text: /*
   * Copyright (C) 2008 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., 51 Franklin Street, Fifth Floor, Boston, MA
   * 02110-1301, USA.
   *
   * You can also choose to distribute this program under the terms of
   * the Unmodified Binary Distribution Licence (as given in the file
   * COPYING.UBDL), provided that you have satisfied its requirements.
   */
  
  FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  
  #include <stdint.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <errno.h>
  #include <string.h>
  #include <ipxe/dhcp.h>
  #include <ipxe/dhcpopts.h>
  
  /** @file
   *
   * DHCP options
   *
   */
  
  /**
   * Obtain printable version of a DHCP option tag
   *
   * @v tag		DHCP option tag
   * @ret name		String representation of the tag
   *
   */
  static inline char * dhcp_tag_name ( unsigned int tag ) {
  	static char name[8];
  
  	if ( DHCP_IS_ENCAP_OPT ( tag ) ) {
  		snprintf ( name, sizeof ( name ), "%d.%d",
  			   DHCP_ENCAPSULATOR ( tag ),
  			   DHCP_ENCAPSULATED ( tag ) );
  	} else {
  		snprintf ( name, sizeof ( name ), "%d", tag );
  	}
  	return name;
  }
  
  /**
   * Get pointer to DHCP option
   *
   * @v options		DHCP options block
   * @v offset		Offset within options block
   * @ret option		DHCP option
   */
  static inline __attribute__ (( always_inline )) struct dhcp_option *
  dhcp_option ( struct dhcp_options *options, unsigned int offset ) {
  	return ( ( struct dhcp_option * ) ( options->data + offset ) );
  }
  
  /**
   * Get offset of a DHCP option
   *
   * @v options		DHCP options block
   * @v option		DHCP option
   * @ret offset		Offset within options block
   */
  static inline __attribute__ (( always_inline )) int
  dhcp_option_offset ( struct dhcp_options *options,
  		     struct dhcp_option *option ) {
  	return ( ( ( void * ) option ) - options->data );
  }
  
  /**
   * Calculate length of any DHCP option
   *
   * @v option		DHCP option
   * @ret len		Length (including tag and length field)
   */
  static unsigned int dhcp_option_len ( struct dhcp_option *option ) {
  	if ( ( option->tag == DHCP_END ) || ( option->tag == DHCP_PAD ) ) {
  		return 1;
  	} else {
  		return ( option->len + DHCP_OPTION_HEADER_LEN );
  	}
  }
  
  /**
   * Find DHCP option within DHCP options block, and its encapsulator (if any)
   *
   * @v options		DHCP options block
   * @v tag		DHCP option tag to search for
   * @ret encap_offset	Offset of encapsulating DHCP option
   * @ret offset		Offset of DHCP option, or negative error
   *
   * Searches for the DHCP option matching the specified tag within the
   * DHCP option block.  Encapsulated options may be searched for by
   * using DHCP_ENCAP_OPT() to construct the tag value.
   *
   * If the option is encapsulated, and @c encap_offset is non-NULL, it
   * will be filled in with the offset of the encapsulating option.
   *
   * This routine is designed to be paranoid.  It does not assume that
   * the option data is well-formatted, and so must guard against flaws
   * such as options missing a @c DHCP_END terminator, or options whose
   * length would take them beyond the end of the data block.
   */
  static int find_dhcp_option_with_encap ( struct dhcp_options *options,
  					 unsigned int tag,
  					 int *encap_offset ) {
  	unsigned int original_tag __attribute__ (( unused )) = tag;
  	struct dhcp_option *option;
  	int offset = 0;
  	ssize_t remaining = options->used_len;
  	unsigned int option_len;
  
  	/* Sanity check */
  	if ( tag == DHCP_PAD )
  		return -ENOENT;
  
  	/* Search for option */
  	while ( remaining ) {
  		/* Calculate length of this option.  Abort processing
  		 * if the length is malformed (i.e. takes us beyond
  		 * the end of the data block).
  		 */
  		option = dhcp_option ( options, offset );
  		option_len = dhcp_option_len ( option );
  		remaining -= option_len;
  		if ( remaining < 0 )
  			break;
  		/* Check for explicit end marker */
  		if ( option->tag == DHCP_END ) {
  			if ( tag == DHCP_END )
  				/* Special case where the caller is interested
  				 * in whether we have this marker or not.
  				 */
  				return offset;
  			else
  				break;
  		}
  		/* Check for matching tag */
  		if ( option->tag == tag ) {
  			DBGC ( options, "DHCPOPT %p found %s (length %d)\n",
  			       options, dhcp_tag_name ( original_tag ),
  			       option_len );
  			return offset;
  		}
  		/* Check for start of matching encapsulation block */
  		if ( DHCP_IS_ENCAP_OPT ( tag ) &&
  		     ( option->tag == DHCP_ENCAPSULATOR ( tag ) ) ) {
  			if ( encap_offset )
  				*encap_offset = offset;
  			/* Continue search within encapsulated option block */
  			tag = DHCP_ENCAPSULATED ( tag );
  			remaining = option_len;
  			offset += DHCP_OPTION_HEADER_LEN;
  			continue;
  		}
  		offset += option_len;
  	}
  
  	return -ENOENT;
  }
  
  /**
   * Refuse to reallocate DHCP option block
   *
   * @v options		DHCP option block
   * @v len		New length
   * @ret rc		Return status code
   */
  int dhcpopt_no_realloc ( struct dhcp_options *options, size_t len ) {
  	return ( ( len <= options->alloc_len ) ? 0 : -ENOSPC );
  }
  
  /**
   * Resize a DHCP option
   *
   * @v options		DHCP option block
   * @v offset		Offset of option to resize
   * @v encap_offset	Offset of encapsulating offset (or -ve for none)
   * @v old_len		Old length (including header)
   * @v new_len		New length (including header)
   * @ret rc		Return status code
   */
  static int resize_dhcp_option ( struct dhcp_options *options,
  				int offset, int encap_offset,
  				size_t old_len, size_t new_len ) {
  	struct dhcp_option *encapsulator;
  	struct dhcp_option *option;
  	ssize_t delta = ( new_len - old_len );
  	size_t old_alloc_len;
  	size_t new_used_len;
  	size_t new_encapsulator_len;
  	void *source;
  	void *dest;
  	int rc;
  
  	/* Check for sufficient space */
  	if ( new_len > DHCP_MAX_LEN ) {
  		DBGC ( options, "DHCPOPT %p overlength option\n", options );
  		return -ENOSPC;
  	}
  	new_used_len = ( options->used_len + delta );
  
  	/* Expand options block, if necessary */
  	if ( new_used_len > options->alloc_len ) {
  		/* Reallocate options block */
  		old_alloc_len = options->alloc_len;
  		if ( ( rc = options->realloc ( options, new_used_len ) ) != 0 ){
  			DBGC ( options, "DHCPOPT %p could not reallocate to "
  			       "%zd bytes\n", options, new_used_len );
  			return rc;
  		}
  		/* Clear newly allocated space */
  		memset ( ( options->data + old_alloc_len ), 0,
  			 ( options->alloc_len - old_alloc_len ) );
  	}
  
  	/* Update encapsulator, if applicable */
  	if ( encap_offset >= 0 ) {
  		encapsulator = dhcp_option ( options, encap_offset );
  		new_encapsulator_len = ( encapsulator->len + delta );
  		if ( new_encapsulator_len > DHCP_MAX_LEN ) {
  			DBGC ( options, "DHCPOPT %p overlength encapsulator\n",
  			       options );
  			return -ENOSPC;
  		}
  		encapsulator->len = new_encapsulator_len;
  	}
  
  	/* Update used length */
  	options->used_len = new_used_len;
  
  	/* Move remainder of option data */
  	option = dhcp_option ( options, offset );
  	source = ( ( ( void * ) option ) + old_len );
  	dest = ( ( ( void * ) option ) + new_len );
  	memmove ( dest, source, ( new_used_len - offset - new_len ) );
  
  	/* Shrink options block, if applicable */
  	if ( new_used_len < options->alloc_len ) {
  		if ( ( rc = options->realloc ( options, new_used_len ) ) != 0 ){
  			DBGC ( options, "DHCPOPT %p could not reallocate to "
  			       "%zd bytes\n", options, new_used_len );
  			return rc;
  		}
  	}
  
  	return 0;
  }
  
  /**
   * Set value of DHCP option
   *
   * @v options		DHCP option block
   * @v tag		DHCP option tag
   * @v data		New value for DHCP option
   * @v len		Length of value, in bytes
   * @ret offset		Offset of DHCP option, or negative error
   *
   * Sets the value of a DHCP option within the options block.  The
   * option may or may not already exist.  Encapsulators will be created
   * (and deleted) as necessary.
   *
   * This call may fail due to insufficient space in the options block.
   * If it does fail, and the option existed previously, the option will
   * be left with its original value.
   */
  static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
  			     const void *data, size_t len ) {
  	static const uint8_t empty_encap[] = { DHCP_END };
  	int offset;
  	int encap_offset = -1;
  	int creation_offset;
  	struct dhcp_option *option;
  	unsigned int encap_tag = DHCP_ENCAPSULATOR ( tag );
  	size_t old_len = 0;
  	size_t new_len = ( len ? ( len + DHCP_OPTION_HEADER_LEN ) : 0 );
  	int rc;
  
  	/* Sanity check */
  	if ( tag == DHCP_PAD )
  		return -ENOTTY;
  
  	creation_offset = find_dhcp_option_with_encap ( options, DHCP_END,
  							NULL );
  	if ( creation_offset < 0 )
  		creation_offset = options->used_len;
  	/* Find old instance of this option, if any */
  	offset = find_dhcp_option_with_encap ( options, tag, &encap_offset );
  	if ( offset >= 0 ) {
  		old_len = dhcp_option_len ( dhcp_option ( options, offset ) );
  		DBGC ( options, "DHCPOPT %p resizing %s from %zd to %zd\n",
  		       options, dhcp_tag_name ( tag ), old_len, new_len );
  	} else {
  		DBGC ( options, "DHCPOPT %p creating %s (length %zd)\n",
  		       options, dhcp_tag_name ( tag ), new_len );
  	}
  
  	/* Ensure that encapsulator exists, if required */
  	if ( encap_tag ) {
  		if ( encap_offset < 0 ) {
  			encap_offset =
  				set_dhcp_option ( options, encap_tag,
  						  empty_encap,
  						  sizeof ( empty_encap ) );
  		}
  		if ( encap_offset < 0 )
  			return encap_offset;
  		creation_offset = ( encap_offset + DHCP_OPTION_HEADER_LEN );
  	}
  
  	/* Create new option if necessary */
  	if ( offset < 0 )
  		offset = creation_offset;
  
  	/* Resize option to fit new data */
  	if ( ( rc = resize_dhcp_option ( options, offset, encap_offset,
  					 old_len, new_len ) ) != 0 )
  		return rc;
  
  	/* Copy new data into option, if applicable */
  	if ( len ) {
  		option = dhcp_option ( options, offset );
  		option->tag = tag;
  		option->len = len;
  		memcpy ( &option->data, data, len );
  	}
  
  	/* Delete encapsulator if there's nothing else left in it */
  	if ( encap_offset >= 0 ) {
  		option = dhcp_option ( options, encap_offset );
  		if ( option->len <= 1 )
  			set_dhcp_option ( options, encap_tag, NULL, 0 );
  	}
  
  	return offset;
  }
  
  /**
   * Check applicability of DHCP option setting
   *
   * @v tag		Setting tag number
   * @ret applies		Setting applies to this option block
   */
  int dhcpopt_applies ( unsigned int tag ) {
  
  	return ( tag && ( tag <= DHCP_ENCAP_OPT ( DHCP_MAX_OPTION,
  						  DHCP_MAX_OPTION ) ) );
  }
  
  /**
   * Store value of DHCP option setting
   *
   * @v options		DHCP option block
   * @v tag		Setting tag number
   * @v data		Setting data, or NULL to clear setting
   * @v len		Length of setting data
   * @ret rc		Return status code
   */
  int dhcpopt_store ( struct dhcp_options *options, unsigned int tag,
  		    const void *data, size_t len ) {
  	int offset;
  
  	offset = set_dhcp_option ( options, tag, data, len );
  	if ( offset < 0 )
  		return offset;
  	return 0;
  }
  
  /**
   * Fetch value of DHCP option setting
   *
   * @v options		DHCP option block
   * @v tag		Setting tag number
   * @v data		Buffer to fill with setting data
   * @v len		Length of buffer
   * @ret len		Length of setting data, or negative error
   */
  int dhcpopt_fetch ( struct dhcp_options *options, unsigned int tag,
  		    void *data, size_t len ) {
  	int offset;
  	struct dhcp_option *option;
  	size_t option_len;
  
  	offset = find_dhcp_option_with_encap ( options, tag, NULL );
  	if ( offset < 0 )
  		return offset;
  
  	option = dhcp_option ( options, offset );
  	option_len = option->len;
  	if ( len > option_len )
  		len = option_len;
  	memcpy ( data, option->data, len );
  
  	return option_len;
  }
  
  /**
   * Recalculate length of DHCP options block
   *
   * @v options		Uninitialised DHCP option block
   *
   * The "used length" field will be updated based on scanning through
   * the block to find the end of the options.
   */
  void dhcpopt_update_used_len ( struct dhcp_options *options ) {
  	struct dhcp_option *option;
  	int offset = 0;
  	ssize_t remaining = options->alloc_len;
  	unsigned int option_len;
  
  	/* Find last non-pad option */
  	options->used_len = 0;
  	while ( remaining ) {
  		option = dhcp_option ( options, offset );
  		option_len = dhcp_option_len ( option );
  		remaining -= option_len;
  		if ( remaining < 0 )
  			break;
  		offset += option_len;
  		if ( option->tag != DHCP_PAD )
  			options->used_len = offset;
  	}
  }
  
  /**
   * Initialise prepopulated block of DHCP options
   *
   * @v options		Uninitialised DHCP option block
   * @v data		Memory for DHCP option data
   * @v alloc_len		Length of memory for DHCP option data
   * @v realloc		DHCP option block reallocator
   *
   * The memory content must already be filled with valid DHCP options.
   * A zeroed block counts as a block of valid DHCP options.
   */
  void dhcpopt_init ( struct dhcp_options *options, void *data, size_t alloc_len,
  		    int ( * realloc ) ( struct dhcp_options *options,
  					size_t len ) ) {
  
  	/* Fill in fields */
  	options->data = data;
  	options->alloc_len = alloc_len;
  	options->realloc = realloc;
  
  	/* Update length */
  	dhcpopt_update_used_len ( options );
  
  	DBGC ( options, "DHCPOPT %p created (data %p lengths %#zx,%#zx)\n",
  	       options, options->data, options->used_len, options->alloc_len );
  }
  