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

DHCP options block from the contents.

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;
+}