Add (untested) code for parsing a received DHCP packet and constructing a

DHCP options block from the contents.

src/include/gpxe/dhcp.h

@@ -9,6 +9,87 @@
 
 #include <stdint.h>
 #include <gpxe/list.h>
+#include <gpxe/in.h>
+
+/**
+ * A DHCP packet
+ *
+ */
+struct dhcp_packet {
+	/** Operation
+	 *
+	 * This must be either @c BOOTP_REQUEST or @c BOOTP_REPLY.
+	 */
+	uint8_t op;
+	/** Hardware address type
+	 *
+	 * This is an ARPHRD_XXX constant.
+	 */
+	uint8_t htype;
+	/** Hardware address length */
+	uint8_t hlen;
+	/** Number of hops from server */
+	uint8_t hops;
+	/** Transaction ID */
+	uint32_t xid;
+	/** Seconds since start of acquisition */
+	uint16_t secs;
+	/** Flags */
+	uint16_t flags;
+	/** "Client" IP address
+	 *
+	 * This is filled in if the client already has an IP address
+	 * assigned and can respond to ARP requests.
+	 */
+	struct in_addr ciaddr;
+	/** "Your" IP address
+	 *
+	 * This is the IP address assigned by the server to the client.
+	 */
+	struct in_addr yiaddr;
+	/** "Server" IP address
+	 *
+	 * This is the IP address of the next server to be used in the
+	 * boot process.
+	 */
+	struct in_addr siaddr;
+	/** "Gateway" IP address
+	 *
+	 * This is the IP address of the DHCP relay agent, if any.
+	 */
+	struct in_addr giaddr;
+	/** Client hardware address */
+	uint8_t chaddr[16];
+	/** Server host name (null terminated)
+	 *
+	 * This field may be overridden and contain DHCP options
+	 */
+	uint8_t sname[64];
+	/** Boot file name (null terminated)
+	 *
+	 * This field may be overridden and contain DHCP options
+	 */
+	uint8_t file[128];
+	/** DHCP magic cookie
+	 *
+	 * Must have the value @c DHCP_MAGIC_COOKIE.
+	 */
+	uint32_t magic;
+	/** DHCP options
+	 *
+	 * Variable length; extends to the end of the packet.
+	 */
+	uint8_t options[0];
+};
+
+/** Opcode for a request from client to server */
+#define BOOTP_REQUEST 1
+
+/** Opcode for a reply from server to client */
+#define BOOTP_REPLY 2
+
+/** DHCP magic cookie */
+#define DHCP_MAGIC_COOKIE 0x63825363UL
 
 /** Construct a tag value for an encapsulated option
  *
@@ -22,7 +103,7 @@
 #define DHCP_ENCAPSULATOR( encap_opt ) ( (encap_opt) >> 8 )
 /** Extract encapsulated option tag from encapsulated tag value */
 #define DHCP_ENCAPSULATED( encap_opt ) ( (encap_opt) & 0xff )
-
+/** Option is encapsulated */
 #define DHCP_IS_ENCAP_OPT( opt ) DHCP_ENCAPSULATOR( opt )
 
 /**
@@ -30,13 +111,80 @@
  * @{
  */
 
+/** Padding
+ *
+ * This tag does not have a length field; it is always only a single
+ * byte in length.
+ */
 #define DHCP_PAD 0
-#define DHCP_END 255
 
+/** Option overloading
+ *
+ * The value of this option is the bitwise-OR of zero or more
+ * DHCP_OPTION_OVERLOAD_XXX constants.
+ */
+#define DHCP_OPTION_OVERLOAD 52
+
+/** The "file" field is overloaded to contain extra DHCP options */
+#define DHCP_OPTION_OVERLOAD_FILE 1
+
+/** The "sname" field is overloaded to contain extra DHCP options */
+#define DHCP_OPTION_OVERLOAD_SNAME 2
+
+/** TFTP server name
+ *
+ * This option replaces the fixed "sname" field, when that field is
+ * used to contain overloaded options.
+ */
+#define DHCP_TFTP_SERVER_NAME 66
+
+/** Bootfile name
+ *
+ * This option replaces the fixed "file" field, when that field is
+ * used to contain overloaded options.
+ */
+#define DHCP_BOOTFILE_NAME 67
+
+/** Etherboot-specific encapsulated options
+ *
+ * This encapsulated options field is used to contain all options
+ * specific to Etherboot (i.e. not assigned by IANA or other standards
+ * bodies).
+ */
 #define DHCP_EB_ENCAP 175
 
+/** Priority of this options block
+ *
+ * This is a signed 8-bit integer field indicating the priority of
+ * this block of options.  It can be used to specify the relative
+ * priority of multiple option blocks (e.g. options from non-volatile
+ * storage versus options from a DHCP server).
+ */
 #define DHCP_EB_PRIORITY DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 1 )
 
+/** "Your" IP address
+ *
+ * This option is used internally to contain the value of the "yiaddr"
+ * field, in order to provide a consistent approach to storing and
+ * processing options.  It should never be present in a DHCP packet.
+ */
+#define DHCP_EB_YIADDR DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 2 )
+
+/** "Server" IP address
+ *
+ * This option is used internally to contain the value of the "siaddr"
+ * field, in order to provide a consistent approach to storing and
+ * processing options.  It should never be present in a DHCP packet.
+ */
+#define DHCP_EB_SIADDR DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 3 )
+
+/** End of options
+ *
+ * This tag does not have a length field; it is always only a single
+ * byte in length.
+ */
+#define DHCP_END 255
+
 /** @} */
 
 /**
@@ -118,7 +266,6 @@ extern struct dhcp_option *
 set_dhcp_option ( struct dhcp_option_block *options, unsigned int tag,
 		  const void *data, size_t len );
 
-
 /**
  * Find DHCP numerical option, and return its value
  *

src/net/udp/dhcp.c

@@ -0,0 +1,172 @@
+/*
+ * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <string.h>
+#include <assert.h>
+#include <byteswap.h>
+#include <gpxe/netdevice.h>
+#include <gpxe/dhcp.h>
+
+/** @file
+ *
+ * Dynamic Host Configuration Protocol
+ *
+ */
+
+/**
+ * Calculate used length of a field containing DHCP options
+ *
+ * @v data		Field containing DHCP options
+ * @v max_len		Field length
+ * @ret len		Used length (excluding the @c DHCP_END tag)
+ */
+static size_t dhcp_field_len ( const void *data, size_t max_len ) {
+	struct dhcp_option_block options;
+	struct dhcp_option *end;
+
+	options.data = ( ( void * ) data );
+	options.len = max_len;
+	end = find_dhcp_option ( &options, DHCP_END );
+	return ( end ? ( ( ( void * ) end ) - data ) : 0 );
+}
+
+/**
+ * Merge field containing DHCP options or string into DHCP options block
+ *
+ * @v options		DHCP option block
+ * @v data		Field containing DHCP options
+ * @v max_len		Field length
+ * @v tag		DHCP option tag, or 0
+ *
+ * If @c tag is non-zero, the field will be treated as a
+ * NUL-terminated string representing the value of the specified DHCP
+ * option.  If @c tag is zero, the field will be treated as a block of
+ * DHCP options, and simply appended to the existing options in the
+ * option block.
+ *
+ * The caller must ensure that there is enough space in the options
+ * block to perform the merge.
+ */
+static void merge_dhcp_field ( struct dhcp_option_block *options,
+			       const void *data, size_t max_len,
+			       unsigned int tag ) {
+	size_t len;
+	void *dest;
+	struct dhcp_option *end;
+
+	if ( tag ) {
+		set_dhcp_option ( options, tag, data, strlen ( data ) );
+	} else {
+		len = dhcp_field_len ( data, max_len );
+		dest = ( options->data + options->len - 1 );
+		memcpy ( dest, data, len );
+		options->len += len;
+		end = ( dest + len );
+		end->tag = DHCP_END;
+	}
+}
+
+/**
+ * Parse DHCP packet and construct DHCP options block
+ *
+ * @v data		DHCP packet
+ * @v len		Length of DHCP packet
+ * @ret options		DHCP options block, or NULL
+ *
+ * Parses a received DHCP packet and canonicalises its contents into a
+ * single DHCP options block.  The "file" and "sname" fields are
+ * converted into the corresponding DHCP options (@c
+ * DHCP_BOOTFILE_NAME and @c DHCP_TFTP_SERVER_NAME respectively).  If
+ * these fields are used for option overloading, their options are
+ * merged in to the options block.  The values of the "yiaddr" and
+ * "siaddr" fields will be stored within the options block as the
+ * options @c DHCP_EB_YIADDR and @c DHCP_EB_SIADDR.
+ * 
+ * Note that this call allocates new memory for the constructed DHCP
+ * options block; it is the responsibility of the caller to eventually
+ * free this memory.
+ */
+struct dhcp_option_block * dhcp_parse ( const void *data, size_t len ) {
+	const struct dhcp_packet *dhcppkt = data;
+	struct dhcp_option_block *options;
+	size_t options_len;
+	unsigned int overloading;
+
+	/* Calculate size of resulting concatenated option block:
+	 *
+	 *   The "options" field : length of the field minus the DHCP_END tag.
+	 *
+	 *   The "file" field : maximum length of the field minus the
+	 *   NUL terminator, plus a 2-byte DHCP header or, if used for
+	 *   option overloading, the length of the field minus the
+	 *   DHCP_END tag.
+	 *
+	 *   The "sname" field : as for the "file" field.
+	 *
+	 *   15 bytes for an encapsulated options field to contain the
+	 *   value of the "yiaddr" and "siaddr" fields
+	 *
+	 *   1 byte for a final terminating DHCP_END tag.
+	 */
+	options_len = ( ( len - offsetof ( typeof ( *dhcppkt ), options ) ) - 1
+			+ ( sizeof ( dhcppkt->file ) + 1 )
+			+ ( sizeof ( dhcppkt->sname ) + 1 )
+			+ 15 /* yiaddr and siaddr */
+			+ 1 /* DHCP_END tag */ );
+	
+	/* Allocate empty options block of required size */
+	options = alloc_dhcp_options ( options_len );
+	if ( ! options ) {
+		DBG ( "DHCP could not allocate %d-byte option block\n",
+		      options_len );
+		return NULL;
+	}
+	
+	/* Merge in "options" field, if this is a DHCP packet */
+	if ( dhcppkt->magic == htonl ( DHCP_MAGIC_COOKIE ) ) {
+		merge_dhcp_field ( options, dhcppkt->options,
+				   ( len -
+				     offsetof ( typeof (*dhcppkt), options ) ),
+				   0 /* Always contains options */ );
+	}
+
+	/* Identify overloaded fields */
+	overloading = find_dhcp_num_option ( options, DHCP_OPTION_OVERLOAD );
+	
+	/* Merge in "file" and "sname" fields */
+	merge_dhcp_field ( options, dhcppkt->file, sizeof ( dhcppkt->file ),
+			   ( ( overloading & DHCP_OPTION_OVERLOAD_FILE ) ?
+			     DHCP_BOOTFILE_NAME : 0 ) );
+	merge_dhcp_field ( options, dhcppkt->sname, sizeof ( dhcppkt->sname ),
+			   ( ( overloading & DHCP_OPTION_OVERLOAD_SNAME ) ?
+			     DHCP_TFTP_SERVER_NAME : 0 ) );
+
+	/* Set options for "yiaddr" and "siaddr", if present */
+	if ( dhcppkt->yiaddr.s_addr ) {
+		set_dhcp_option ( options, DHCP_EB_YIADDR,
+				  &dhcppkt->yiaddr, sizeof (dhcppkt->yiaddr) );
+	}
+	if ( dhcppkt->siaddr.s_addr ) {
+		set_dhcp_option ( options, DHCP_EB_SIADDR,
+				  &dhcppkt->siaddr, sizeof (dhcppkt->siaddr) );
+	}
+	
+	assert ( options->len <= options->max_len );
+
+	return options;
+}