[slam] Add Scalable Local Area Multicast (SLAM) protocol support

Tested against the mini-slamd server located in contrib/mini-slamd
with a single client, on a lossy network.

1 files changed, 749 insertions, 0 deletions

diff --git a/src/net/udp/slam.c b/src/net/udp/slam.c
new file mode 100644
index 00000000..67af8cba
--- /dev/null
+++ b/src/net/udp/slam.c
@@ -0,0 +1,749 @@
+/*
+ * 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+#include <errno.h>
+#include <assert.h>
+#include <byteswap.h>
+#include <gpxe/features.h>
+#include <gpxe/iobuf.h>
+#include <gpxe/bitmap.h>
+#include <gpxe/xfer.h>
+#include <gpxe/open.h>
+#include <gpxe/uri.h>
+#include <gpxe/tcpip.h>
+#include <gpxe/retry.h>
+
+/** @file
+ *
+ * Scalable Local Area Multicast protocol
+ *
+ * The SLAM protocol is supported only by Etherboot; it was designed
+ * and implemented by Eric Biederman.  A server implementation is
+ * available in contrib/mini-slamd.  There does not appear to be any
+ * documentation beyond a few sparse comments in Etherboot's
+ * proto_slam.c.
+ *
+ * SLAM packets use three types of data field:
+ *
+ *  Nul : A single NUL (0) byte, used as a list terminator
+ *
+ *  Raw : A block of raw data
+ *
+ *  Int : A variable-length integer, in big-endian order.  The length
+ *        of the integer is encoded in the most significant three bits.
+ *
+ * Packets received by the client have the following layout:
+ *
+ *  Int : Transaction identifier.  This is an opaque value.
+ *
+ *  Int : Total number of bytes in the transfer.
+ *
+ *  Int : Block size, in bytes.
+ *
+ *  Int : Packet sequence number within the transfer (if this packet
+ *        contains data).
+ *
+ *  Raw : Packet data (if this packet contains data).
+ *
+ * Packets transmitted by the client consist of a run-length-encoded
+ * representation of the received-blocks bitmap, looking something
+ * like:
+ *
+ *  Int : Number of consecutive successfully-received packets
+ *  Int : Number of consecutive missing packets
+ *  Int : Number of consecutive successfully-received packets
+ *  Int : Number of consecutive missing packets
+ *  ....
+ *  Nul
+ *
+ */
+
+FEATURE ( FEATURE_PROTOCOL, "SLAM", DHCP_EB_FEATURE_SLAM, 1 );
+
+/** Default SLAM server port */
+#define SLAM_DEFAULT_PORT 10000
+
+/** Default SLAM multicast IP address */
+#define SLAM_DEFAULT_MULTICAST_IP \
+	( ( 239 << 24 ) | ( 255 << 16 ) | ( 1 << 8 ) | ( 1 << 0 ) )
+
+/** Default SLAM multicast port */
+#define SLAM_DEFAULT_MULTICAST_PORT 10000
+
+/** Maximum SLAM header length */
+#define SLAM_MAX_HEADER_LEN ( 8 /* transaction id */ + 8 /* total_bytes */ + \
+			      8 /* block_size */ )
+
+/** A SLAM request */
+struct slam_request {
+	/** Reference counter */
+	struct refcnt refcnt;
+
+	/** Data transfer interface */
+	struct xfer_interface xfer;
+	/** Unicast socket */
+	struct xfer_interface socket;
+	/** Multicast socket */
+	struct xfer_interface mc_socket;
+
+	/** NACK timer */
+	struct retry_timer timer;
+
+	/** Cached header */
+	uint8_t header[SLAM_MAX_HEADER_LEN];
+	/** Size of cached header */
+	size_t header_len;
+	/** Total number of bytes in transfer */
+	unsigned long total_bytes;
+	/** Transfer block size */
+	unsigned long block_size;
+	/** Number of blocks in transfer */
+	unsigned long num_blocks;
+	/** Block bitmap */
+	struct bitmap bitmap;
+	/** NACK sent flag */
+	int nack_sent;
+};
+
+/**
+ * Free a SLAM request
+ *
+ * @v refcnt		Reference counter
+ */
+static void slam_free ( struct refcnt *refcnt ) {
+	struct slam_request *slam =
+		container_of ( refcnt, struct slam_request, refcnt );
+
+	bitmap_free ( &slam->bitmap );
+	free ( slam );
+}
+
+/**
+ * Mark SLAM request as complete
+ *
+ * @v slam		SLAM request
+ * @v rc		Return status code
+ */
+static void slam_finished ( struct slam_request *slam, int rc ) {
+	static const uint8_t slam_disconnect[] = { 0 };
+
+	DBGC ( slam, "SLAM %p finished with status code %d (%s)\n",
+	       slam, rc, strerror ( rc ) );
+
+	/* Send a disconnect message if we ever sent anything to the
+	 * server.
+	 */
+	if ( slam->nack_sent ) {
+		xfer_deliver_raw ( &slam->socket, slam_disconnect,
+				   sizeof ( slam_disconnect ) );
+	}
+
+	/* Stop the retry timer */
+	stop_timer ( &slam->timer );
+
+	/* Close all data transfer interfaces */
+	xfer_nullify ( &slam->socket );
+	xfer_close ( &slam->socket, rc );
+	xfer_nullify ( &slam->mc_socket );
+	xfer_close ( &slam->mc_socket, rc );
+	xfer_nullify ( &slam->xfer );
+	xfer_close ( &slam->xfer, rc );
+}
+
+/****************************************************************************
+ *
+ * TX datapath
+ *
+ */
+
+/**
+ * Add a variable-length value to a SLAM packet
+ *
+ * @v slam		SLAM request
+ * @v iobuf		I/O buffer
+ * @v value		Value to add
+ * @ret rc		Return status code
+ *
+ * Adds a variable-length value to the end of an I/O buffer.  Will
+ * refuse to use the last byte of the I/O buffer; this is to allow
+ * space for the terminating NUL.
+ */
+static int slam_put_value ( struct slam_request *slam,
+			    struct io_buffer *iobuf, unsigned long value ) {
+	uint8_t *data;
+	size_t len;
+	unsigned int i;
+
+	/* Calculate variable length required to store value.  Always
+	 * leave at least one byte in the I/O buffer.
+	 */
+	len = ( ( flsl ( value ) + 10 ) / 8 );
+	if ( len >= iob_tailroom ( iobuf ) ) {
+		DBGC ( slam, "SLAM %p cannot add %d-byte value\n",
+		       slam, len );
+		return -ENOBUFS;
+	}
+	/* There is no valid way within the protocol that we can end
+	 * up trying to push a full-sized long (i.e. without space for
+	 * the length encoding).
+	 */
+	assert ( len <= sizeof ( value ) );
+
+	/* Add value */
+	data = iob_put ( iobuf, len );
+	for ( i = len ; i-- ; ) {
+		data[i] = value;
+		value >>= 8;
+	}
+	*data |= ( len << 5 );
+	assert ( value == 0 );
+
+	return 0;
+}
+
+/**
+ * Send SLAM NACK packet
+ *
+ * @v slam		SLAM request
+ * @ret rc		Return status code
+ */
+static int slam_tx_nack ( struct slam_request *slam ) {
+	struct io_buffer *iobuf;
+	unsigned int block;
+	unsigned int block_count;
+	int block_present;
+	int last_block_present;
+	uint8_t *nul;
+
+	DBGC ( slam, "SLAM %p transmitting NACK\n", slam );
+
+	/* Mark NACK as sent, so that we know we have to disconnect later */
+	slam->nack_sent = 1;
+
+	/* Use the current block size as a good estimate of how much
+	 * data we can fit in a packet.  If we overrun, it seems to be
+	 * acceptable to drop information anyway.
+	 */
+	iobuf = xfer_alloc_iob ( &slam->socket,	slam->block_size );
+	if ( ! iobuf ) {
+		DBGC ( slam, "SLAM %p could not allocate I/O buffer\n",
+		       slam );
+		return -ENOMEM;
+	}
+
+	/* Walk bitmap to construct list */
+	block_count = 0;
+	last_block_present = ( ! 0 );
+	for ( block = 0 ; block < slam->num_blocks ; block++ ) {
+		block_present = ( !! bitmap_test ( &slam->bitmap, block ) );
+		if ( block_present != last_block_present ) {
+			slam_put_value ( slam, iobuf, block_count );
+			block_count = 0;
+			last_block_present = block_present;
+		}
+		block_count++;
+	}
+	slam_put_value ( slam, iobuf, block_count );
+
+	/* Add NUL terminator */
+	nul = iob_put ( iobuf, 1 );
+	*nul = 0;
+
+	/* Transmit packet */
+	return xfer_deliver_iob ( &slam->socket, iobuf );
+}
+
+/**
+ * Handle SLAM retransmission timer expiry
+ *
+ * @v timer		Retry timer
+ * @v fail		Failure indicator
+ */
+static void slam_timer_expired ( struct retry_timer *timer, int fail ) {
+	struct slam_request *slam =
+		container_of ( timer, struct slam_request, timer );
+
+	if ( fail ) {
+		slam_finished ( slam, -ETIMEDOUT );
+	} else {
+		start_timer ( timer );
+		slam_tx_nack ( slam );
+	}
+}
+
+/****************************************************************************
+ *
+ * RX datapath
+ *
+ */
+
+/**
+ * Read and strip a variable-length value from a SLAM packet
+ *
+ * @v slam		SLAM request
+ * @v iobuf		I/O buffer
+ * @v value		Value to fill in, or NULL to ignore value
+ * @ret rc		Return status code
+ *
+ * Reads a variable-length value from the start of the I/O buffer.  
+ */
+static int slam_pull_value ( struct slam_request *slam,
+			     struct io_buffer *iobuf,
+			     unsigned long *value ) {
+	uint8_t *data;
+	size_t len;
+
+	/* Sanity check */
+	if ( iob_len ( iobuf ) == 0 ) {
+		DBGC ( slam, "SLAM %p empty value\n", slam );
+		return -EINVAL;
+	}
+
+	/* Read and verify length of value */
+	data = iobuf->data;
+	len = ( *data >> 5 );
+	if ( ( len == 0 ) ||
+	     ( value && ( len > sizeof ( *value ) ) ) ) {
+		DBGC ( slam, "SLAM %p invalid value length %d bytes\n",
+		       slam, len );
+		return -EINVAL;
+	}
+	if ( len > iob_len ( iobuf ) ) {
+		DBGC ( slam, "SLAM %p value extends beyond I/O buffer\n",
+		       slam );
+		return -EINVAL;
+	}
+
+	/* Read value */
+	iob_pull ( iobuf, len );
+	*value = ( *data & 0x1f );
+	while ( --len ) {
+		*value <<= 8;
+		*value |= *(++data);
+	}
+
+	return 0;
+}
+
+/**
+ * Read and strip SLAM header
+ *
+ * @v slam		SLAM request
+ * @v iobuf		I/O buffer
+ * @ret rc		Return status code
+ */
+static int slam_pull_header ( struct slam_request *slam,
+			      struct io_buffer *iobuf ) {
+	void *header = iobuf->data;
+	int rc;
+
+	/* If header matches cached header, just pull it and return */
+	if ( ( slam->header_len <= iob_len ( iobuf ) ) &&
+	     ( memcmp ( slam->header, iobuf->data, slam->header_len ) == 0 )){
+		iob_pull ( iobuf, slam->header_len );
+		return 0;
+	}
+
+	DBGC ( slam, "SLAM %p detected changed header; resetting\n", slam );
+
+	/* Read and strip transaction ID, total number of bytes, and
+	 * block size.
+	 */
+	if ( ( rc = slam_pull_value ( slam, iobuf, NULL ) ) != 0 )
+		return rc;
+	if ( ( rc = slam_pull_value ( slam, iobuf,
+				      &slam->total_bytes ) ) != 0 )
+		return rc;
+	if ( ( rc = slam_pull_value ( slam, iobuf,
+				      &slam->block_size ) ) != 0 )
+		return rc;
+
+	/* Update the cached header */
+	slam->header_len = ( iobuf->data - header );
+	assert ( slam->header_len <= sizeof ( slam->header ) );
+	memcpy ( slam->header, header, slam->header_len );
+
+	/* Calculate number of blocks */
+	slam->num_blocks = ( ( slam->total_bytes + slam->block_size - 1 ) /
+			     slam->block_size );
+
+	DBGC ( slam, "SLAM %p has total bytes %ld, block size %ld, num "
+	       "blocks %ld\n", slam, slam->total_bytes, slam->block_size,
+	       slam->num_blocks );
+
+	/* Discard and reset the bitmap */
+	bitmap_free ( &slam->bitmap );
+	memset ( &slam->bitmap, 0, sizeof ( slam->bitmap ) );
+
+	/* Allocate a new bitmap */
+	if ( ( rc = bitmap_resize ( &slam->bitmap,
+				    slam->num_blocks ) ) != 0 ) {
+		/* Failure to allocate a bitmap is fatal */
+		DBGC ( slam, "SLAM %p could not allocate bitmap for %ld "
+		       "blocks: %s\n", slam, slam->num_blocks,
+		       strerror ( rc ) );
+		slam_finished ( slam, rc );
+		return rc;
+	}
+
+	/* Notify recipient of file size */
+	xfer_seek ( &slam->xfer, slam->total_bytes, SEEK_SET );
+
+	return 0;
+}
+
+/**
+ * Receive SLAM data packet
+ *
+ * @v mc_socket		SLAM multicast socket
+ * @v iobuf		I/O buffer
+ * @ret rc		Return status code
+ */
+static int slam_mc_socket_deliver ( struct xfer_interface *mc_socket,
+				    struct io_buffer *iobuf,
+				    struct xfer_metadata *rx_meta __unused ) {
+	struct slam_request *slam =
+		container_of ( mc_socket, struct slam_request, mc_socket );
+	struct xfer_metadata meta;
+	unsigned long packet;
+	size_t len;
+	int rc;
+
+	/* Hit the timer */
+	stop_timer ( &slam->timer );
+	start_timer ( &slam->timer );
+
+	/* Read and strip packet header */
+	if ( ( rc = slam_pull_header ( slam, iobuf ) ) != 0 )
+		goto err_discard;
+
+	/* Read and strip packet number */
+	if ( ( rc = slam_pull_value ( slam, iobuf, &packet ) ) != 0 )
+		goto err_discard;
+
+	/* Sanity check packet number */
+	if ( packet >= slam->num_blocks ) {
+		DBGC ( slam, "SLAM %p received out-of-range packet %ld "
+		       "(num_blocks=%ld)\n", slam, packet, slam->num_blocks );
+		rc = -EINVAL;
+		goto err_discard;
+	}
+
+	/* Sanity check length */
+	len = iob_len ( iobuf );
+	if ( len > slam->block_size ) {
+		DBGC ( slam, "SLAM %p received oversize packet of %zd bytes "
+		       "(block_size=%ld)\n", slam, len, slam->block_size );
+		rc = -EINVAL;
+		goto err_discard;
+	}
+	if ( ( packet != ( slam->num_blocks - 1 ) ) &&
+	     ( len < slam->block_size ) ) {
+		DBGC ( slam, "SLAM %p received short packet of %zd bytes "
+		       "(block_size=%ld)\n", slam, len, slam->block_size );
+		rc = -EINVAL;
+		goto err_discard;
+	}
+
+	/* If we have already seen this packet, discard it */
+	if ( bitmap_test ( &slam->bitmap, packet ) ) {
+		goto discard;
+	}
+
+	/* Pass to recipient */
+	memset ( &meta, 0, sizeof ( meta ) );
+	meta.whence = SEEK_SET;
+	meta.offset = ( packet * slam->block_size );
+	if ( ( rc = xfer_deliver_iob_meta ( &slam->xfer, iobuf,
+					    &meta ) ) != 0 )
+		goto err;
+
+	/* Mark block as received */
+	bitmap_set ( &slam->bitmap, packet );
+
+	/* If we have received all blocks, terminate */
+	if ( bitmap_full ( &slam->bitmap ) )
+		slam_finished ( slam, 0 );
+
+	return 0;
+
+ err_discard:
+ discard:
+	free_iob ( iobuf );
+ err:
+	return rc;
+}
+
+/**
+ * Receive SLAM non-data packet
+ *
+ * @v socket		SLAM unicast socket
+ * @v iobuf		I/O buffer
+ * @ret rc		Return status code
+ */
+static int slam_socket_deliver ( struct xfer_interface *socket,
+				 struct io_buffer *iobuf,
+				 struct xfer_metadata *rx_meta __unused ) {
+	struct slam_request *slam =
+		container_of ( socket, struct slam_request, socket );
+	int rc;
+
+	/* Hit the timer */
+	stop_timer ( &slam->timer );
+	start_timer ( &slam->timer );
+
+	/* Read and strip packet header */
+	if ( ( rc = slam_pull_header ( slam, iobuf ) ) != 0 )
+		goto discard;
+
+	/* Sanity check */
+	if ( iob_len ( iobuf ) != 0 ) {
+		DBGC ( slam, "SLAM %p received trailing garbage:\n", slam );
+		DBGC_HD ( slam, iobuf->data, iob_len ( iobuf ) );
+		rc = -EINVAL;
+		goto discard;
+	}
+
+	/* Discard packet */
+	free_iob ( iobuf );
+
+	/* Send NACK in reply */
+	slam_tx_nack ( slam );
+
+	return 0;
+
+ discard:
+	free_iob ( iobuf );
+	return rc;
+
+}
+
+/**
+ * Close SLAM unicast socket
+ *
+ * @v socket		SLAM unicast socket
+ * @v rc		Reason for close
+ */
+static void slam_socket_close ( struct xfer_interface *socket, int rc ) {
+	struct slam_request *slam =
+		container_of ( socket, struct slam_request, socket );
+
+	DBGC ( slam, "SLAM %p unicast socket closed: %s\n",
+	       slam, strerror ( rc ) );
+
+	slam_finished ( slam, rc );
+}
+
+/** SLAM unicast socket data transfer operations */
+static struct xfer_interface_operations slam_socket_operations = {
+	.close		= slam_socket_close,
+	.vredirect	= xfer_vopen,
+	.window		= unlimited_xfer_window,
+	.alloc_iob	= default_xfer_alloc_iob,
+	.deliver_iob	= slam_socket_deliver,
+	.deliver_raw	= xfer_deliver_as_iob,
+};
+
+/**
+ * Close SLAM multicast socket
+ *
+ * @v mc_socket		SLAM multicast socket
+ * @v rc		Reason for close
+ */
+static void slam_mc_socket_close ( struct xfer_interface *mc_socket, int rc ){
+	struct slam_request *slam =
+		container_of ( mc_socket, struct slam_request, mc_socket );
+
+	DBGC ( slam, "SLAM %p multicast socket closed: %s\n",
+	       slam, strerror ( rc ) );
+
+	slam_finished ( slam, rc );
+}
+
+/** SLAM multicast socket data transfer operations */
+static struct xfer_interface_operations slam_mc_socket_operations = {
+	.close		= slam_mc_socket_close,
+	.vredirect	= xfer_vopen,
+	.window		= unlimited_xfer_window,
+	.alloc_iob	= default_xfer_alloc_iob,
+	.deliver_iob	= slam_mc_socket_deliver,
+	.deliver_raw	= xfer_deliver_as_iob,
+};
+
+/****************************************************************************
+ *
+ * Data transfer interface
+ *
+ */
+
+/**
+ * Close SLAM data transfer interface
+ *
+ * @v xfer		SLAM data transfer interface
+ * @v rc		Reason for close
+ */
+static void slam_xfer_close ( struct xfer_interface *xfer, int rc ) {
+	struct slam_request *slam =
+		container_of ( xfer, struct slam_request, xfer );
+
+	DBGC ( slam, "SLAM %p data transfer interface closed: %s\n",
+	       slam, strerror ( rc ) );
+
+	slam_finished ( slam, rc );
+}
+
+/** SLAM data transfer operations */
+static struct xfer_interface_operations slam_xfer_operations = {
+	.close		= slam_xfer_close,
+	.vredirect	= ignore_xfer_vredirect,
+	.window		= unlimited_xfer_window,
+	.alloc_iob	= default_xfer_alloc_iob,
+	.deliver_iob	= xfer_deliver_as_raw,
+	.deliver_raw	= ignore_xfer_deliver_raw,
+};
+
+/**
+ * Parse SLAM URI multicast address
+ *
+ * @v slam		SLAM request
+ * @v path		Path portion of x-slam:// URI
+ * @v address		Socket address to fill in
+ * @ret rc		Return status code
+ */
+static int slam_parse_multicast_address ( struct slam_request *slam,
+					  const char *path,
+					  struct sockaddr_in *address ) {
+	char path_dup[ strlen ( path ) + 1 ];
+	char *sep;
+
+	/* Create temporary copy of path */
+	memcpy ( path_dup, path, sizeof ( path_dup ) );
+
+	/* Parse port, if present */
+	sep = strchr ( path_dup, ':' );
+	if ( sep ) {
+		*(sep++) = '\0';
+		address->sin_port = htons ( strtoul ( sep, &sep, 0 ) );
+		if ( *sep != '\0' ) {
+			DBGC ( slam, "SLAM %p invalid multicast port\n",
+			       slam );
+			return -EINVAL;
+		}
+	}
+
+	/* Parse address */
+	if ( inet_aton ( path_dup, &address->sin_addr ) == 0 ) {
+		DBGC ( slam, "SLAM %p invalid multicast address\n", slam );
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * Initiate a SLAM request
+ *
+ * @v xfer		Data transfer interface
+ * @v uri		Uniform Resource Identifier
+ * @ret rc		Return status code
+ */
+static int slam_open ( struct xfer_interface *xfer, struct uri *uri ) {
+	static const struct sockaddr_in default_multicast = {
+		.sin_family = AF_INET,
+		.sin_port = htons ( SLAM_DEFAULT_MULTICAST_PORT ),
+		.sin_addr = { htonl ( SLAM_DEFAULT_MULTICAST_IP ) },
+	};
+	struct slam_request *slam;
+	struct sockaddr_tcpip server;
+	struct sockaddr_in multicast;
+	int rc;
+
+	/* Sanity checks */
+	if ( ! uri->host )
+		return -EINVAL;
+
+	/* Allocate and populate structure */
+	slam = zalloc ( sizeof ( *slam ) );
+	if ( ! slam )
+		return -ENOMEM;
+	slam->refcnt.free = slam_free;
+	xfer_init ( &slam->xfer, &slam_xfer_operations, &slam->refcnt );
+	xfer_init ( &slam->socket, &slam_socket_operations, &slam->refcnt );
+	xfer_init ( &slam->mc_socket, &slam_mc_socket_operations,
+		    &slam->refcnt );
+	slam->timer.expired = slam_timer_expired;
+	/* Fake an invalid cached header of { 0x00, ... } */
+	slam->header_len = 1;
+	/* Fake parameters for initial NACK */
+	slam->block_size = 512;
+	slam->num_blocks = 1;
+	if ( ( rc = bitmap_resize ( &slam->bitmap, 1 ) ) != 0 ) {
+		DBGC ( slam, "SLAM %p could not allocate initial bitmap: "
+		       "%s\n", slam, strerror ( rc ) );
+		goto err;
+	}
+
+	/* Open unicast socket */
+	memset ( &server, 0, sizeof ( server ) );
+	server.st_port = htons ( uri_port ( uri, SLAM_DEFAULT_PORT ) );
+	if ( ( rc = xfer_open_named_socket ( &slam->socket, SOCK_DGRAM,
+					     ( struct sockaddr * ) &server,
+					     uri->host, NULL ) ) != 0 ) {
+		DBGC ( slam, "SLAM %p could not open unicast socket: %s\n",
+		       slam, strerror ( rc ) );
+		goto err;
+	}
+
+	/* Open multicast socket */
+	memcpy ( &multicast, &default_multicast, sizeof ( multicast ) );
+	if ( uri->path && 
+	     ( ( rc = slam_parse_multicast_address ( slam, uri->path,
+						     &multicast ) ) != 0 ) ) {
+		goto err;
+	}
+	if ( ( rc = xfer_open_socket ( &slam->mc_socket, SOCK_DGRAM,
+				 ( struct sockaddr * ) &multicast,
+				 ( struct sockaddr * ) &multicast ) ) != 0 ) {
+		DBGC ( slam, "SLAM %p could not open multicast socket: %s\n",
+		       slam, strerror ( rc ) );
+		goto err;
+	}
+
+	/* Start retry timer */
+	start_timer ( &slam->timer );
+
+	/* Attach to parent interface, mortalise self, and return */
+	xfer_plug_plug ( &slam->xfer, xfer );
+	ref_put ( &slam->refcnt );
+	return 0;
+
+ err:
+	slam_finished ( slam, rc );
+	ref_put ( &slam->refcnt );
+	return rc;
+}
+
+/** SLAM URI opener */
+struct uri_opener slam_uri_opener __uri_opener = {
+	.scheme	= "x-slam",
+	.open	= slam_open,
+};