fragment.c

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/*
 * 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.
 *
 * 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 <string.h>
#include <ipxe/retry.h>
#include <ipxe/timer.h>
#include <ipxe/ipstat.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 );
        fragment->fragments->stats->reasm_fails++;
        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;

        /* Update statistics */
        fragments->stats->reasm_reqds++;

        /* 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 );
                fragment->fragments = fragments;
                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 );
                        fragments->stats->reasm_oks++;
                        return iobuf;
                }
        }

        /* (Re)start fragment reassembly timer */
        start_timer_fixed ( &fragment->timer, FRAGMENT_TIMEOUT );

        return NULL;

 drop:
        fragments->stats->reasm_fails++;
        free_iob ( iobuf );
        return NULL;
}