main.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include <u.h>
#include <libc.h>
#include <ip.h>
#include <bio.h>
#include <fcall.h>
#include <libsec.h>
#include "dat.h"
#include "protos.h"
#include "y.tab.h"

int Cflag;
int pflag;
int Nflag;
int Mflag;
int sflag;
int tiflag;
int toflag;

char *prom = "promiscuous";

enum
{
	Pktlen=	64*1024,
	Blen=	16*1024,
};

Filter *filter;
Proto *root;
Biobuf out;
vlong starttime, pkttime;
int pcap;

int	filterpkt(Filter *f, uchar *ps, uchar *pe, Proto *pr, int);
void	printpkt(char *p, char *e, uchar *ps, uchar *pe);
void	mkprotograph(void);
Proto*	findproto(char *name);
Filter*	compile(Filter *f);
void	printfilter(Filter *f, char *tag);
void	printhelp(char*);
void	tracepkt(uchar*, int);
void	pcaphdr(void);

void
printusage(void)
{
	fprint(2, "usage: %s [-CDdpst] [-N n] [-f filter] [-h first-header] path\n", argv0);
	fprint(2, "  for protocol help: %s -? [proto]\n", argv0);
}

void
usage(void)
{
	printusage();
	exits("usage");
}

void
main(int argc, char **argv)
{
	uchar *pkt;
	char *buf, *file, *p, *e;
	int fd, cfd;
	int n;

	Binit(&out, 1, OWRITE);

	fmtinstall('E', eipfmt);
	fmtinstall('V', eipfmt);
	fmtinstall('I', eipfmt);
	fmtinstall('H', encodefmt);
	fmtinstall('F', fcallfmt);

	pkt = malloc(Pktlen+16);
	pkt += 16;
	buf = malloc(Blen);
	e = buf+Blen-1;

	pflag = 1;
	Nflag = 32;
	sflag = 0;

	mkprotograph();

	ARGBEGIN{
	default:
		usage();
	case '?':
		printusage();
		printhelp(ARGF());
		exits(0);
		break;
	case 'M':
		p = EARGF(usage());
		Mflag = atoi(p);
		break;
	case 'N':
		p = EARGF(usage());
		Nflag = atoi(p);
		break;
	case 'f':
		p = EARGF(usage());
		yyinit(p);
		yyparse();
		break;
	case 's':
		sflag = 1;
		break;
	case 'h':
		p = EARGF(usage());
		root = findproto(p);
		if(root == nil)
			sysfatal("unknown protocol: %s", p);
		break;
	case 'd':
		toflag = 1;
		break;
	case 'D':
		toflag = 1;
		pcap = 1;
		break;
	case 't':
		tiflag = 1;
		break;
	case 'C':
		Cflag = 1;
		break;
	case 'p':
		pflag = 0;
		break;
	}ARGEND;

	if(pcap)
		pcaphdr();

	if(argc == 0){
		file = "/net/ether0";
		if(root != nil)
			root = &ether;
	} else
		file = argv[0];

	if((!tiflag) && strstr(file, "ether")){
		if(root == nil)
			root = &ether;
		snprint(buf, Blen, "%s!-1", file);
		fd = dial(buf, 0, 0, &cfd);
		if(fd < 0)
			sysfatal("dialing %s", buf);
		if(pflag && fprint(cfd, prom, strlen(prom)) < 0)
			sysfatal("setting %s", prom);
	} else if((!tiflag) && strstr(file, "ipifc")){
		if(root == nil)
			root = &ip;
		snprint(buf, Blen, "%s/snoop", file);
		fd = open(buf, OREAD);
		if(fd < 0)
			sysfatal("opening %s: %r", buf);
	} else {
		if(root == nil)
			root = &ether;
		fd = open(file, OREAD);
		if(fd < 0)
			sysfatal("opening %s: %r", file);
	}
	filter = compile(filter);

	if(tiflag){
		/* read a trace file */
		for(;;){
			n = read(fd, pkt, 10);
			if(n != 10)
				break;
			pkttime = NetL(pkt+2);
			pkttime = (pkttime<<32) | NetL(pkt+6);
			if(starttime == 0LL)
				starttime = pkttime;
			n = NetS(pkt);
			if(readn(fd, pkt, n) != n)
				break;
			if(filterpkt(filter, pkt, pkt+n, root, 1))
				if(toflag)
					tracepkt(pkt, n);
				else
					printpkt(buf, e, pkt, pkt+n);
		}
	} else {
		/* read a real time stream */
		starttime = nsec();
		for(;;){
			n = root->framer(fd, pkt, Pktlen);
			if(n <= 0)
				break;
			pkttime = nsec();
			if(filterpkt(filter, pkt, pkt+n, root, 1))
				if(toflag)
					tracepkt(pkt, n);
				else
					printpkt(buf, e, pkt, pkt+n);
		}
	}
}

/* create a new filter node */
Filter*
newfilter(void)
{
	Filter *f;

	f = mallocz(sizeof(*f), 1);
	if(f == nil)
		sysfatal("newfilter: %r");
	return f;
}

/*
 *  apply filter to packet
 */
int
_filterpkt(Filter *f, Msg *m)
{
	Msg ma;

	if(f == nil)
		return 1;

	switch(f->op){
	case '!':
		return !_filterpkt(f->l, m);
	case LAND:
		ma = *m;
		return _filterpkt(f->l, &ma) && _filterpkt(f->r, m);
	case LOR:
		ma = *m;
		return _filterpkt(f->l, &ma) || _filterpkt(f->r, m);
	case WORD:
		if(m->needroot){
			if(m->pr != f->pr)
				return 0;
			m->needroot = 0;
		}else{
			if(m->pr && (m->pr->filter==nil || !(m->pr->filter)(f, m)))
				return 0;
		}
		if(f->l == nil)
			return 1;
		m->pr = f->pr;
		return _filterpkt(f->l, m);
	}
	sysfatal("internal error: filterpkt op: %d", f->op);
	return 0;
}
int
filterpkt(Filter *f, uchar *ps, uchar *pe, Proto *pr, int needroot)
{
	Msg m;

	if(f == nil)
		return 1;

	m.needroot = needroot;
	m.ps = ps;
	m.pe = pe;
	m.pr = pr;
	return _filterpkt(f, &m);
}

/*
 *  from the Unix world
 */
#define PCAP_VERSION_MAJOR 2
#define PCAP_VERSION_MINOR 4
#define TCPDUMP_MAGIC 0xa1b2c3d4

struct pcap_file_header {
	ulong		magic;
	ushort		version_major;
	ushort		version_minor;
	long		thiszone;    /* gmt to local correction */
	ulong		sigfigs;    /* accuracy of timestamps */
	ulong		snaplen;    /* max length saved portion of each pkt */
	ulong		linktype;   /* data link type (DLT_*) */
};

struct pcap_pkthdr {
        uvlong	ts;	/* time stamp */
        ulong	caplen;	/* length of portion present */
        ulong	len;	/* length this packet (off wire) */
};

/*
 *  pcap trace header 
 */
void
pcaphdr(void)
{
	struct pcap_file_header hdr;

	hdr.magic = TCPDUMP_MAGIC;
	hdr.version_major = PCAP_VERSION_MAJOR;
	hdr.version_minor = PCAP_VERSION_MINOR;
  
	hdr.thiszone = 0;
	hdr.snaplen = 1500;
	hdr.sigfigs = 0;
	hdr.linktype = 1;

	write(1, &hdr, sizeof(hdr));
}

/*
 *  write out a packet trace
 */
void
tracepkt(uchar *ps, int len)
{
	struct pcap_pkthdr *goo;

	if(Mflag && len > Mflag)
		len = Mflag;
	if(pcap){
		goo = (struct pcap_pkthdr*)(ps-16);
		goo->ts = pkttime;
		goo->caplen = len;
		goo->len = len;
		write(1, goo, len+16);
	} else {
		hnputs(ps-10, len);
		hnputl(ps-8, pkttime>>32);
		hnputl(ps-4, pkttime);
		write(1, ps-10, len+10);
	}
}

/*
 *  format and print a packet
 */
void
printpkt(char *p, char *e, uchar *ps, uchar *pe)
{
	Msg m;
	ulong dt;

	dt = (pkttime-starttime)/1000000LL;
	m.p = seprint(p, e, "%6.6uld ms ", dt);
	m.ps = ps;
	m.pe = pe;
	m.e = e;
	m.pr = root;
	while(m.p < m.e){
		if(!sflag)
			m.p = seprint(m.p, m.e, "\n\t");
		m.p = seprint(m.p, m.e, "%s(", m.pr->name);
		if((*m.pr->seprint)(&m) < 0){
			m.p = seprint(m.p, m.e, "TOO SHORT");
			m.ps = m.pe;
		}
		m.p = seprint(m.p, m.e, ")");
		if(m.pr == nil || m.ps >= m.pe)
			break;
	}
	*m.p++ = '\n';

	if(write(1, p, m.p - p) < 0)
		sysfatal("stdout: %r");
}

Proto **xprotos;
int nprotos;

/* look up a protocol by its name */
Proto*
findproto(char *name)
{
	int i;

	for(i = 0; i < nprotos; i++)
		if(strcmp(xprotos[i]->name, name) == 0)
			return xprotos[i];
	return nil;
}

/*
 *  add an undefined protocol to protos[]
 */
Proto*
addproto(char *name)
{
	Proto *pr;

	xprotos = realloc(xprotos, (nprotos+1)*sizeof(Proto*));
	pr = malloc(sizeof *pr);
	*pr = dump;
	pr->name = name;
	xprotos[nprotos++] = pr;
	return pr;
}

/*
 *  build a graph of protocols, this could easily be circular.  This
 *  links together all the multiplexing in the protocol modules.
 */
void
mkprotograph(void)
{
	Proto **l;
	Proto *pr;
	Mux *m;

	/* copy protos into a reallocable area */
	for(nprotos = 0; protos[nprotos] != nil; nprotos++)
		;
	xprotos = malloc(nprotos*sizeof(Proto*));
	memmove(xprotos, protos, nprotos*sizeof(Proto*));

	for(l = protos; *l != nil; l++){
		pr = *l;
		for(m = pr->mux; m != nil && m->name != nil; m++){
			m->pr = findproto(m->name);
			if(m->pr == nil)
				m->pr = addproto(m->name);
		}
	}
}

/*
 *  add in a protocol node
 */
static Filter*
addnode(Filter *f, Proto *pr)
{
	Filter *nf;
	nf = newfilter();
	nf->pr = pr;
	nf->s = pr->name;
	nf->l = f;
	nf->op = WORD;
	return nf;
}

/*
 *  recurse through the protocol graph adding missing nodes
 *  to the filter if we reach the filter's protocol
 */
static Filter*
_fillin(Filter *f, Proto *last, int depth)
{
	Mux *m;
	Filter *nf;

	if(depth-- <= 0)
		return nil;

	for(m = last->mux; m != nil && m->name != nil; m++){
		if(m->pr == nil)
			continue;
		if(f->pr == m->pr)
			return f;
		nf = _fillin(f, m->pr, depth);
		if(nf != nil)
			return addnode(nf, m->pr);
	}
	return nil;
}

static Filter*
fillin(Filter *f, Proto *last)
{
	int i;
	Filter *nf;

	/* hack to make sure top level node is the root */