mbuf.c

一个Windows下的Linux专用虚拟机

/*
 * 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;
int mbuf_thresh = 30;
int mbuf_max = 0;
int msize;

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

void
msize_init()
{
	/*
	 * Find a nice value for msize
	 * XXX if_maxlinkhdr already in mtu
	 */
	msize = (if_mtu>if_mru?if_mtu:if_mru) + 
			if_maxlinkhdr + sizeof(struct m_hdr ) + 6;
}

/*
 * 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;
{
	char *dat;
	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;
	  dat = (char *)realloc(m->m_ext,size);
/*		if (dat == NULL)
 *			return (struct mbuf *)NULL;
 */		
        } else {
	  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_flags |= M_EXT;
        }
 
	m->m_ext = dat;
	m->m_data = m->m_ext + datasize;
        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;
}