/*
 * Copyright (c) 1995 Danny Gasparovski
 *
 * Please read the file COPYRIGHT for the
 * terms and conditions of the copyright.
 */

/*
 * mbuf's in SLiRP are much simpler than the real mbufs in
 * FreeBSD.  They are fixed size, determined by the MTU,
 * so that one whole packet can fit.  Mbuf's cannot be
 * chained together.  If there's more data than the mbuf
 * could hold, an external malloced buffer is pointed to
 * by m_ext (and the data pointers) and M_EXT is set in
 * the flags
 */

#include <slirp.h>

static int mbuf_alloced;
struct mbuf m_freelist, m_usedlist;
#define MBUF_THRESH 30

/*
 * Find a nice value for msize
 * XXX if_maxlinkhdr already in mtu
 */
#define SLIRP_MSIZE (IF_MTU + IF_MAXLINKHDR + sizeof(struct m_hdr) + 6)

void m_init(void)
{
    m_freelist.m_next = m_freelist.m_prev = &m_freelist;
    m_usedlist.m_next = m_usedlist.m_prev = &m_usedlist;
}

/*
 * Get an mbuf from the free list, if there are none
 * malloc one
 *
 * Because fragmentation can occur if we alloc new mbufs and
 * free old mbufs, we mark all mbufs above mbuf_thresh as M_DOFREE,
 * which tells m_free to actually free() it
 */
struct mbuf *m_get(void)
{
    register struct mbuf *m;
    int flags = 0;

    DEBUG_CALL("m_get");

    if (m_freelist.m_next == &m_freelist) {
        m = (struct mbuf *)malloc(SLIRP_MSIZE);
        if (m == NULL)
            goto end_error;
        mbuf_alloced++;
        if (mbuf_alloced > MBUF_THRESH)
            flags = M_DOFREE;
    } else {
        m = m_freelist.m_next;
        remque(m);
    }

    /* Insert it in the used list */
    insque(m, &m_usedlist);
    m->m_flags = (flags | M_USEDLIST);

    /* Initialise it */
    m->m_size = SLIRP_MSIZE - sizeof(struct m_hdr);
    m->m_data = m->m_dat;
    m->m_len = 0;
    m->m_nextpkt = NULL;
    m->m_prevpkt = NULL;
end_error:
    DEBUG_ARG("m = %lx", (long)m);
    return m;
}

void m_free(struct mbuf *m)
{
    DEBUG_CALL("m_free");
    DEBUG_ARG("m = %lx", (long)m);

    if (m) {
        /* Remove from m_usedlist */
        if (m->m_flags & M_USEDLIST)
            remque(m);

        /* If it's M_EXT, free() it */
        if (m->m_flags & M_EXT)
            free(m->m_ext);

        /*
         * Either free() it or put it on the free list
         */
        if (m->m_flags & M_DOFREE) {
            free(m);
            mbuf_alloced--;
        } else if ((m->m_flags & M_FREELIST) == 0) {
            insque(m, &m_freelist);
            m->m_flags = M_FREELIST; /* Clobber other flags */
        }
    } /* if(m) */
}

/*
 * Copy data from one mbuf to the end of
 * the other.. if result is too big for one mbuf, malloc()
 * an M_EXT data segment
 */
void m_cat(struct mbuf *m, struct mbuf *n)
{
    /*
     * If there's no room, realloc
     */
    if (M_FREEROOM(m) < n->m_len)
        m_inc(m, m->m_size + MINCSIZE);

    memcpy(m->m_data + m->m_len, n->m_data, n->m_len);
    m->m_len += n->m_len;

    m_free(n);
}


/* make m size bytes large */
void m_inc(struct mbuf *m, int size)
{
    int datasize;

    /* some compiles throw up on gotos.  This one we can fake. */
    if (m->m_size > size)
        return;

    if (m->m_flags & M_EXT) {
        datasize = m->m_data - m->m_ext;
        m->m_ext = (char *)realloc(m->m_ext, size);
        m->m_data = m->m_ext + datasize;
    } else {
        char *dat;
        datasize = m->m_data - m->m_dat;
        dat = (char *)malloc(size);
        memcpy(dat, m->m_dat, m->m_size);

        m->m_ext = dat;
        m->m_data = m->m_ext + datasize;
        m->m_flags |= M_EXT;
    }

    m->m_size = size;
}


void m_adj(struct mbuf *m, int len)
{
    if (m == NULL)
        return;
    if (len >= 0) {
        /* Trim from head */
        m->m_data += len;
        m->m_len -= len;
    } else {
        /* Trim from tail */
        len = -len;
        m->m_len -= len;
    }
}


/*
 * Copy len bytes from m, starting off bytes into n
 */
int m_copy(struct mbuf *n, struct mbuf *m, int off, int len)
{
    if (len > M_FREEROOM(n))
        return -1;

    memcpy((n->m_data + n->m_len), (m->m_data + off), len);
    n->m_len += len;
    return 0;
}


/*
 * Given a pointer into an mbuf, return the mbuf
 * XXX This is a kludge, I should eliminate the need for it
 * Fortunately, it's not used often
 */
struct mbuf *dtom(void *dat)
{
    struct mbuf *m;

    DEBUG_CALL("dtom");
    DEBUG_ARG("dat = %lx", (long)dat);

    /* bug corrected for M_EXT buffers */
    for (m = m_usedlist.m_next; m != &m_usedlist; m = m->m_next) {
        if (m->m_flags & M_EXT) {
            if ((char *)dat >= m->m_ext && (char *)dat < (m->m_ext + m->m_size))
                return m;
        } else {
            if ((char *)dat >= m->m_dat && (char *)dat < (m->m_dat + m->m_size))
                return m;
        }
    }

    DEBUG_ERROR((dfd, "dtom failed"));

    return (struct mbuf *)0;
}