_t ServerID, IPaddr_t R
 		*e++ = tmp & 0xff;
 	}
 
+	/* 64 is some arbitrary value to prevent generation of too
+	 * large dhcp requests. */
+	BUILD_BUG_ON(sizeof CONFIG_NET_DHCP_VENDOR_ID > 64);
+
+	if (vendor_id_len > 0) {
+		*e++ = 60;
+		*e++ = vendor_id_len;
+		memcpy(e, CONFIG_NET_DHCP_VENDOR_ID,  vendor_id_len);
+		e   += vendor_id_len;
+	}
+
 	*e++ = 55;		/* Parameter Request List */
 	 cnt = e++;		/* Pointer to count of requested items */
 	*cnt = 0;
-- 
1.7.7.6