[dhcp] Allow use of custom reallocation functions for DHCP option blocks

Allow functions other than realloc() to be used to reallocate DHCP
option block data, and specify the reallocation function at the time
of calling dhcpopt_init().

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/nvo.c

@@ -133,7 +133,8 @@ static void nvo_init_dhcpopts ( struct nvo_block *nvo ) {
 		memset ( nvo->data, 0, nvo->total_len );
 	}
 
-	dhcpopt_init ( &nvo->dhcpopts, options_data, options_len );
+	dhcpopt_init ( &nvo->dhcpopts, options_data, options_len,
+		       dhcpopt_no_realloc );
 }
 
 /**

src/include/ipxe/dhcpopts.h

@@ -19,16 +19,23 @@ struct dhcp_options {
 	size_t used_len;
 	/** Option block allocated length */
 	size_t alloc_len;
+	/** Reallocate option block raw data
+	 *
+	 * @v options		DHCP option block
+	 * @v len		New length
+	 * @ret rc		Return status code
+	 */
+	int ( * realloc ) ( struct dhcp_options *options, size_t len );
 };
 
 extern int dhcpopt_store ( struct dhcp_options *options, unsigned int tag,
 			   const void *data, size_t len );
-extern int dhcpopt_extensible_store ( struct dhcp_options *options,
-				      unsigned int tag,
-				      const void *data, size_t len );
 extern int dhcpopt_fetch ( struct dhcp_options *options, unsigned int tag,
 			   void *data, size_t len );
 extern void dhcpopt_init ( struct dhcp_options *options,
-			   void *data, size_t alloc_len );
+			   void *data, size_t alloc_len,
+			   int ( * realloc ) ( struct dhcp_options *options,
+					       size_t len ) );
+extern int dhcpopt_no_realloc ( struct dhcp_options *options, size_t len );
 
 #endif /* _IPXE_DHCPOPTS_H */

src/net/dhcpopts.c

@@ -169,6 +169,17 @@ static int find_dhcp_option_with_encap ( struct dhcp_options *options,
 	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
  *
@@ -177,46 +188,44 @@ static int find_dhcp_option_with_encap ( struct dhcp_options *options,
  * @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)
- * @v can_realloc	Can reallocate options data if necessary
  * @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,
-				int can_realloc ) {
+				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 new_options_len;
+	size_t old_alloc_len;
+	size_t new_used_len;
 	size_t new_encapsulator_len;
-	void *new_data;
 	void *source;
 	void *dest;
 	void *end;
+	int rc;
 
-	/* Check for sufficient space, and update length fields */
+	/* Check for sufficient space */
 	if ( new_len > DHCP_MAX_LEN ) {
 		DBGC ( options, "DHCPOPT %p overlength option\n", options );
 		return -ENOSPC;
 	}
-	new_options_len = ( options->used_len + delta );
-	if ( new_options_len > options->alloc_len ) {
-		/* Reallocate options block if allowed to do so. */
-		if ( can_realloc ) {
-			new_data = realloc ( options->data, new_options_len );
-			if ( ! new_data ) {
-				DBGC ( options, "DHCPOPT %p could not "
-				       "reallocate to %zd bytes\n", options,
-				       new_options_len );
-				return -ENOMEM;
-			}
-			options->data = new_data;
-			options->alloc_len = new_options_len;
-		} else {
-			DBGC ( options, "DHCPOPT %p out of space\n", options );
-			return -ENOMEM;
+	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 );
@@ -227,7 +236,9 @@ static int resize_dhcp_option ( struct dhcp_options *options,
 		}
 		encapsulator->len = new_encapsulator_len;
 	}
-	options->used_len = new_options_len;
+
+	/* Update used length */
+	options->used_len = new_used_len;
 
 	/* Move remainder of option data */
 	option = dhcp_option ( options, offset );
@@ -236,6 +247,15 @@ static int resize_dhcp_option ( struct dhcp_options *options,
 	end = ( options->data + options->alloc_len );
 	memmove ( dest, source, ( end - dest ) );
 
+	/* 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;
 }
 
@@ -246,7 +266,6 @@ static int resize_dhcp_option ( struct dhcp_options *options,
  * @v tag		DHCP option tag
  * @v data		New value for DHCP option
  * @v len		Length of value, in bytes
- * @v can_realloc	Can reallocate options data if necessary
  * @ret offset		Offset of DHCP option, or negative error
  *
  * Sets the value of a DHCP option within the options block.  The
@@ -258,9 +277,8 @@ static int resize_dhcp_option ( struct dhcp_options *options,
  * be left with its original value.
  */
 static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
-			     const void *data, size_t len,
-			     int can_realloc ) {
-	static const uint8_t empty_encapsulator[] = { DHCP_END };
+			     const void *data, size_t len ) {
+	static const uint8_t empty_encap[] = { DHCP_END };
 	int offset;
 	int encap_offset = -1;
 	int creation_offset;
@@ -291,10 +309,12 @@ static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
 
 	/* Ensure that encapsulator exists, if required */
 	if ( encap_tag ) {
-		if ( encap_offset < 0 )
-			encap_offset = set_dhcp_option ( options, encap_tag,
-							 empty_encapsulator, 1,
-							 can_realloc );
+		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 );
@@ -306,8 +326,7 @@ static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
 
 	/* Resize option to fit new data */
 	if ( ( rc = resize_dhcp_option ( options, offset, encap_offset,
-					 old_len, new_len,
-					 can_realloc ) ) != 0 )
+					 old_len, new_len ) ) != 0 )
 		return rc;
 
 	/* Copy new data into option, if applicable */
@@ -322,7 +341,7 @@ static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
 	if ( encap_offset >= 0 ) {
 		option = dhcp_option ( options, encap_offset );
 		if ( option->len <= 1 )
-			set_dhcp_option ( options, encap_tag, NULL, 0, 0 );
+			set_dhcp_option ( options, encap_tag, NULL, 0 );
 	}
 
 	return offset;
@@ -341,26 +360,7 @@ 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, 0 );
-	if ( offset < 0 )
-		return offset;
-	return 0;
-}
-
-/**
- * Store value of DHCP option setting, extending options block if necessary
- *
- * @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_extensible_store ( struct dhcp_options *options, unsigned int tag,
-			       const void *data, size_t len ) {
-	int offset;
-
-	offset = set_dhcp_option ( options, tag, data, len, 1 );
+	offset = set_dhcp_option ( options, tag, data, len );
 	if ( offset < 0 )
 		return offset;
 	return 0;
@@ -428,16 +428,19 @@ static void dhcpopt_update_used_len ( struct dhcp_options *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 ) {
+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 );

src/net/dhcppkt.c

@@ -267,7 +267,8 @@ void dhcppkt_init ( struct dhcp_packet *dhcppkt, struct dhcphdr *data,
 	ref_init ( &dhcppkt->refcnt, NULL );
 	dhcppkt->dhcphdr = data;
 	dhcpopt_init ( &dhcppkt->options, &dhcppkt->dhcphdr->options,
-		       ( len - offsetof ( struct dhcphdr, options ) ) );
+		       ( len - offsetof ( struct dhcphdr, options ) ),
+		       dhcpopt_no_realloc );
 	settings_init ( &dhcppkt->settings,
 			&dhcppkt_settings_operations, &dhcppkt->refcnt, 0 );
 }