xnu-7195.81.3.tar.gz

[apple/xnu.git] / bsd / kern / uipc_mbuf2.c

/*
 * Copyright (c) 2000-2018 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*      $NetBSD: uipc_mbuf.c,v 1.40 1999/04/01 00:23:25 thorpej Exp $   */

/*
 * Copyright (C) 1999 WIDE Project.
 * 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.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE PROJECT 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 PROJECT 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.
 */

/*
 * Copyright (c) 1982, 1986, 1988, 1991, 1993
 *      The Regents of the University of California.  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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *      @(#)uipc_mbuf.c 8.4 (Berkeley) 2/14/95
 */
/*
 * NOTICE: This file was modified by SPARTA, Inc. in 2005 to introduce
 * support for mandatory and extensible security protections.  This notice
 * is included in support of clause 2.2 (b) of the Apple Public License,
 * Version 2.0.
 */


/*#define PULLDOWN_DEBUG*/

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc_internal.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/mcache.h>
#include <netinet/in.h>
#include <netinet/ip_var.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>

/*
 * ensure that [off, off + len) is contiguous on the mbuf chain "m".
 * packet chain before "off" is kept untouched.
 * if offp == NULL, the target will start at <retval, 0> on resulting chain.
 * if offp != NULL, the target will start at <retval, *offp> on resulting chain.
 *
 * on error return (NULL return value), original "m" will be freed.
 *
 * XXX M_TRAILINGSPACE/M_LEADINGSPACE on shared cluster (sharedcluster)
 */
struct mbuf *
m_pulldown(struct mbuf *m, int off, int len, int *offp)
{
        struct mbuf *n = NULL, *o = NULL;
        int hlen = 0, tlen = 0, olen = 0;
        int sharedcluster = 0;

        /* check invalid arguments. */
        VERIFY(len >= 0 && off >= 0);

        if (m == NULL) {
                panic("m == NULL in m_pulldown()");
        }
        if (len > MCLBYTES) {
                m_freem(m);
                return NULL;    /* impossible */
        }
        int tmp_len = 0;
        if (os_add_overflow(off, len, &tmp_len)) {
                m_free(m);
                return NULL;
        }

#ifdef PULLDOWN_DEBUG
        {
                struct mbuf *t;
                printf("before:");
                for (t = m; t; t = t->m_next) {
                        printf(" %d", t->m_len);
                }
                printf("\n");
        }
#endif
        n = m;

        /*
         * Iterate and make n point to the mbuf
         * within which the first byte at length
         * offset is contained from the start of
         * mbuf chain.
         */
        while (n != NULL && off > 0) {
                if (n->m_len > off) {
                        break;
                }
                off -= n->m_len;
                n = n->m_next;
        }

        /* be sure to point non-empty mbuf */
        while (n != NULL && n->m_len == 0) {
                n = n->m_next;
        }

        if (!n) {
                m_freem(m);
                return NULL;    /* mbuf chain too short */
        }

        /*
         * the target data is on <n, off>.
         * if we got enough data on the mbuf "n", we're done.
         *
         * It should be noted, that we should only do this either
         * when offset is 0, i.e. data is pointing to the start
         * or when the caller specifies an out argument to get
         * the offset value in the mbuf to work with data pointer
         * correctly.
         *
         * If offset is not 0 and caller did not provide out-argument
         * to get offset, we should split the mbuf even when the length
         * is contained in current mbuf.
         */
        if ((off == 0 || offp) && len <= n->m_len - off) {
                goto ok;
        }

        /*
         * when len <= n->m_len - off and off != 0, it is a special case.
         * len bytes from <n, off> sits in single mbuf, but the caller does
         * not like the starting position (off).
         * chop the current mbuf into two pieces, set off to 0.
         */
        if (len <= n->m_len - off) {
                o = m_copym(n, off, n->m_len - off, M_DONTWAIT);
                if (o == NULL) {
                        m_freem(m);
                        return NULL;    /* ENOBUFS */
                }
                n->m_len = off;
                o->m_next = n->m_next;
                n->m_next = o;
                n = n->m_next;
                off = 0;
                goto ok;
        }

        /*
         * we need to take hlen from <n, off> and tlen from <n->m_next, 0>,
         * and construct contiguous mbuf with m_len == len.
         * note that hlen + tlen == len, and tlen > 0.
         *
         * Read these variables as head length and tail length
         */
        hlen = n->m_len - off;
        tlen = len - hlen;

        /*
         * ensure that we have enough trailing data on mbuf chain.
         * if not, we can do nothing about the chain.
         */
        olen = 0;
        for (o = n->m_next; o != NULL; o = o->m_next) {
                olen += o->m_len;
        }
        if (hlen + olen < len) {
                m_freem(m);
                return NULL;    /* mbuf chain too short */
        }

        /*
         * easy cases first.
         * we need to use m_copydata() to get data from <n->m_next, 0>.
         */
        if ((n->m_flags & M_EXT) == 0) {
                sharedcluster = 0;
        } else {
                if (m_get_ext_free(n) != NULL) {
                        sharedcluster = 1;
                } else if (m_mclhasreference(n)) {
                        sharedcluster = 1;
                } else {
                        sharedcluster = 0;
                }
        }

        /*
         * If we have enough space left in current mbuf to accomodate
         * tail length, copy tail length worth of data starting with next mbuf
         * and adjust the length of next one accordingly.
         */
        if ((off == 0 || offp) && M_TRAILINGSPACE(n) >= tlen
            && !sharedcluster) {
                m_copydata(n->m_next, 0, tlen, mtod(n, caddr_t) + n->m_len);
                n->m_len += tlen;
                m_adj(n->m_next, tlen);
                goto ok;
        }

        /*
         * If have enough leading space in next mbuf to accomodate head length
         * of current mbuf, and total resulting length of next mbuf is greater
         * than or equal to requested len bytes, then just copy hlen from
         * current to the next one and adjust sizes accordingly.
         */
        if ((off == 0 || offp) && M_LEADINGSPACE(n->m_next) >= hlen &&
            (n->m_next->m_len + hlen) >= len && !sharedcluster) {
                n->m_next->m_data -= hlen;
                n->m_next->m_len += hlen;
                bcopy(mtod(n, caddr_t) + off, mtod(n->m_next, caddr_t), hlen);
                n->m_len -= hlen;
                n = n->m_next;
                off = 0;
                goto ok;
        }

        /*
         * now, we need to do the hard way.  don't m_copy as there's no room
         * on both end.
         */
        MGET(o, M_DONTWAIT, m->m_type);
        if (o == NULL) {
                m_freem(m);
                return NULL;    /* ENOBUFS */
        }
        if (len > MHLEN) {      /* use MHLEN just for safety */
                MCLGET(o, M_DONTWAIT);
                if ((o->m_flags & M_EXT) == 0) {
                        m_freem(m);
                        m_free(o);
                        return NULL;    /* ENOBUFS */
                }
        }
        /* get hlen from <n, off> into <o, 0> */
        o->m_len = hlen;
        bcopy(mtod(n, caddr_t) + off, mtod(o, caddr_t), hlen);
        n->m_len -= hlen;
        /* get tlen from <n->m_next, 0> into <o, hlen> */
        m_copydata(n->m_next, 0, tlen, mtod(o, caddr_t) + o->m_len);
        o->m_len += tlen;
        m_adj(n->m_next, tlen);
        o->m_next = n->m_next;
        n->m_next = o;
        n = o;
        off = 0;

ok:
#ifdef PULLDOWN_DEBUG
        {
                struct mbuf *t;
                printf("after:");
                for (t = m; t; t = t->m_next) {
                        printf("%c%d", t == n ? '*' : ' ', t->m_len);
                }
                printf(" (off=%d)\n", off);
        }
#endif
        if (offp) {
                *offp = off;
        }
        return n;
}

/*
 * Create and return an m_tag, either by re-using space in a previous tag
 * or by allocating a new mbuf/cluster
 */
struct m_tag *
m_tag_create(u_int32_t id, u_int16_t type, int len, int wait, struct mbuf *buf)
{
        struct m_tag *t = NULL;
        struct m_tag *p;

        if (len < 0) {
                return NULL;
        }

        if (len + sizeof(struct m_tag) + sizeof(struct m_taghdr) > MLEN) {
                return m_tag_alloc(id, type, len, wait);
        }

        /*
         * We've exhausted all external cases. Now, go through the m_tag
         * chain and see if we can fit it in any of them.
         * If not (t == NULL), call m_tag_alloc to store it in a new mbuf.
         */
        p = SLIST_FIRST(&buf->m_pkthdr.tags);
        while (p != NULL) {
                /* 2KCL m_tag */
                if (M_TAG_ALIGN(p->m_tag_len) +
                    sizeof(struct m_taghdr) > MLEN) {
                        p = SLIST_NEXT(p, m_tag_link);
                        continue;
                }

                VERIFY(p->m_tag_cookie == M_TAG_VALID_PATTERN);

                struct mbuf *m = m_dtom(p);
                struct m_taghdr *hdr = (struct m_taghdr *)(void *)m->m_data;

                VERIFY(IS_P2ALIGNED(hdr + 1, sizeof(u_int64_t)));
                VERIFY(m->m_flags & M_TAGHDR && !(m->m_flags & M_EXT));

                /* The mbuf can store this m_tag */
                if (M_TAG_ALIGN(len) <= MLEN - m->m_len) {
                        t = (struct m_tag *)(void *)(m->m_data + m->m_len);
                        VERIFY(IS_P2ALIGNED(t, sizeof(u_int64_t)));
                        hdr->refcnt++;
                        m->m_len += M_TAG_ALIGN(len);
                        VERIFY(m->m_len <= MLEN);
                        break;
                }

                p = SLIST_NEXT(p, m_tag_link);
        }

        if (t == NULL) {
                return m_tag_alloc(id, type, len, wait);
        }

        t->m_tag_cookie = M_TAG_VALID_PATTERN;
        t->m_tag_type = type;
        t->m_tag_len = (uint16_t)len;
        t->m_tag_id = id;
        if (len > 0) {
                bzero(t + 1, len);
        }
        return t;
}

/* Get a packet tag structure along with specified data following. */
struct m_tag *
m_tag_alloc(u_int32_t id, u_int16_t type, int len, int wait)
{
        struct m_tag *t;

        if (len < 0) {
                return NULL;
        }

        if (M_TAG_ALIGN(len) + sizeof(struct m_taghdr) <= MLEN) {
                struct mbuf *m = m_get(wait, MT_TAG);
                struct m_taghdr *hdr;

                if (m == NULL) {
                        return NULL;
                }

                m->m_flags |= M_TAGHDR;

                hdr = (struct m_taghdr *)(void *)m->m_data;
                VERIFY(IS_P2ALIGNED(hdr + 1, sizeof(u_int64_t)));
                hdr->refcnt = 1;
                m->m_len += sizeof(struct m_taghdr);
                t = (struct m_tag *)(void *)(m->m_data + m->m_len);
                VERIFY(IS_P2ALIGNED(t, sizeof(u_int64_t)));
                m->m_len += M_TAG_ALIGN(len);
                VERIFY(m->m_len <= MLEN);
        } else if (len + sizeof(struct m_tag) <= MCLBYTES) {
                t = (struct m_tag *)(void *)m_mclalloc(wait);
        } else {
                t = NULL;
        }

        if (t == NULL) {
                return NULL;
        }

        VERIFY(IS_P2ALIGNED(t, sizeof(u_int64_t)));
        t->m_tag_cookie = M_TAG_VALID_PATTERN;
        t->m_tag_type = type;
        t->m_tag_len = (uint16_t)len;
        t->m_tag_id = id;
        if (len > 0) {
                bzero(t + 1, len);
        }
        return t;
}


/* Free a packet tag. */
void
m_tag_free(struct m_tag *t)
{
        if (t == NULL) {
                return;
        }

        VERIFY(t->m_tag_cookie == M_TAG_VALID_PATTERN);

        if (M_TAG_ALIGN(t->m_tag_len) + sizeof(struct m_taghdr) <= MLEN) {
                struct mbuf * m = m_dtom(t);
                VERIFY(m->m_flags & M_TAGHDR);
                struct m_taghdr *hdr = (struct m_taghdr *)(void *)m->m_data;

                VERIFY(IS_P2ALIGNED(hdr + 1, sizeof(u_int64_t)));

                /* No other tags in this mbuf */
                if (--hdr->refcnt == 0) {
                        m_free(m);
                        return;
                }

                /* Pattern-fill the header */
                u_int64_t *fill_ptr = (u_int64_t *)t;
                u_int64_t *end_ptr = (u_int64_t *)(t + 1);
                while (fill_ptr < end_ptr) {
                        *fill_ptr = M_TAG_FREE_PATTERN;
                        fill_ptr++;
                }
        } else {
                m_mclfree((caddr_t)t);
        }
}

/* Prepend a packet tag. */
void
m_tag_prepend(struct mbuf *m, struct m_tag *t)
{
        VERIFY(m != NULL && t != NULL);

        SLIST_INSERT_HEAD(&m->m_pkthdr.tags, t, m_tag_link);
}

/* Unlink a packet tag. */
void
m_tag_unlink(struct mbuf *m, struct m_tag *t)
{
        VERIFY(m->m_flags & M_PKTHDR);
        VERIFY(t != NULL && t->m_tag_cookie == M_TAG_VALID_PATTERN);

        SLIST_REMOVE(&m->m_pkthdr.tags, t, m_tag, m_tag_link);
}

/* Unlink and free a packet tag. */
void
m_tag_delete(struct mbuf *m, struct m_tag *t)
{
        m_tag_unlink(m, t);
        m_tag_free(t);
}

/* Unlink and free a packet tag chain, starting from given tag. */
void
m_tag_delete_chain(struct mbuf *m, struct m_tag *t)
{
        struct m_tag *p, *q;

        VERIFY(m->m_flags & M_PKTHDR);

        if (t != NULL) {
                p = t;
        } else {
                p = SLIST_FIRST(&m->m_pkthdr.tags);
        }
        if (p == NULL) {
                return;
        }

        VERIFY(p->m_tag_cookie == M_TAG_VALID_PATTERN);
        while ((q = SLIST_NEXT(p, m_tag_link)) != NULL) {
                VERIFY(q->m_tag_cookie == M_TAG_VALID_PATTERN);
                m_tag_delete(m, q);
        }
        m_tag_delete(m, p);
}

/* Find a tag, starting from a given position. */
struct m_tag *
m_tag_locate(struct mbuf *m, u_int32_t id, u_int16_t type, struct m_tag *t)
{
        struct m_tag *p;

        VERIFY(m->m_flags & M_PKTHDR);

        if (t == NULL) {
                p = SLIST_FIRST(&m->m_pkthdr.tags);
        } else {
                VERIFY(t->m_tag_cookie == M_TAG_VALID_PATTERN);
                p = SLIST_NEXT(t, m_tag_link);
        }
        while (p != NULL) {
                VERIFY(p->m_tag_cookie == M_TAG_VALID_PATTERN);
                if (p->m_tag_id == id && p->m_tag_type == type) {
                        return p;
                }
                p = SLIST_NEXT(p, m_tag_link);
        }
        return NULL;
}

/* Copy a single tag. */
struct m_tag *
m_tag_copy(struct m_tag *t, int how)
{
        struct m_tag *p;

        VERIFY(t != NULL);

        p = m_tag_alloc(t->m_tag_id, t->m_tag_type, t->m_tag_len, how);
        if (p == NULL) {
                return NULL;
        }
        bcopy(t + 1, p + 1, t->m_tag_len); /* Copy the data */
        return p;
}

/*
 * Copy two tag chains. The destination mbuf (to) loses any attached
 * tags even if the operation fails. This should not be a problem, as
 * m_tag_copy_chain() is typically called with a newly-allocated
 * destination mbuf.
 */
int
m_tag_copy_chain(struct mbuf *to, struct mbuf *from, int how)
{
        struct m_tag *p, *t, *tprev = NULL;

        VERIFY((to->m_flags & M_PKTHDR) && (from->m_flags & M_PKTHDR));

        m_tag_delete_chain(to, NULL);
        SLIST_FOREACH(p, &from->m_pkthdr.tags, m_tag_link) {
                VERIFY(p->m_tag_cookie == M_TAG_VALID_PATTERN);
                t = m_tag_copy(p, how);
                if (t == NULL) {
                        m_tag_delete_chain(to, NULL);
                        return 0;
                }
                if (tprev == NULL) {
                        SLIST_INSERT_HEAD(&to->m_pkthdr.tags, t, m_tag_link);
                } else {
                        SLIST_INSERT_AFTER(tprev, t, m_tag_link);
                        tprev = t;
                }
        }
        return 1;
}

/* Initialize dynamic and static tags on an mbuf. */
void
m_tag_init(struct mbuf *m, int all)
{
        VERIFY(m->m_flags & M_PKTHDR);

        SLIST_INIT(&m->m_pkthdr.tags);
        /*
         * If the caller wants to preserve static mbuf tags
         * (e.g. m_dup_pkthdr), don't zero them out.
         */
        if (all) {
                bzero(&m->m_pkthdr.builtin_mtag._net_mtag,
                    sizeof(m->m_pkthdr.builtin_mtag._net_mtag));
        }
}

/* Get first tag in chain. */
struct m_tag *
m_tag_first(struct mbuf *m)
{
        VERIFY(m->m_flags & M_PKTHDR);

        return SLIST_FIRST(&m->m_pkthdr.tags);
}

/* Get next tag in chain. */
struct m_tag *
m_tag_next(struct mbuf *m, struct m_tag *t)
{
#pragma unused(m)
        VERIFY(t != NULL);
        VERIFY(t->m_tag_cookie == M_TAG_VALID_PATTERN);

        return SLIST_NEXT(t, m_tag_link);
}

int
m_set_traffic_class(struct mbuf *m, mbuf_traffic_class_t tc)
{
        u_int32_t val = MBUF_TC2SCVAL(tc);      /* just the val portion */

        return m_set_service_class(m, m_service_class_from_val(val));
}

mbuf_traffic_class_t
m_get_traffic_class(struct mbuf *m)
{
        return MBUF_SC2TC(m_get_service_class(m));
}

int
m_set_service_class(struct mbuf *m, mbuf_svc_class_t sc)
{
        int error = 0;

        VERIFY(m->m_flags & M_PKTHDR);

        if (MBUF_VALID_SC(sc)) {
                m->m_pkthdr.pkt_svc = sc;
        } else {
                error = EINVAL;
        }

        return error;
}

mbuf_svc_class_t
m_get_service_class(struct mbuf *m)
{
        mbuf_svc_class_t sc;

        VERIFY(m->m_flags & M_PKTHDR);

        if (MBUF_VALID_SC(m->m_pkthdr.pkt_svc)) {
                sc = m->m_pkthdr.pkt_svc;
        } else {
                sc = MBUF_SC_BE;
        }

        return sc;
}

mbuf_svc_class_t
m_service_class_from_idx(u_int32_t i)
{
        mbuf_svc_class_t sc = MBUF_SC_BE;

        switch (i) {
        case SCIDX_BK_SYS:
                return MBUF_SC_BK_SYS;

        case SCIDX_BK:
                return MBUF_SC_BK;

        case SCIDX_BE:
                return MBUF_SC_BE;

        case SCIDX_RD:
                return MBUF_SC_RD;

        case SCIDX_OAM:
                return MBUF_SC_OAM;

        case SCIDX_AV:
                return MBUF_SC_AV;

        case SCIDX_RV:
                return MBUF_SC_RV;

        case SCIDX_VI:
                return MBUF_SC_VI;

        case SCIDX_VO:
                return MBUF_SC_VO;

        case SCIDX_CTL:
                return MBUF_SC_CTL;

        default:
                break;
        }

        VERIFY(0);
        /* NOTREACHED */
        return sc;
}

mbuf_svc_class_t
m_service_class_from_val(u_int32_t v)
{
        mbuf_svc_class_t sc = MBUF_SC_BE;

        switch (v) {
        case SCVAL_BK_SYS:
                return MBUF_SC_BK_SYS;

        case SCVAL_BK:
                return MBUF_SC_BK;

        case SCVAL_BE:
                return MBUF_SC_BE;

        case SCVAL_RD:
                return MBUF_SC_RD;

        case SCVAL_OAM:
                return MBUF_SC_OAM;

        case SCVAL_AV:
                return MBUF_SC_AV;

        case SCVAL_RV:
                return MBUF_SC_RV;

        case SCVAL_VI:
                return MBUF_SC_VI;

        case SCVAL_VO:
                return MBUF_SC_VO;

        case SCVAL_CTL:
                return MBUF_SC_CTL;

        default:
                break;
        }

        VERIFY(0);
        /* NOTREACHED */
        return sc;
}

uint16_t
m_adj_sum16(struct mbuf *m, uint32_t start, uint32_t dataoff,
    uint32_t datalen, uint32_t sum)
{
        uint32_t total_sub = 0;                 /* total to subtract */
        uint32_t mlen = m_pktlen(m);            /* frame length */
        uint32_t bytes = (dataoff + datalen);   /* bytes covered by sum */
        int len;

        ASSERT(bytes <= mlen);

        /*
         * Take care of excluding (len > 0) or including (len < 0)
         * extraneous octets at the beginning of the packet, taking
         * into account the start offset.
         */
        len = (dataoff - start);
        if (len > 0) {
                total_sub = m_sum16(m, start, len);
        } else if (len < 0) {
                sum += m_sum16(m, dataoff, -len);
        }

        /*
         * Take care of excluding any postpended extraneous octets.
         */
        len = (mlen - bytes);
        if (len > 0) {
                struct mbuf *m0 = m;
                uint32_t extra = m_sum16(m, bytes, len);
                uint32_t off = bytes, off0 = off;

                while (off > 0) {
                        if (__improbable(m == NULL)) {
                                panic("%s: invalid mbuf chain %p [off %u, "
                                    "len %u]", __func__, m0, off0, len);
                                /* NOTREACHED */
                        }
                        if (off < m->m_len) {
                                break;
                        }
                        off -= m->m_len;
                        m = m->m_next;
                }

                /* if we started on odd-alignment, swap the value */
                if ((uintptr_t)(mtod(m, uint8_t *) + off) & 1) {
                        total_sub += ((extra << 8) & 0xffff) | (extra >> 8);
                } else {
                        total_sub += extra;
                }

                total_sub = (total_sub >> 16) + (total_sub & 0xffff);
        }

        /*
         * 1's complement subtract any extraneous octets.
         */
        if (total_sub != 0) {
                if (total_sub >= sum) {
                        sum = ~(total_sub - sum) & 0xffff;
                } else {
                        sum -= total_sub;
                }
        }

        /* fold 32-bit to 16-bit */
        sum = (sum >> 16) + (sum & 0xffff);     /* 17-bit */
        sum = (sum >> 16) + (sum & 0xffff);     /* 16-bit + carry */
        sum = (sum >> 16) + (sum & 0xffff);     /* final carry */

        return sum & 0xffff;
}

uint16_t
m_sum16(struct mbuf *m, uint32_t off, uint32_t len)
{
        int mlen;

        /*
         * Sanity check
         *
         * Use m_length2() instead of m_length(), as we cannot rely on
         * the caller setting m_pkthdr.len correctly, if the mbuf is
         * a M_PKTHDR one.
         */
        if ((mlen = m_length2(m, NULL)) < (off + len)) {
                panic("%s: mbuf %p len (%d) < off+len (%d+%d)\n", __func__,
                    m, mlen, off, len);
                /* NOTREACHED */
        }

        return (uint16_t)os_cpu_in_cksum_mbuf(m, len, off, 0);
}