tcp_pcap.c

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/*-
 * Copyright (c) 2015
 *      Jonathan Looney. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD$
 */
 
#include <sys/queue.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/eventhandler.h>
#include <machine/atomic.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_pcap.h>
 
#define M_LEADINGSPACE_NOWRITE(m)                                       \
        ((m)->m_data - M_START(m))
 
int tcp_pcap_aggressive_free = 1;
static int tcp_pcap_clusters_referenced_cur = 0;
static int tcp_pcap_clusters_referenced_max = 0;
 
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_aggressive_free,
        CTLFLAG_RW, &tcp_pcap_aggressive_free, 0,
        "Free saved packets when the memory system comes under pressure");
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_clusters_referenced_cur,
        CTLFLAG_RD, &tcp_pcap_clusters_referenced_cur, 0,
        "Number of clusters currently referenced on TCP PCAP queues");
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_clusters_referenced_max,
        CTLFLAG_RW, &tcp_pcap_clusters_referenced_max, 0,
        "Maximum number of clusters allowed to be referenced on TCP PCAP "
        "queues");
 
static int tcp_pcap_alloc_reuse_ext = 0;
static int tcp_pcap_alloc_reuse_mbuf = 0;
static int tcp_pcap_alloc_new_mbuf = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_alloc_reuse_ext,
        CTLFLAG_RD, &tcp_pcap_alloc_reuse_ext, 0,
        "Number of mbufs with external storage reused for the TCP PCAP "
        "functionality");
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_alloc_reuse_mbuf,
        CTLFLAG_RD, &tcp_pcap_alloc_reuse_mbuf, 0,
        "Number of mbufs with internal storage reused for the TCP PCAP "
        "functionality");
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_alloc_new_mbuf,
        CTLFLAG_RD, &tcp_pcap_alloc_new_mbuf, 0,
        "Number of new mbufs allocated for the TCP PCAP functionality");
 
VNET_DEFINE(int, tcp_pcap_packets) = 0;
#define V_tcp_pcap_packets      VNET(tcp_pcap_packets)
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_pcap_packets,
        CTLFLAG_RW, &VNET_NAME(tcp_pcap_packets), 0,
        "Default number of packets saved per direction per TCPCB");
 
/* Initialize the values. */
static void
tcp_pcap_max_set(void)
{
 
        tcp_pcap_clusters_referenced_max = nmbclusters / 4;
}
 
void
tcp_pcap_init(void)
{
 
        tcp_pcap_max_set();
        EVENTHANDLER_REGISTER(nmbclusters_change, tcp_pcap_max_set,
                NULL, EVENTHANDLER_PRI_ANY);
}
 
/*
 * If we are below the maximum allowed cluster references,
 * increment the reference count and return TRUE. Otherwise,
 * leave the reference count alone and return FALSE.
 */
static __inline bool
tcp_pcap_take_cluster_reference(void)
{
        if (atomic_fetchadd_int(&tcp_pcap_clusters_referenced_cur, 1) >=
                tcp_pcap_clusters_referenced_max) {
                atomic_add_int(&tcp_pcap_clusters_referenced_cur, -1);
                return FALSE;
        }
        return TRUE;
}
 
/*
 * For all the external entries in m, apply the given adjustment.
 * This can be used to adjust the counter when an mbuf chain is
 * copied or freed.
 */
static __inline void
tcp_pcap_adj_cluster_reference(struct mbuf *m, int adj)
{
        while (m) {
                if (m->m_flags & M_EXT)
                        atomic_add_int(&tcp_pcap_clusters_referenced_cur, adj);
 
                m = m->m_next;
        }
}
 
/*
 * Free all mbufs in a chain, decrementing the reference count as
 * necessary.
 *
 * Functions in this file should use this instead of m_freem() when
 * they are freeing mbuf chains that may contain clusters that were
 * already included in tcp_pcap_clusters_referenced_cur.
 */
static void
tcp_pcap_m_freem(struct mbuf *mb)
{
        while (mb != NULL) {
                if (mb->m_flags & M_EXT)
                        atomic_subtract_int(&tcp_pcap_clusters_referenced_cur,
                            1);
                mb = m_free(mb);
        }
}
 
/*
 * Copy data from m to n, where n cannot fit all the data we might
 * want from m.
 *
 * Prioritize data like this:
 * 1. TCP header
 * 2. IP header
 * 3. Data
 */
static void
tcp_pcap_copy_bestfit(struct tcphdr *th, struct mbuf *m, struct mbuf *n)
{
        struct mbuf *m_cur = m;
        int bytes_to_copy=0, trailing_data, skip=0, tcp_off;
 
        /* Below, we assume these will be non-NULL. */
        KASSERT(th, ("%s: called with th == NULL", __func__));
        KASSERT(m, ("%s: called with m == NULL", __func__));
        KASSERT(n, ("%s: called with n == NULL", __func__));
 
        /* We assume this initialization occurred elsewhere. */
        KASSERT(n->m_len == 0, ("%s: called with n->m_len=%d (expected 0)",
                __func__, n->m_len));
        KASSERT(n->m_data == M_START(n),
                ("%s: called with n->m_data != M_START(n)", __func__));
 
        /*
         * Calculate the size of the TCP header. We use this often
         * enough that it is worth just calculating at the start.
         */
        tcp_off = th->th_off << 2;
 
        /* Trim off leading empty mbufs. */
        while (m && m->m_len == 0)
                m = m->m_next;
 
        if (m) {
                m_cur = m;
        }
        else {
                /*
                 * No data? Highly unusual. We would expect to at
                 * least see a TCP header in the mbuf.
                 * As we have a pointer to the TCP header, I guess
                 * we should just copy that. (???)
                 */
fallback:
                bytes_to_copy = tcp_off;
                if (bytes_to_copy > M_SIZE(n))
                        bytes_to_copy = M_SIZE(n);
                bcopy(th, n->m_data, bytes_to_copy);
                n->m_len = bytes_to_copy;
                return;
        }
 
        /*
         * Find TCP header. Record the total number of bytes up to,
         * and including, the TCP header.
         */
        while (m_cur) {
                if ((caddr_t) th >= (caddr_t) m_cur->m_data &&
                        (caddr_t) th < (caddr_t) (m_cur->m_data + m_cur->m_len))
                        break;
                bytes_to_copy += m_cur->m_len;
                m_cur = m_cur->m_next;
        }
        if (m_cur)
                bytes_to_copy += (caddr_t) th - (caddr_t) m_cur->m_data;
        else
                goto fallback;
        bytes_to_copy += tcp_off;
 
        /*
         * If we already want to copy more bytes than we can hold
         * in the destination mbuf, skip leading bytes and copy
         * what we can.
         *
         * Otherwise, consider trailing data.
         */
        if (bytes_to_copy > M_SIZE(n)) {
                skip  = bytes_to_copy - M_SIZE(n);
                bytes_to_copy = M_SIZE(n);
        }
        else {
                /*
                 * Determine how much trailing data is in the chain.
                 * We start with the length of this mbuf (the one
                 * containing th) and subtract the size of the TCP
                 * header (tcp_off) and the size of the data prior
                 * to th (th - m_cur->m_data).
                 *
                 * This *should not* be negative, as the TCP code
                 * should put the whole TCP header in a single
                 * mbuf. But, it isn't a problem if it is. We will
                 * simple work off our negative balance as we look
                 * at subsequent mbufs.
                 */
                trailing_data = m_cur->m_len - tcp_off;
                trailing_data -= (caddr_t) th - (caddr_t) m_cur->m_data;
                m_cur = m_cur->m_next;
                while (m_cur) {
                        trailing_data += m_cur->m_len;
                        m_cur = m_cur->m_next;
                }
                if ((bytes_to_copy + trailing_data) > M_SIZE(n))
                        bytes_to_copy = M_SIZE(n);
                else
                        bytes_to_copy += trailing_data;
        }
 
        m_copydata(m, skip, bytes_to_copy, n->m_data);
        n->m_len = bytes_to_copy;
}
 
void
tcp_pcap_add(struct tcphdr *th, struct mbuf *m, struct mbufq *queue)
{
        struct mbuf *n = NULL, *mhead;
 
        KASSERT(th, ("%s: called with th == NULL", __func__));
        KASSERT(m, ("%s: called with m == NULL", __func__));
        KASSERT(queue, ("%s: called with queue == NULL", __func__));
 
        /* We only care about data packets. */
        while (m && m->m_type != MT_DATA)
                m = m->m_next;
 
        /* We only need to do something if we still have an mbuf. */
        if (!m)
                return;
 
        /* If we are not saving mbufs, return now. */
        if (queue->mq_maxlen == 0)
                return;
 
        /*
         * Check to see if we will need to recycle mbufs.
         *
         * If we need to get rid of mbufs to stay below
         * our packet count, try to reuse the mbuf. Once
         * we already have a new mbuf (n), then we can
         * simply free subsequent mbufs.
         *
         * Note that most of the logic in here is to deal
         * with the reuse. If we are fine with constant
         * mbuf allocs/deallocs, we could ditch this logic.
         * But, it only seems to make sense to reuse
         * mbufs we already have.
         */
        while (mbufq_full(queue)) {
                mhead = mbufq_dequeue(queue);
 
                if (n) {
                        tcp_pcap_m_freem(mhead);
                }
                else {
                        /*
                         * If this held an external cluster, try to
                         * detach the cluster. But, if we held the
                         * last reference, go through the normal
                         * free-ing process.
                         */
                        if (mhead->m_flags & M_EXTPG) {
                                /* Don't mess around with these. */
                                tcp_pcap_m_freem(mhead);
                                continue;
                        } else if (mhead->m_flags & M_EXT) {
                                switch (mhead->m_ext.ext_type) {
                                case EXT_SFBUF:
                                        /* Don't mess around with these. */
                                        tcp_pcap_m_freem(mhead);
                                        continue;
                                default:
                                        if (atomic_fetchadd_int(
                                                mhead->m_ext.ext_cnt, -1) == 1)
                                        {
                                                /*
                                                 * We held the last reference
                                                 * on this cluster. Restore
                                                 * the reference count and put
                                                 * it back in the pool.
                                                 */
                                                *(mhead->m_ext.ext_cnt) = 1;
                                                tcp_pcap_m_freem(mhead);
                                                continue;
                                        }
                                        /*
                                         * We were able to cleanly free the
                                         * reference.
                                         */
                                        atomic_subtract_int(
                                            &tcp_pcap_clusters_referenced_cur,
                                            1);
                                        tcp_pcap_alloc_reuse_ext++;
                                        break;
                                }
                        } else {
                                tcp_pcap_alloc_reuse_mbuf++;
                        }
 
                        n = mhead;
                        tcp_pcap_m_freem(n->m_next);
                        m_init(n, M_NOWAIT, MT_DATA, 0);
                }
        }
 
        /* Check to see if we need to get a new mbuf. */
        if (!n) {
                if (!(n = m_get(M_NOWAIT, MT_DATA)))
                        return;
                tcp_pcap_alloc_new_mbuf++;
        }
 
        /*
         * What are we dealing with? If a cluster, attach it. Otherwise,
         * try to copy the data from the beginning of the mbuf to the
         * end of data. (There may be data between the start of the data
         * area and the current data pointer. We want to get this, because
         * it may contain header information that is useful.)
         * In cases where that isn't possible, settle for what we can
         * get.
         */
        if ((m->m_flags & (M_EXT|M_EXTPG)) &&
            tcp_pcap_take_cluster_reference()) {
                n->m_data = m->m_data;
                n->m_len = m->m_len;
                mb_dupcl(n, m);
        }
        else if (((m->m_data + m->m_len) - M_START(m)) <= M_SIZE(n)) {
                /*
                 * At this point, n is guaranteed to be a normal mbuf
                 * with no cluster and no packet header. Because the
                 * logic in this code block requires this, the assert
                 * is here to catch any instances where someone
                 * changes the logic to invalidate that assumption.
                 */
                KASSERT((n->m_flags & (M_EXT | M_PKTHDR)) == 0,
                        ("%s: Unexpected flags (%#x) for mbuf",
                        __func__, n->m_flags));
                n->m_data = n->m_dat + M_LEADINGSPACE_NOWRITE(m);
                n->m_len = m->m_len;
                if (m->m_flags & M_EXTPG)
                        m_copydata(m, 0, m->m_len, n->m_data);
                else
                        bcopy(M_START(m), n->m_dat,
                            m->m_len + M_LEADINGSPACE_NOWRITE(m));
        }
        else {
                /*
                 * This is the case where we need to "settle for what
                 * we can get". The most probable way to this code
                 * path is that we've already taken references to the
                 * maximum number of mbuf clusters we can, and the data
                 * is too long to fit in an mbuf's internal storage.
                 * Try for a "best fit".
                 */
                tcp_pcap_copy_bestfit(th, m, n);
 
                /* Don't try to get additional data. */
                goto add_to_queue;
        }
 
        if (m->m_next) {
                n->m_next = m_copym(m->m_next, 0, M_COPYALL, M_NOWAIT);
                tcp_pcap_adj_cluster_reference(n->m_next, 1);
        }
 
add_to_queue:
        /* Add the new mbuf to the list. */
        if (mbufq_enqueue(queue, n)) {
                /* This shouldn't happen. If INVARIANTS is defined, panic. */
                KASSERT(0, ("%s: mbufq was unexpectedly full!", __func__));
                tcp_pcap_m_freem(n);
        }
}
 
void
tcp_pcap_drain(struct mbufq *queue)
{
        struct mbuf *m;
        while ((m = mbufq_dequeue(queue)))
                tcp_pcap_m_freem(m);
}
 
void
tcp_pcap_tcpcb_init(struct tcpcb *tp)
{
        mbufq_init(&(tp->t_inpkts), V_tcp_pcap_packets);
        mbufq_init(&(tp->t_outpkts), V_tcp_pcap_packets);
}
 
void
tcp_pcap_set_sock_max(struct mbufq *queue, int newval)
{
        queue->mq_maxlen = newval;
        while (queue->mq_len > queue->mq_maxlen)
                tcp_pcap_m_freem(mbufq_dequeue(queue));
}
 
int
tcp_pcap_get_sock_max(struct mbufq *queue)
{
        return queue->mq_maxlen;
}