fsys.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

	}
}

static void
hold(Plumbmsg *m, Dirtab *d)
{
	Holdq *h, *q;

	h = emalloc(sizeof(Holdq));
	h->msg = m;
	/* add to end of queue */
	if(d->holdq == nil)
		d->holdq = h;
	else{
		for(q=d->holdq; q->next!=nil; q=q->next)
			;
		q->next = h;
	}
}

static void
queueheld(Dirtab *d)
{
	Holdq *h;

	while(d->holdq != nil){
		h = d->holdq;
		d->holdq = h->next;
		queuesend(d, h->msg);
		/* no need to drain queue because we know no-one is reading yet */
		free(h);
	}
}

static void
dispose(Fcall *t, uchar *buf, Plumbmsg *m, Ruleset *rs, Exec *e)
{
	int i;
	char *err;

	qlock(&queue);
	err = nil;
	if(m->dst==nil || m->dst[0]=='\0'){
		err = Enoport;
		if(rs != nil)
			err = startup(rs, e);
		plumbfree(m);
	}else
		for(i=NQID; i<ndir; i++)
			if(strcmp(m->dst, dir[i].name) == 0){
				if(dir[i].nopen == 0){
					err = startup(rs, e);
					if(e!=nil && e->holdforclient)
						hold(m, &dir[i]);
					else
						plumbfree(m);
				}else{
					queuesend(&dir[i], m);
					drainqueue(&dir[i]);
				}
				break;
			}
	freeexec(e);
	qunlock(&queue);
	fsysrespond(t, buf, err);
	free(t);
}

static Fcall*
fsysversion(Fcall *t, uchar *buf, Fid*)
{
	if(t->msize < 256){
		fsysrespond(t, buf, "version: message size too small");
		return t;
	}
	if(t->msize < messagesize)
		messagesize = t->msize;
	t->msize = messagesize;
	if(strncmp(t->version, "9P2000", 6) != 0){
		fsysrespond(t, buf, "unrecognized 9P version");
		return t;
	}
	t->version = "9P2000";
	fsysrespond(t, buf, nil);
	return t;
}

static Fcall*
fsysauth(Fcall *t, uchar *buf, Fid*)
{
	fsysrespond(t, buf, "plumber: authentication not required");
	return t;
}

static Fcall*
fsysattach(Fcall *t, uchar *buf, Fid *f)
{
	Fcall out;

	if(strcmp(t->uname, user) != 0){
		fsysrespond(&out, buf, Eperm);
		return t;
	}
	f->busy = 1;
	f->open = 0;
	f->qid.type = QTDIR;
	f->qid.path = Qdir;
	f->qid.vers = 0;
	f->dir = dir;
	memset(&out, 0, sizeof(Fcall));
	out.type = t->type;
	out.tag = t->tag;
	out.fid = f->fid;
	out.qid = f->qid;
	fsysrespond(&out, buf, nil);
	return t;
}

static Fcall*
fsysflush(Fcall *t, uchar *buf, Fid*)
{
	int i;

	qlock(&queue);
	for(i=NQID; i<ndir; i++)
		flushqueue(&dir[i], t->oldtag);
	qunlock(&queue);
	fsysrespond(t, buf, nil);
	return t;
}

static Fcall*
fsyswalk(Fcall *t, uchar *buf, Fid *f)
{
	Fcall out;
	Fid *nf;
	ulong path;
	Dirtab *d, *dir;
	Qid q;
	int i;
	uchar type;
	char *err;

	if(f->open){
		fsysrespond(t, buf, "clone of an open fid");
		return t;
	}

	nf = nil;
	if(t->fid  != t->newfid){
		nf = newfid(t->newfid);
		if(nf->busy){
			fsysrespond(t, buf, "clone to a busy fid");
			return t;
		}
		nf->busy = 1;
		nf->open = 0;
		nf->dir = f->dir;
		nf->qid = f->qid;
		f = nf;	/* walk f */
	}

	out.nwqid = 0;
	err = nil;
	dir = f->dir;
	q = f->qid;

	if(t->nwname > 0){
		for(i=0; i<t->nwname; i++){
			if((q.type & QTDIR) == 0){
				err = Enotdir;
				break;
			}
			if(strcmp(t->wname[i], "..") == 0){
				type = QTDIR;
				path = Qdir;
	Accept:
				q.type = type;
				q.vers = 0;
				q.path = path;
				out.wqid[out.nwqid++] = q;
				continue;
			}
			d = dir;
			d++;	/* skip '.' */
			for(; d->name; d++)
				if(strcmp(t->wname[i], d->name) == 0){
					type = d->type;
					path = d->qid;
					dir = d;
					goto Accept;
				}
			err = Enoexist;
			break;
		}
	}

	out.type = t->type;
	out.tag = t->tag;
	if(err!=nil || out.nwqid<t->nwname){
		if(nf)
			nf->busy = 0;
	}else if(out.nwqid == t->nwname){
		f->qid = q;
		f->dir = dir;
	}

	fsysrespond(&out, buf, err);
	return t;
}

static Fcall*
fsysopen(Fcall *t, uchar *buf, Fid *f)
{
	int m, clearrules, mode;

	clearrules = 0;
	if(t->mode & OTRUNC){
		if(f->qid.path != Qrules)
			goto Deny;
		clearrules = 1;
	}
	/* can't truncate anything, so just disregard */
	mode = t->mode & ~(OTRUNC|OCEXEC);
	/* can't execute or remove anything */
	if(mode==OEXEC || (mode&ORCLOSE))
		goto Deny;
	switch(mode){
	default:
		goto Deny;
	case OREAD:
		m = 0400;
		break;
	case OWRITE:
		m = 0200;
		break;
	case ORDWR:
		m = 0600;
		break;
	}
	if(((f->dir->perm&~(DMDIR|DMAPPEND))&m) != m)
		goto Deny;
	if(f->qid.path==Qrules && (mode==OWRITE || mode==ORDWR)){
		lock(&rulesref);
		if(rulesref.ref++ != 0){
			rulesref.ref--;
			unlock(&rulesref);
			fsysrespond(t, buf, Einuse);
			return t;
		}
		unlock(&rulesref);
	}
	if(clearrules){
		writerules(nil, 0);
		rules[0] = nil;
	}
	t->qid = f->qid;
	t->iounit = 0;
	qlock(&queue);
	f->mode = mode;
	f->open = 1;
	f->dir->nopen++;
	f->nextopen = f->dir->fopen;
	f->dir->fopen = f;
	queueheld(f->dir);
	qunlock(&queue);
	fsysrespond(t, buf, nil);
	return t;

    Deny:
	fsysrespond(t, buf, Eperm);
	return t;
}

static Fcall*
fsyscreate(Fcall *t, uchar *buf, Fid*)
{
	fsysrespond(t, buf, Eperm);
	return t;
}

static Fcall*
fsysreadrules(Fcall *t, uchar *buf)
{
	char *p;
	int n;

	p = printrules();
	n = strlen(p);
	t->data = p;
	if(t->offset >= n)
		t->count = 0;
	else{
		t->data = p+t->offset;
		if(t->offset+t->count > n)
			t->count = n-t->offset;
	}
	fsysrespond(t, buf, nil);
	free(p);
	return t;
}

static Fcall*
fsysread(Fcall *t, uchar *buf, Fid *f)
{
	uchar *b;
	int i, n, o, e;
	uint len;
	Dirtab *d;
	uint clock;

	if(f->qid.path != Qdir){
		if(f->qid.path == Qrules)
			return fsysreadrules(t, buf);
		/* read from port */
		if(f->qid.path < NQID){
			fsysrespond(t, buf, "internal error: unknown read port");
			return t;
		}
		qlock(&queue);
		queueread(f->dir, t, buf, f);
		drainqueue(f->dir);
		qunlock(&queue);
		return nil;
	}
	o = t->offset;
	e = t->offset+t->count;
	clock = getclock();
	b = malloc(messagesize-IOHDRSZ);
	if(b == nil){
		fsysrespond(t, buf, Enomem);
		return t;
	}
	n = 0;
	d = dir;
	d++;	/* first entry is '.' */
	for(i=0; d->name!=nil && i<e; i+=len){
		len = dostat(d, b+n, messagesize-IOHDRSZ-n, clock);
		if(len <= BIT16SZ)
			break;
		if(i >= o)
			n += len;
		d++;
	}
	t->data = (char*)b;
	t->count = n;
	fsysrespond(t, buf, nil);
	free(b);
	return t;
}

static Fcall*
fsyswrite(Fcall *t, uchar *buf, Fid *f)
{
	Plumbmsg *m;
	int i, n;
	long count;
	char *data;
	Exec *e;

	switch((int)f->qid.path){
	case Qdir:
		fsysrespond(t, buf, Eisdir);
		return t;
	case Qrules:
		clock = getclock();
		fsysrespond(t, buf, writerules(t->data, t->count));
		return t;
	case Qsend:
		if(f->offset == 0){
			data = t->data;
			count = t->count;
		}else{
			/* partial message already assembled */
			f->writebuf = erealloc(f->writebuf, f->offset + t->count);
			memmove(f->writebuf+f->offset, t->data, t->count);
			data = f->writebuf;
			count = f->offset+t->count;
		}
		m = plumbunpackpartial(data, count, &n);
		if(m == nil){
			if(n == 0){
				f->offset = 0;
				free(f->writebuf);
				f->writebuf = nil;
				fsysrespond(t, buf, Ebadmsg);
				return t;
			}
			/* can read more... */
			if(f->offset == 0){
				f->writebuf = emalloc(t->count);
				memmove(f->writebuf, t->data, t->count);
			}
			/* else buffer has already been grown */
			f->offset += t->count;
			fsysrespond(t, buf, nil);
			return t;
		}
		/* release partial buffer */
		f->offset = 0;
		free(f->writebuf);
		f->writebuf = nil;
		for(i=0; rules[i]; i++)
			if((e=matchruleset(m, rules[i])) != nil){
				dispose(t, buf, m, rules[i], e);
				return nil;
			}
		if(m->dst != nil){
			dispose(t, buf, m, nil, nil);
			return nil;
		}
		fsysrespond(t, buf, "no matching plumb rule");
		return t;
	}
	fsysrespond(t, buf, "internal error: write to unknown file");
	return t;
}

static Fcall*
fsysstat(Fcall *t, uchar *buf, Fid *f)
{
	t->stat = emalloc(messagesize-IOHDRSZ);
	t->nstat = dostat(f->dir, t->stat, messagesize-IOHDRSZ, clock);
	fsysrespond(t, buf, nil);
	free(t->stat);
	t->stat = nil;
	return t;
}

static Fcall*
fsyswstat(Fcall *t, uchar *buf, Fid*)
{
	fsysrespond(t, buf, Eperm);
	return t;
}

static Fcall*
fsysremove(Fcall *t, uchar *buf, Fid*)
{
	fsysrespond(t, buf, Eperm);
	return t;
}

static Fcall*
fsysclunk(Fcall *t, uchar *buf, Fid *f)
{
	Fid *prev, *p;
	Dirtab *d;

	qlock(&queue);
	if(f->open){
		d = f->dir;
		d->nopen--;
		if(d->qid==Qrules && (f->mode==OWRITE || f->mode==ORDWR)){
			/*
			 * just to be sure last rule is parsed; error messages will be lost, though,
			 * unless last write ended with a blank line
			 */
			writerules(nil, 0);
			lock(&rulesref);
			rulesref.ref--;
			unlock(&rulesref);
		}
		prev = nil;
		for(p=d->fopen; p; p=p->nextopen){
			if(p == f){
				if(prev)
					prev->nextopen = f->nextopen;
				else
					d->fopen = f->nextopen;
				removesenders(d, f);
				break;
			}
			prev = p;
		}
	}
	f->busy = 0;
	f->open = 0;
	f->offset = 0;
	if(f->writebuf != nil){
		free(f->writebuf);
		f->writebuf = nil;
	}
	qunlock(&queue);
	fsysrespond(t, buf, nil);
	return t;
}