chan.c

在x86平台上运行不可信任代码的sandbox。

	if(a->dev != b->dev)
		return 0;
	return 1;
}

int
eqchantdqid(Chan *a, int type, int dev, Qid qid, int skipvers)
{
	if(a->qid.path != qid.path)
		return 0;
	if(!skipvers && a->qid.vers!=qid.vers)
		return 0;
	if(a->type != type)
		return 0;
	if(a->dev != dev)
		return 0;
	return 1;
}

Mhead*
newmhead(Chan *from)
{
	Mhead *mh;

	mh = smalloc(sizeof(Mhead));
	mh->ref.ref = 1;
	mh->from = from;
	incref(&from->ref);
	return mh;
}

int
cmount(Chan **newp, Chan *old, int flag, char *spec)
{
	int order, flg;
	Chan *new;
	Mhead *m, **l, *mh;
	Mount *nm, *f, *um, **h;
	Pgrp *pg;

	if(QTDIR & (old->qid.type^(*newp)->qid.type))
		error(Emount);

	if(old->umh)
		print("cmount: unexpected umh, caller %.8lux\n", getcallerpc(&newp));

	order = flag&MORDER;

	if((old->qid.type&QTDIR)==0 && order != MREPL)
		error(Emount);

	new = *newp;
	mh = new->umh;

	/*
	 * Not allowed to bind when the old directory is itself a union. 
	 * (Maybe it should be allowed, but I don't see what the semantics
	 * would be.)
	 *
	 * We need to check mh->mount->next to tell unions apart from
	 * simple mount points, so that things like
	 *	mount -c fd /root
	 *	bind -c /root /
	 * work.  
	 * 
	 * The check of mount->mflag allows things like
	 *	mount fd /root
	 *	bind -c /root /
	 * 
	 * This is far more complicated than it should be, but I don't
	 * see an easier way at the moment.
	 */
	if((flag&MCREATE) && mh && mh->mount
	&& (mh->mount->next || !(mh->mount->mflag&MCREATE)))
		error(Emount);

	pg = up->pgrp;
	wlock(&pg->ns);

	l = &MOUNTH(pg, old->qid);
	for(m = *l; m; m = m->hash){
		if(eqchan(m->from, old, 1))
			break;
		l = &m->hash;
	}

	if(m == nil){
		/*
		 *  nothing mounted here yet.  create a mount
		 *  head and add to the hash table.
		 */
		m = newmhead(old);
		*l = m;

		/*
		 *  if this is a union mount, add the old
		 *  node to the mount chain.
		 */
		if(order != MREPL)
			m->mount = newmount(m, old, 0, 0);
	}
	wlock(&m->lock);
	if(waserror()){
		wunlock(&m->lock);
		nexterror();
	}
	wunlock(&pg->ns);

	nm = newmount(m, new, flag, spec);
	if(mh != nil && mh->mount != nil){
		/*
		 *  copy a union when binding it onto a directory
		 */
		flg = order;
		if(order == MREPL)
			flg = MAFTER;
		h = &nm->next;
		um = mh->mount;
		for(um = um->next; um; um = um->next){
			f = newmount(m, um->to, flg, um->spec);
			*h = f;
			h = &f->next;
		}
	}

	if(m->mount && order == MREPL){
		mountfree(m->mount);
		m->mount = 0;
	}

	if(flag & MCREATE)
		nm->mflag |= MCREATE;

	if(m->mount && order == MAFTER){
		for(f = m->mount; f->next; f = f->next)
			;
		f->next = nm;
	}else{
		for(f = nm; f->next; f = f->next)
			;
		f->next = m->mount;
		m->mount = nm;
	}

	wunlock(&m->lock);
	poperror();
	return nm->mountid;
}

void
cunmount(Chan *mnt, Chan *mounted)
{
	Pgrp *pg;
	Mhead *m, **l;
	Mount *f, **p;

	if(mnt->umh)	/* should not happen */
		print("cunmount newp extra umh %p has %p\n", mnt, mnt->umh);

	/*
	 * It _can_ happen that mounted->umh is non-nil, 
	 * because mounted is the result of namec(Aopen)
	 * (see sysfile.c:/^sysunmount).
	 * If we open a union directory, it will have a umh.
	 * Although surprising, this is okay, since the
	 * cclose will take care of freeing the umh.
	 */

	pg = up->pgrp;
	wlock(&pg->ns);

	l = &MOUNTH(pg, mnt->qid);
	for(m = *l; m; m = m->hash){
		if(eqchan(m->from, mnt, 1))
			break;
		l = &m->hash;
	}

	if(m == 0){
		wunlock(&pg->ns);
		error(Eunmount);
	}

	wlock(&m->lock);
	if(mounted == 0){
		*l = m->hash;
		wunlock(&pg->ns);
		mountfree(m->mount);
		m->mount = nil;
		cclose(m->from);
		wunlock(&m->lock);
		putmhead(m);
		return;
	}

	p = &m->mount;
	for(f = *p; f; f = f->next){
		/* BUG: Needs to be 2 pass */
		if(eqchan(f->to, mounted, 1) ||
		  (f->to->mchan && eqchan(f->to->mchan, mounted, 1))){
			*p = f->next;
			f->next = 0;
			mountfree(f);
			if(m->mount == nil){
				*l = m->hash;
				cclose(m->from);
				wunlock(&m->lock);
				wunlock(&pg->ns);
				putmhead(m);
				return;
			}
			wunlock(&m->lock);
			wunlock(&pg->ns);
			return;
		}
		p = &f->next;
	}
	wunlock(&m->lock);
	wunlock(&pg->ns);
	error(Eunion);
}

Chan*
cclone(Chan *c)
{
	Chan *nc;
	Walkqid *wq;

	wq = devtab[c->type]->walk(c, nil, nil, 0);
	if(wq == nil)
		error("clone failed");
	nc = wq->clone;
	free(wq);
	nc->path = c->path;
	if(c->path)
		incref(&c->path->ref);
	return nc;
}

/* also used by sysfile.c:/^mountfix */
int
findmount(Chan **cp, Mhead **mp, int type, int dev, Qid qid)
{
	Pgrp *pg;
	Mhead *m;

	pg = up->pgrp;
	rlock(&pg->ns);
	for(m = MOUNTH(pg, qid); m; m = m->hash){
		rlock(&m->lock);
		if(m->from == nil){
			print("m %p m->from 0\n", m);
			runlock(&m->lock);
			continue;
		}
		if(eqchantdqid(m->from, type, dev, qid, 1)){
			runlock(&pg->ns);
			if(mp != nil){
				incref(&m->ref);
				if(*mp != nil)
					putmhead(*mp);
				*mp = m;
			}
			if(*cp != nil)
				cclose(*cp);
			incref(&m->mount->to->ref);
			*cp = m->mount->to;
			runlock(&m->lock);
			return 1;
		}
		runlock(&m->lock);
	}

	runlock(&pg->ns);
	return 0;
}

/*
 * Calls findmount but also updates path.
 */
static int
domount(Chan **cp, Mhead **mp, Path **path)
{
	Chan **lc;
	Path *p;

	if(findmount(cp, mp, (*cp)->type, (*cp)->dev, (*cp)->qid) == 0)
		return 0;

	if(path){
		p = *path;
		p = uniquepath(p);
		if(p->mlen <= 0)
			print("domount: path %s has mlen==%d\n", p->s, p->mlen);
		else{
			lc = &p->mtpt[p->mlen-1];
DBG("domount %p %s => add %p (was %p)\n", p, p->s, (*mp)->from, p->mtpt[p->mlen-1]);
			incref(&(*mp)->from->ref);
			if(*lc)
				cclose(*lc);
			*lc = (*mp)->from;
		}
		*path = p;
	}
	return 1;
}

/*
 * If c is the right-hand-side of a mount point, returns the left hand side.
 * Changes name to reflect the fact that we've uncrossed the mountpoint,
 * so name had better be ours to change!
 */
static Chan*
undomount(Chan *c, Path *path)
{
	Chan *nc;

	if(path->ref.ref != 1 || path->mlen == 0)
		print("undomount: path %s ref %ld mlen %d caller %lux\n",
			path->s, path->ref.ref, path->mlen, getcallerpc(&c));

	if(path->mlen>0 && (nc=path->mtpt[path->mlen-1]) != nil){
DBG("undomount %p %s => remove %p\n", path, path->s, nc);
		cclose(c);
		path->mtpt[path->mlen-1] = nil;
		c = nc;
	}
	return c;
}

/*
 * Call dev walk but catch errors.
 */
static Walkqid*
ewalk(Chan *c, Chan *nc, char **name, int nname)
{
	Walkqid *wq;

	if(waserror())
		return nil;
	wq = devtab[c->type]->walk(c, nc, name, nname);
	poperror();
	return wq;
}

/*
 * Either walks all the way or not at all.  No partial results in *cp.
 * *nerror is the number of names to display in an error message.
 */
static char Edoesnotexist[] = "does not exist";
int
walk(Chan **cp, char **names, int nnames, int nomount, int *nerror)
{
	int dev, didmount, dotdot, i, n, nhave, ntry, type;
	Chan *c, *nc, *mtpt;
	Path *path;
	Mhead *mh, *nmh;
	Mount *f;
	Walkqid *wq;

	c = *cp;
	incref(&c->ref);
	path = c->path;
	incref(&path->ref);
	mh = nil;

	/*
	 * While we haven't gotten all the way down the path:
	 *    1. step through a mount point, if any
	 *    2. send a walk request for initial dotdot or initial prefix without dotdot
	 *    3. move to the first mountpoint along the way.
	 *    4. repeat.
	 *
	 * Each time through the loop:
	 *
	 *	If didmount==0, c is on the undomount side of the mount point.
	 *	If didmount==1, c is on the domount side of the mount point.
	 * 	Either way, c's full path is path.
	 */
	didmount = 0;
	for(nhave=0; nhave<nnames; nhave+=n){
		if((c->qid.type&QTDIR)==0){
			if(nerror)
				*nerror = nhave;
			pathclose(path);
			cclose(c);
			strcpy(up->errstr, Enotdir);
			if(mh != nil)
				putmhead(mh);
			return -1;
		}
		ntry = nnames - nhave;
		if(ntry > MAXWELEM)
			ntry = MAXWELEM;
		dotdot = 0;
		for(i=0; i<ntry; i++){
			if(isdotdot(names[nhave+i])){
				if(i==0){
					dotdot = 1;
					ntry = 1;
				}else
					ntry = i;
				break;
			}
		}

		if(!dotdot && !nomount && !didmount)
			domount(&c, &mh, &path);
		
		type = c->type;
		dev = c->dev;

		if((wq = ewalk(c, nil, names+nhave, ntry)) == nil){
			/* try a union mount, if any */
			if(mh && !nomount){
				/*
				 * mh->mount->to == c, so start at mh->mount->next
				 */
				rlock(&mh->lock);
				for(f = mh->mount->next; f; f = f->next)
					if((wq = ewalk(f->to, nil, names+nhave, ntry)) != nil)
						break;
				runlock(&mh->lock);
				if(f != nil){
					type = f->to->type;
					dev = f->to->dev;
				}
			}
			if(wq == nil){
				cclose(c);
				pathclose(path);
				if(nerror)
					*nerror = nhave+1;
				if(mh != nil)
					putmhead(mh);
				return -1;
			}
		}

		didmount = 0;
		if(dotdot){
			assert(wq->nqid == 1);
			assert(wq->clone != nil);

			path = addelem(path, "..", nil);
			nc = undomount(wq->clone, path);
			nmh = nil;
			n = 1;
		}else{
			nc = nil;
			nmh = nil;
			if(!nomount){
				for(i=0; i<wq->nqid && i<ntry-1; i++){
					if(findmount(&nc, &nmh, type, dev, wq->qid[i])){
						didmount = 1;
						break;
					}
				}
			}
			if(nc == nil){	/* no mount points along path */
				if(wq->clone == nil){
					cclose(c);
					pathclose(path);
					if(wq->nqid==0 || (wq->qid[wq->nqid-1].type&QTDIR)){
						if(nerror)
							*nerror = nhave+wq->nqid+1;
						strcpy(up->errstr, Edoesnotexist);
					}else{
						if(nerror)
							*nerror = nhave+wq->nqid;
						strcpy(up->errstr, Enotdir);
					}
					free(wq);
					if(mh != nil)
						putmhead(mh);
					return -1;
				}
				n = wq->nqid;
				nc = wq->clone;
			}else{		/* stopped early, at a mount point */
				didmount = 1;
				if(wq->clone != nil){
					cclose(wq->clone);
					wq->clone = nil;
				}
				n = i+1;
			}
			for(i=0; i<n; i++){
				mtpt = nil;
				if(i==n-1 && nmh)
					mtpt = nmh->from;
				path = addelem(path, names[nhave+i], mtpt);
			}
		}
		cclose(c);
		c = nc;
		putmhead(mh);
		mh = nmh;
		free(wq);
	}

	putmhead(mh);

	c = cunique(c);

	if(c->umh != nil){	//BUG
		print("walk umh\n");
		putmhead(c->umh);
		c->umh = nil;
	}

	pathclose(c->path);
	c->path = path;

	cclose(*cp);
	*cp = c;
	if(nerror)
		*nerror = nhave;
	return 0;
}

/*
 * c is a mounted non-creatable directory.  find a creatable one.
 */
Chan*
createdir(Chan *c, Mhead *m)
{
	Chan *nc;
	Mount *f;

	rlock(&m->lock);
	if(waserror()){
		runlock(&m->lock);
		nexterror();
	}
	for(f = m->mount; f; f = f->next){
		if(f->mflag&MCREATE){
			nc = cclone(f->to);
			runlock(&m->lock);
			poperror();
			cclose(c);
			return nc;
		}
	}
	error(Enocreate);
	return 0;
}

void
saveregisters(void)
{
}

static void
growparse(Elemlist *e)
{
	char **new;
	int *inew;
	enum { Delta = 8 };

	if(e->nelems % Delta == 0){
		new = smalloc((e->nelems+Delta) * sizeof(char*));
		memmove(new, e->elems, e->nelems*sizeof(char*));
		free(e->elems);
		e->elems = new;
		inew = smalloc((e->nelems+Delta+1) * sizeof(int));
		memmove(inew, e->off, (e->nelems+1)*sizeof(int));
		free(e->off);
		e->off = inew;
	}
}

/*
 * The name is known to be valid.
 * Copy the name so slashes can be overwritten.
 * An empty string will set nelem=0.
 * A path ending in / or /. or /.//./ etc. will have
 * e.mustbedir = 1, so that we correctly
 * reject, e.g., "/adm/users/." when /adm/users is a file
 * rather than a directory.
 */
static void
parsename(char *aname, Elemlist *e)
{
	char *name, *slash;

	kstrdup(&e->name, aname);
	name = e->name;
	e->nelems = 0;
	e->elems = nil;
	e->off = smalloc(sizeof(int));
	e->off[0] = skipslash(name) - name;
	for(;;){
		name = skipslash(name);
		if(*name == '\0'){