[ipv4] Generalise fragment reassembly mechanism

Generalise the concept of fragment reassembly to allow for code
sharing between IPv4 and IPv6 protocols.

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

src/net/fragment.c

@@ -0,0 +1,172 @@
+/*
+ * Copyright (C) 2013 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.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ipxe/retry.h>
+#include <ipxe/timer.h>
+#include <ipxe/fragment.h>
+
+/** @file
+ *
+ * Fragment reassembly
+ *
+ */
+
+/**
+ * Expire fragment reassembly buffer
+ *
+ * @v timer		Retry timer
+ * @v fail		Failure indicator
+ */
+static void fragment_expired ( struct retry_timer *timer, int fail __unused ) {
+	struct fragment *fragment =
+		container_of ( timer, struct fragment, timer );
+
+	DBGC ( fragment, "FRAG %p expired\n", fragment );
+	free_iob ( fragment->iobuf );
+	list_del ( &fragment->list );
+	free ( fragment );
+}
+
+/**
+ * Find fragment reassembly buffer
+ *
+ * @v fragments		Fragment reassembler
+ * @v iobuf		I/O buffer
+ * @v hdrlen		Length of non-fragmentable potion of I/O buffer
+ * @ret fragment	Fragment reassembly buffer, or NULL if not found
+ */
+static struct fragment * fragment_find ( struct fragment_reassembler *fragments,
+					 struct io_buffer *iobuf,
+					 size_t hdrlen ) {
+	struct fragment *fragment;
+
+	list_for_each_entry ( fragment, &fragments->list, list ) {
+		if ( fragments->is_fragment ( fragment, iobuf, hdrlen ) )
+			return fragment;
+	}
+	return NULL;
+}
+
+/**
+ * Reassemble packet
+ *
+ * @v fragments		Fragment reassembler
+ * @v iobuf		I/O buffer
+ * @v hdrlen		Length of non-fragmentable potion of I/O buffer
+ * @ret iobuf		Reassembled packet, or NULL
+ *
+ * This function takes ownership of the I/O buffer.  Note that the
+ * length of the non-fragmentable portion may be modified.
+ */
+struct io_buffer * fragment_reassemble ( struct fragment_reassembler *fragments,
+					 struct io_buffer *iobuf,
+					 size_t *hdrlen ) {
+	struct fragment *fragment;
+	struct io_buffer *new_iobuf;
+	size_t new_len;
+	size_t offset;
+	size_t expected_offset;
+	int more_frags;
+
+	/* Find matching fragment reassembly buffer, if any */
+	fragment = fragment_find ( fragments, iobuf, *hdrlen );
+
+	/* Drop out-of-order fragments */
+	offset = fragments->fragment_offset ( iobuf, *hdrlen );
+	expected_offset = ( fragment ? ( iob_len ( fragment->iobuf ) -
+					 fragment->hdrlen ) : 0 );
+	if ( offset != expected_offset ) {
+		DBGC ( fragment, "FRAG %p dropping out-of-sequence fragment "
+		       "[%zd,%zd), expected [%zd,...)\n", fragment, offset,
+		       ( offset + iob_len ( iobuf ) - *hdrlen ),
+		       expected_offset );
+		goto drop;
+	}
+
+	/* Create or extend fragment reassembly buffer as applicable */
+	if ( ! fragment ) {
+
+		/* Create new fragment reassembly buffer */
+		fragment = zalloc ( sizeof ( *fragment ) );
+		if ( ! fragment )
+			goto drop;
+		list_add ( &fragment->list, &fragments->list );
+		fragment->iobuf = iobuf;
+		fragment->hdrlen = *hdrlen;
+		timer_init ( &fragment->timer, fragment_expired, NULL );
+		DBGC ( fragment, "FRAG %p [0,%zd)\n", fragment,
+		       ( iob_len ( iobuf ) - *hdrlen ) );
+
+	} else {
+
+		/* Check if this is the final fragment */
+		more_frags = fragments->more_fragments ( iobuf, *hdrlen );
+		DBGC ( fragment, "FRAG %p [%zd,%zd)%s\n", fragment,
+		       offset, ( offset + iob_len ( iobuf ) - *hdrlen ),
+		       ( more_frags ? "" : " complete" ) );
+
+		/* Extend fragment reassembly buffer.  Preserve I/O
+		 * buffer headroom to allow for code which modifies
+		 * and resends the buffer (e.g. ICMP echo responses).
+		 */
+		iob_pull ( iobuf, *hdrlen );
+		new_len = ( iob_headroom ( fragment->iobuf ) +
+			    iob_len ( fragment->iobuf ) + iob_len ( iobuf ) );
+		new_iobuf = alloc_iob ( new_len );
+		if ( ! new_iobuf ) {
+			DBGC ( fragment, "FRAG %p could not extend reassembly "
+			       "buffer to %zd bytes\n", fragment, new_len );
+			goto drop;
+		}
+		iob_reserve ( new_iobuf, iob_headroom ( fragment->iobuf ) );
+		memcpy ( iob_put ( new_iobuf, iob_len ( fragment->iobuf ) ),
+			 fragment->iobuf->data, iob_len ( fragment->iobuf ) );
+		memcpy ( iob_put ( new_iobuf, iob_len ( iobuf ) ),
+			 iobuf->data, iob_len ( iobuf ) );
+		free_iob ( fragment->iobuf );
+		fragment->iobuf = new_iobuf;
+		free_iob ( iobuf );
+
+		/* Stop fragment reassembly timer */
+		stop_timer ( &fragment->timer );
+
+		/* If this is the final fragment, return it */
+		if ( ! more_frags ) {
+			iobuf = fragment->iobuf;
+			*hdrlen = fragment->hdrlen;
+			list_del ( &fragment->list );
+			free ( fragment );
+			return iobuf;
+		}
+	}
+
+	/* (Re)start fragment reassembly timer */
+	start_timer_fixed ( &fragment->timer, FRAGMENT_TIMEOUT );
+
+	return NULL;
+
+ drop:
+	free_iob ( iobuf );
+	return NULL;
+}