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mbuf.c

/*
 * 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>

struct      mbuf *mbutl;
char  *mclrefcnt;
int mbuf_alloced = 0;
struct mbuf m_freelist, m_usedlist;
#define MBUF_THRESH 30
int mbuf_max = 0;

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

void
m_init()
{
      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()
{
      register struct mbuf *m;
      int flags = 0;

      DEBUG_CALL("m_get");

      if (m_freelist.m_next == &m_freelist) {
            m = (struct mbuf *)malloc(MSIZE);
            if (m == NULL) goto end_error;
            mbuf_alloced++;
            if (mbuf_alloced > MBUF_THRESH)
                  flags = M_DOFREE;
            if (mbuf_alloced > mbuf_max)
                  mbuf_max = mbuf_alloced;
      } 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 = MSIZE - sizeof(struct m_hdr);
      m->m_data = m->m_dat;
      m->m_len = 0;
      m->m_nextpkt = 0;
      m->m_prevpkt = 0;
end_error:
      DEBUG_ARG("m = %lx", (long )m);
      return m;
}

void
m_free(m)
      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(m, n)
      register struct mbuf *m, *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(m, size)
        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);
/*          if (m->m_ext == NULL)
 *                return (struct mbuf *)NULL;
 */
        m->m_data = m->m_ext + datasize;
        } else {
        char *dat;
        datasize = m->m_data - m->m_dat;
        dat = (char *)malloc(size);
/*          if (dat == NULL)
 *                return (struct mbuf *)NULL;
 */
        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(m, len)
      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(n, m, off, len)
      struct mbuf *n, *m;
      int off, 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(dat)
      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;
}


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