fs.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

		pos += m;
	}
	return n;
}

int
readmboxdir(Fid *f, uchar *buf, long off, int cnt, int blen)
{
	Dir d;
	int n, m;
	long pos;
	Message *msg;

	n = 0;
	if(f->mb->ctl){
		mkstat(&d, f->mb, nil, Qmboxctl);
		m = convD2M(&d, &buf[n], blen);
		if(off == 0){
			if(m <= BIT16SZ || m > cnt){
				f->fptr = nil;
				return 0;
			}
			n += m;
			cnt -= m;
		} else
			off -= m;
	}

	// to avoid n**2 reads of the directory, use a saved finger pointer
	if(f->mb->vers == f->fvers && off >= f->foff && f->fptr != nil){
		msg = f->fptr;
		pos = f->foff;
	} else {
		msg = f->mb->root->part;
		pos = 0;
	} 

	for(; cnt > 0 && msg != nil; msg = msg->next){
		// act like deleted files aren't there
		if(msg->deleted)
			continue;

		mkstat(&d, f->mb, msg, Qdir);
		m = convD2M(&d, &buf[n], blen-n);
		if(off <= pos){
			if(m <= BIT16SZ || m > cnt)
				break;
			n += m;
			cnt -= m;
		}
		pos += m;
	}

	// save a finger pointer for next read of the mbox directory
	f->foff = pos;
	f->fptr = msg;
	f->fvers = f->mb->vers;

	return n;
}

int
readmsgdir(Fid *f, uchar *buf, long off, int cnt, int blen)
{
	Dir d;
	int i, n, m;
	long pos;
	Message *msg;

	n = 0;
	pos = 0;
	for(i = 0; i < Qmax; i++){
		mkstat(&d, f->mb, f->m, i);
		m = convD2M(&d, &buf[n], blen-n);
		if(off <= pos){
			if(m <= BIT16SZ || m > cnt)
				return n;
			n += m;
			cnt -= m;
		}
		pos += m;
	}
	for(msg = f->m->part; msg != nil; msg = msg->next){
		mkstat(&d, f->mb, msg, Qdir);
		m = convD2M(&d, &buf[n], blen-n);
		if(off <= pos){
			if(m <= BIT16SZ || m > cnt)
				break;
			n += m;
			cnt -= m;
		}
		pos += m;
	}

	return n;
}

char*
rread(Fid *f)
{
	long off;
	int t, i, n, cnt;
	char *p;

	rhdr.count = 0;
	off = thdr.offset;
	cnt = thdr.count;

	if(cnt > messagesize - IOHDRSZ)
		cnt = messagesize - IOHDRSZ;

	rhdr.data = (char*)mbuf;

	t = FILE(f->qid.path);
	if(f->qid.type & QTDIR){
		if(t == Qtop) {
			qlock(&mbllock);
			n = readtopdir(f, mbuf, off, cnt, messagesize - IOHDRSZ);
			qunlock(&mbllock);
		} else if(t == Qmbox) {
			qlock(f->mb);
			if(off == 0)
				syncmbox(f->mb, 1);
			n = readmboxdir(f, mbuf, off, cnt, messagesize - IOHDRSZ);
			qunlock(f->mb);
		} else if(t == Qmboxctl) {
			n = 0;
		} else {
			n = readmsgdir(f, mbuf, off, cnt, messagesize - IOHDRSZ);
		}

		rhdr.count = n;
		return nil;
	}

	if(FILE(f->qid.path) == Qheader){
		rhdr.count = readheader(f->m, (char*)mbuf, off, cnt);
		return nil;
	}

	if(FILE(f->qid.path) == Qinfo){
		rhdr.count = readinfo(f->m, (char*)mbuf, off, cnt);
		return nil;
	}

	i = fileinfo(f->m, FILE(f->qid.path), &p);
	if(off < i){
		if((off + cnt) > i)
			cnt = i - off;
		memmove(mbuf, p + off, cnt);
		rhdr.count = cnt;
	}
	return nil;
}

char*
rwrite(Fid *f)
{
	char *err;
	char *token[1024];
	int t, n;
	String *file;

	t = FILE(f->qid.path);
	rhdr.count = thdr.count;
	switch(t){
	case Qctl:
		if(thdr.count == 0)
			return Ebadctl;
		if(thdr.data[thdr.count-1] == '\n')
			thdr.data[thdr.count-1] = 0;
		else
			thdr.data[thdr.count] = 0;
		n = tokenize(thdr.data, token, nelem(token));
		if(n == 0)
			return Ebadctl;
		if(strcmp(token[0], "open") == 0){
			file = s_new();
			switch(n){
			case 1:
				err = Ebadctl;
				break;
			case 2:
				mboxpath(token[1], getlog(), file, 0);
				err = newmbox(s_to_c(file), nil, 0);
				break;
			default:
				mboxpath(token[1], getlog(), file, 0);
				if(strchr(token[2], '/') != nil)
					err = "/ not allowed in mailbox name";
				else
					err = newmbox(s_to_c(file), token[2], 0);
				break;
			}
			s_free(file);
			return err;
		}
		if(strcmp(token[0], "close") == 0){
			if(n < 2)
				return nil;
			freembox(token[1]);
			return nil;
		}
		if(strcmp(token[0], "delete") == 0){
			if(n < 3)
				return nil;
			delmessages(n-1, &token[1]);
			return nil;
		}
		return Ebadctl;
	case Qmboxctl:
		if(f->mb && f->mb->ctl){
			if(thdr.count == 0)
				return Ebadctl;
			if(thdr.data[thdr.count-1] == '\n')
				thdr.data[thdr.count-1] = 0;
			else
				thdr.data[thdr.count] = 0;
			n = tokenize(thdr.data, token, nelem(token));
			if(n == 0)
				return Ebadctl;
			return (*f->mb->ctl)(f->mb, n, token);
		}
	}
	return Eperm;
}

char *
rclunk(Fid *f)
{
	Mailbox *mb;

	f->busy = 0;
	f->open = 0;
	if(f->mtop != nil){
		qlock(f->mb);
		msgdecref(f->mb, f->mtop);
		qunlock(f->mb);
	}
	f->m = f->mtop = nil;
	mb = f->mb;
	if(mb != nil){
		f->mb = nil;
		assert(mb->refs > 0);
		qlock(&mbllock);
		mboxdecref(mb);
		qunlock(&mbllock);
	}
	f->fid = -1;
	return 0;
}

char *
rremove(Fid *f)
{
	if(f->m != nil){
		if(f->m->deleted == 0)
			mailplumb(f->mb, f->m, 1);
		f->m->deleted = 1;
	}
	return rclunk(f);
}

char *
rstat(Fid *f)
{
	Dir d;

	if(FILE(f->qid.path) == Qmbox){
		qlock(f->mb);
		syncmbox(f->mb, 1);
		qunlock(f->mb);
	}
	mkstat(&d, f->mb, f->m, FILE(f->qid.path));
	rhdr.nstat = convD2M(&d, mbuf, messagesize - IOHDRSZ);
	rhdr.stat = mbuf;
	return 0;
}

char *
rwstat(Fid*)
{
	return Eperm;
}

Fid *
newfid(int fid)
{
	Fid *f, *ff;

	ff = 0;
	for(f = fids; f; f = f->next)
		if(f->fid == fid)
			return f;
		else if(!ff && !f->busy)
			ff = f;
	if(ff){
		ff->fid = fid;
		ff->fptr = nil;
		return ff;
	}
	f = emalloc(sizeof *f);
	f->fid = fid;
	f->fptr = nil;
	f->next = fids;
	fids = f;
	return f;
}

int
fidmboxrefs(Mailbox *mb)
{
	Fid *f;
	int refs = 0;

	for(f = fids; f; f = f->next){
		if(f->mb == mb)
			refs++;
	}
	return refs;
}

void
io(void)
{
	char *err;
	int n;

	/* start a process to watch the mailboxes*/
	if(plumbing){
		switch(rfork(RFPROC|RFMEM)){
		case -1:
			/* oh well */
			break;
		case 0:
			reader();
			exits(nil);
		default:
			break;
		}
	}

	for(;;){
		/*
		 * reading from a pipe or a network device
		 * will give an error after a few eof reads
		 * however, we cannot tell the difference
		 * between a zero-length read and an interrupt
		 * on the processes writing to us,
		 * so we wait for the error
		 */
		checkmboxrefs();
		n = read9pmsg(mfd[0], mdata, messagesize);
		if(n == 0)
			continue;
		if(n < 0)
			return;
		if(convM2S(mdata, n, &thdr) == 0)
			continue;

		if(debug)
			fprint(2, "%s:<-%F\n", argv0, &thdr);

		rhdr.data = (char*)mdata + messagesize;
		if(!fcalls[thdr.type])
			err = "bad fcall type";
		else
			err = (*fcalls[thdr.type])(newfid(thdr.fid));
		if(err){
			rhdr.type = Rerror;
			rhdr.ename = err;
		}else{
			rhdr.type = thdr.type + 1;
			rhdr.fid = thdr.fid;
		}
		rhdr.tag = thdr.tag;
		if(debug)
			fprint(2, "%s:->%F\n", argv0, &rhdr);/**/
		n = convS2M(&rhdr, mdata, messagesize);
		if(write(mfd[1], mdata, n) != n)
			error("mount write");
	}
}

void
reader(void)
{
	ulong t;
	Dir *d;
	Mailbox *mb;

	sleep(15*1000);
	for(;;){
		t = time(0);
		qlock(&mbllock);
		for(mb = mbl; mb != nil; mb = mb->next){
			assert(mb->refs > 0);
			if(mb->waketime != 0 && t > mb->waketime){
				qlock(mb);
				mb->waketime = 0;
				break;
			}

			d = dirstat(mb->path);
			if(d == nil)
				continue;

			qlock(mb);
			if(mb->d)
			if(d->qid.path != mb->d->qid.path
			   || d->qid.vers != mb->d->qid.vers){
				free(d);
				break;
			}
			qunlock(mb);
			free(d);
		}
		qunlock(&mbllock);
		if(mb != nil){
			syncmbox(mb, 1);
			qunlock(mb);
		} else
			sleep(15*1000);
	}
}

int
newid(void)
{
	int rv;
	static int id;
	static Lock idlock;

	lock(&idlock);
	rv = ++id;
	unlock(&idlock);

	return rv;
}

void
error(char *s)
{
	postnote(PNGROUP, getpid(), "die yankee pig dog");
	fprint(2, "%s: %s: %r\n", argv0, s);
	exits(s);
}


typedef struct Ignorance Ignorance;
struct Ignorance
{
	Ignorance *next;
	char	*str;		/* string */
	int	partial;	/* true if not exact match */
};
Ignorance *ignorance;

/*
 *  read the file of headers to ignore 
 */
void
readignore(void)
{
	char *p;
	Ignorance *i;
	Biobuf *b;

	if(ignorance != nil)
		return;

	b = Bopen("/mail/lib/ignore", OREAD);
	if(b == 0)
		return;
	while(p = Brdline(b, '\n')){
		p[Blinelen(b)-1] = 0;
		while(*p && (*p == ' ' || *p == '\t'))
			p++;
		if(*p == '#')
			continue;
		i = malloc(sizeof(Ignorance));
		if(i == 0)
			break;
		i->partial = strlen(p);
		i->str = strdup(p);
		if(i->str == 0){
			free(i);
			break;
		}
		i->next = ignorance;
		ignorance = i;
	}
	Bterm(b);
}

int
ignore(char *p)
{
	Ignorance *i;

	readignore();
	for(i = ignorance; i != nil; i = i->next)
		if(cistrncmp(i->str, p, i->partial) == 0)
			return 1;
	return 0;
}

int
hdrlen(char *p, char *e)
{
	char *ep;

	ep = p;
	do {
		ep = strchr(ep, '\n');
		if(ep == nil){
			ep = e;
			break;
		}
		ep++;
		if(ep >= e){
			ep = e;
			break;
		}
	} while(*ep == ' ' || *ep == '\t');
	return ep - p;
}

// rfc2047 non-ascii: =?charset?q?encoded-text?=
int
rfc2047convert(String *s, char *token, int len)
{
	char charset[100], decoded[1024], *e, *x;
	int l;

	if(len == 0)
		return -1;

	e = token+len-2;
	token += 2;

	x = memchr(token, '?', e-token);
	if(x == nil || (l=x-token) >= sizeof charset)
		return -1;
	memmove(charset, token, l);
	charset[l] = 0;

	token = x+1;

	// bail if it doesn't fit 
	if(e-token > sizeof(decoded)-1)
		return -1;

	// bail if we don't understand the encoding
	if(cistrncmp(token, "b?", 2) == 0){
		token += 2;
		len = dec64((uchar*)decoded, sizeof(decoded), token, e-token);
		decoded[len] = 0;
	} else if(cistrncmp(token, "q?", 2) == 0){
		token += 2;
		len = decquoted(decoded, token, e, 1);
		if(len > 0 && decoded[len-1] == '\n')
			len--;
		decoded[len] = 0;
	} else
		return -1;

	if(xtoutf(charset, &x, decoded, decoded+len) <= 0)
		s_append(s, decoded);
	else {
		s_append(s, x);
		free(x);
	}
	return 0;
}

char*
rfc2047start(char *start, char *end)
{
	int quests;

	if(*--end != '=')
		return nil;
	if(*--end != '?')
		return nil;

	quests = 0;
	for(end--; end >= start; end--){
		switch(*end){
		case '=':
			if(quests == 3 && *(end+1) == '?')
				return end;
			break;
		case '?':
			++quests;
			break;
		case ' ':
		case '\t':
		case '\n':
		case '\r':
			/* can't have white space in a token */
			return nil;
		}
	}
	return nil;
}

// convert a header line
String*
stringconvert(String *s, char *uneaten, int len)
{
	char *token, *p, *e;

	s = s_reset(s);
	p = uneaten;
	for(e = p+len; p < e; ){
		while(*p++ == '=' && (token = rfc2047start(uneaten, p))){
			s_nappend(s, uneaten, token-uneaten);
			if(rfc2047convert(s, token, p - token) < 0)
				s_nappend(s, token, p - token);
			uneaten = p;
			for(; p<e && isspace(*p);)
				p++;
			if(p+2 < e && p[0] == '=' && p[1] == '?')
				uneaten = p;	// paste
		}
	}
	if(p > uneaten)
		s_nappend(s, uneaten, p-uneaten);
	return s;
}

int
readheader(Message *m, char *buf, int off, int cnt)
{
	char *p, *e;
	int n, ns;
	char *to = buf;
	String *s;

	p = m->header;
	e = m->hend;
	s = nil;

	// copy in good headers
	while(cnt > 0 && p < e){
		n = hdrlen(p, e);
		if(ignore(p)){
			p += n;
			continue;
		}

		// rfc2047 processing
		s = stringconvert(s, p, n);
		ns = s_len(s);
		if(off > 0){
			if(ns <= off){
				off -= ns;
				p += n;
				continue;
			}
			ns -= off;
		}
		if(ns > cnt)
			ns = cnt;
		memmove(to, s_to_c(s)+off, ns);
		to += ns;
		p += n;
		cnt -= ns;
		off = 0;
	}

	s_free(s);
	return to - buf;
}

int
headerlen(Message *m)
{
	char buf[1024];
	int i, n;

	if(m->hlen >= 0)
		return m->hlen;
	for(n = 0; ; n += i){
		i = readheader(m, buf, n, sizeof(buf));
		if(i <= 0)
			break;
	}
	m->hlen = n;
	return n;
}

QLock hashlock;

uint
hash(ulong ppath, char *name)
{
	uchar *p;
	uint h;

	h = 0;
	for(p = (uchar*)name; *p; p++)
		h = h*7 + *p;
	h += ppath;

	return h % Hsize;
}

Hash*
hlook(ulong ppath, char *name)
{
	int h;
	Hash *hp;

	qlock(&hashlock);
	h = hash(ppath, name);
	for(hp = htab[h]; hp != nil; hp = hp->next)
		if(ppath == hp->ppath && strcmp(name, hp->name) == 0){
			qunlock(&hashlock);
			return hp;
		}
	qunlock(&hashlock);
	return nil;
}

void
henter(ulong ppath, char *name, Qid qid, Message *m, Mailbox *mb)
{
	int h;
	Hash *hp, **l;

	qlock(&hashlock);
	h = hash(ppath, name);
	for(l = &htab[h]; *l != nil; l = &(*l)->next){
		hp = *l;
		if(ppath == hp->ppath && strcmp(name, hp->name) == 0){
			hp->m = m;
			hp->mb = mb;
			hp->qid = qid;
			qunlock(&hashlock);
			return;
		}
	}

	*l = hp = emalloc(sizeof(*hp));
	hp->m = m;
	hp->mb = mb;
	hp->qid = qid;
	hp->name = name;
	hp->ppath = ppath;
	qunlock(&hashlock);
}

void
hfree(ulong ppath, char *name)
{
	int h;
	Hash *hp, **l;

	qlock(&hashlock);
	h = hash(ppath, name);
	for(l = &htab[h]; *l != nil; l = &(*l)->next){
		hp = *l;
		if(ppath == hp->ppath && strcmp(name, hp->name) == 0){
			hp->mb = nil;
			*l = hp->next;
			free(hp);
			break;
		}
	}
	qunlock(&hashlock);
}

int
hashmboxrefs(Mailbox *mb)
{
	int h;
	Hash *hp;
	int refs = 0;

	qlock(&hashlock);
	for(h = 0; h < Hsize; h++){
		for(hp = htab[h]; hp != nil; hp = hp->next)
			if(hp->mb == mb)
				refs++;
	}
	qunlock(&hashlock);
	return refs;
}

void
checkmboxrefs(void)
{
	int f, refs;
	Mailbox *mb;

	qlock(&mbllock);
	for(mb=mbl; mb; mb=mb->next){
		qlock(mb);
		refs = (f=fidmboxrefs(mb))+1;
		if(refs != mb->refs){
			fprint(2, "mbox %s %s ref mismatch actual %d (%d+1) expected %d\n", mb->name, mb->path, refs, f, mb->refs);
			abort();
		}
		qunlock(mb);
	}
	qunlock(&mbllock);
}

void
post(char *name, char *envname, int srvfd)
{
	int fd;
	char buf[32];

	fd = create(name, OWRITE, 0600);
	if(fd < 0)
		error("post failed");
	sprint(buf, "%d",srvfd);
	if(write(fd, buf, strlen(buf)) != strlen(buf))
		error("srv write");
	close(fd);
	putenv(envname, name);
}