Subversion Repositories planix.SVN

Rev

Rev 2 | Details | Compare with Previous | Last modification | View Log | RSS feed

Rev Author Line No. Line
2 - 1 
#include	"u.h"
2 
#include	"lib.h"
3 
#include	"dat.h"
4 
#include	"fns.h"
5 
#include	"error.h"
6 
 
7 
int chandebug=0;		/* toggled by sysr1 */
8 
QLock chanprint;		/* probably asking for trouble (deadlocks) -rsc */
9 
 
10 
int domount(Chan**, Mhead**);
11 
 
12 
void
13 
dumpmount(void)		/* DEBUGGING */
14 
{
15 
	Pgrp *pg;
16 
	Mount *t;
17 
	Mhead **h, **he, *f;
18 
 
19 
	if(up == nil){
20 
		print("no process for dumpmount\n");
21 
		return;
22 
	}
23 
	pg = up->pgrp;
24 
	if(pg == nil){
25 
		print("no pgrp for dumpmount\n");
26 
		return;
27 
	}
28 
	rlock(&pg->ns);
29 
	if(waserror()) {
30 
		runlock(&pg->ns);
31 
		nexterror();
32 
	}
33 
 
34 
	he = &pg->mnthash[MNTHASH];
35 
	for(h = pg->mnthash; h < he; h++) {
36 
		for(f = *h; f; f = f->hash) {
37 
			print("head: %p: %s 0x%llux.%lud %C %lud -> \n", f,
38 
				f->from->name->s, f->from->qid.path,
39 
				f->from->qid.vers, devtab[f->from->type]->dc,
40 
				f->from->dev);
41 
			for(t = f->mount; t; t = t->next)
42 
				print("\t%p: %s (umh %p) (path %.8llux dev %C %lud)\n", t, t->to->name->s, t->to->umh, t->to->qid.path, devtab[t->to->type]->dc, t->to->dev);
43 
		}
44 
	}
45 
	poperror();
46 
	runlock(&pg->ns);
47 
}
48 
 
49 
 
50 
char*
51 
c2name(Chan *c)		/* DEBUGGING */
52 
{
53 
	if(c == nil)
54 
		return "<nil chan>";
55 
	if(c->name == nil)
56 
		return "<nil name>";
57 
	if(c->name->s == nil)
58 
		return "<nil name.s>";
59 
	return c->name->s;
60 
}
61 
 
62 
enum
63 
{
64 
	CNAMESLOP	= 20
65 
};
66 
 
67 
struct
68 
{
69 
	Lock lk;
70 
	int	fid;
71 
	Chan	*free;
72 
	Chan	*list;
73 
}chanalloc;
74 
 
75 
typedef struct Elemlist Elemlist;
76 
 
77 
struct Elemlist
78 
{
79 
	char	*name;	/* copy of name, so '/' can be overwritten */
80 
	int	nelems;
81 
	char	**elems;
82 
	int	*off;
83 
	int	mustbedir;
84 
};
85 
 
86 
#define SEP(c) ((c) == 0 || (c) == '/')
87 
void cleancname(Cname*);
88 
 
89 
int
90 
isdotdot(char *p)
91 
{
92 
	return p[0]=='.' && p[1]=='.' && p[2]=='\0';
93 
}
94 
 
95 
int
96 
incref(Ref *r)
97 
{
98 
	int x;
99 
 
100 
	lock(&r->lk);
101 
	x = ++r->ref;
102 
	unlock(&r->lk);
103 
	return x;
104 
}
105 
 
106 
int
107 
decref(Ref *r)
108 
{
109 
	int x;
110 
 
111 
	lock(&r->lk);
112 
	x = --r->ref;
113 
	unlock(&r->lk);
114 
	if(x < 0)
115 
		panic("decref, pc=0x%p", getcallerpc(&r));
116 
 
117 
	return x;
118 
}
119 
 
120 
/*
121 
 * Rather than strncpy, which zeros the rest of the buffer, kstrcpy
122 
 * truncates if necessary, always zero terminates, does not zero fill,
123 
 * and puts ... at the end of the string if it's too long.  Usually used to
124 
 * save a string in up->genbuf;
125 
 */
126 
void
127 
kstrcpy(char *s, char *t, int ns)
128 
{
129 
	int nt;
130 
 
131 
	nt = strlen(t);
132 
	if(nt+1 <= ns){
133 
		memmove(s, t, nt+1);
134 
		return;
135 
	}
136 
	/* too long */
137 
	if(ns < 4){
138 
		/* but very short! */
139 
		strncpy(s, t, ns);
140 
		return;
141 
	}
142 
	/* truncate with ... at character boundary (very rare case) */
143 
	memmove(s, t, ns-4);
144 
	ns -= 4;
145 
	s[ns] = '\0';
146 
	/* look for first byte of UTF-8 sequence by skipping continuation bytes */
147 
	while(ns>0 && (s[--ns]&0xC0)==0x80)
148 
		;
149 
	strcpy(s+ns, "...");
150 
}
151 
 
152 
int
153 
emptystr(char *s)
154 
{
155 
	if(s == nil)
156 
		return 1;
157 
	if(s[0] == '\0')
158 
		return 1;
159 
	return 0;
160 
}
161 
 
162 
/*
163 
 * Atomically replace *p with copy of s
164 
 */
165 
void
166 
kstrdup(char **p, char *s)
167 
{
168 
	int n;
169 
	char *t, *prev;
170 
 
171 
	n = strlen(s)+1;
172 
	/* if it's a user, we can wait for memory; if not, something's very wrong */
173 
	if(up){
174 
		t = smalloc(n);
175 
		setmalloctag(t, getcallerpc(&p));
176 
	}else{
177 
		t = malloc(n);
178 
		if(t == nil)
179 
			panic("kstrdup: no memory");
180 
	}
181 
	memmove(t, s, n);
182 
	prev = *p;
183 
	*p = t;
184 
	free(prev);
185 
}
186 
 
187 
void
188 
chandevreset(void)
189 
{
190 
	int i;
191 
 
192 
	for(i=0; devtab[i] != nil; i++)
193 
		devtab[i]->reset();
194 
}
195 
 
196 
void
197 
chandevinit(void)
198 
{
199 
	int i;
200 
 
201 
	for(i=0; devtab[i] != nil; i++)
202 
		devtab[i]->init();
203 
}
204 
 
205 
void
206 
chandevshutdown(void)
207 
{
208 
	int i;
209 
 
210 
	/* shutdown in reverse order */
211 
	for(i=0; devtab[i] != nil; i++)
212 
		;
213 
	for(i--; i >= 0; i--)
214 
		devtab[i]->shutdown();
215 
}
216 
 
217 
Chan*
218 
newchan(void)
219 
{
220 
	Chan *c;
221 
 
222 
	lock(&chanalloc.lk);
223 
	c = chanalloc.free;
224 
	if(c != 0)
225 
		chanalloc.free = c->next;
226 
	unlock(&chanalloc.lk);
227 
 
228 
	if(c == nil) {
229 
		c = smalloc(sizeof(Chan));
230 
		lock(&chanalloc.lk);
231 
		c->fid = ++chanalloc.fid;
232 
		c->link = chanalloc.list;
233 
		chanalloc.list = c;
234 
		unlock(&chanalloc.lk);
235 
	}
236 
 
237 
	/* if you get an error before associating with a dev,
238 
	   close calls rootclose, a nop */
239 
	c->type = 0;
240 
	c->flag = 0;
241 
	c->ref.ref = 1;
242 
	c->dev = 0;
243 
	c->offset = 0;
244 
	c->iounit = 0;
245 
	c->umh = 0;
246 
	c->uri = 0;
247 
	c->dri = 0;
248 
	c->aux = 0;
249 
	c->mchan = 0;
250 
	c->mcp = 0;
251 
	c->mux = 0;
252 
	memset(&c->mqid, 0, sizeof(c->mqid));
253 
	c->name = 0;
254 
	return c;
255 
}
256 
 
257 
static Ref ncname;
258 
 
259 
Cname*
260 
newcname(char *s)
261 
{
262 
	Cname *n;
263 
	int i;
264 
 
265 
	n = smalloc(sizeof(Cname));
266 
	i = strlen(s);
267 
	n->len = i;
268 
	n->alen = i+CNAMESLOP;
269 
	n->s = smalloc(n->alen);
270 
	memmove(n->s, s, i+1);
271 
	n->ref.ref = 1;
272 
	incref(&ncname);
273 
	return n;
274 
}
275 
 
276 
void
277 
cnameclose(Cname *n)
278 
{
279 
	if(n == nil)
280 
		return;
281 
	if(decref(&n->ref))
282 
		return;
283 
	decref(&ncname);
284 
	free(n->s);
285 
	free(n);
286 
}
287 
 
288 
Cname*
289 
addelem(Cname *n, char *s)
290 
{
291 
	int i, a;
292 
	char *t;
293 
	Cname *new;
294 
 
295 
	if(s[0]=='.' && s[1]=='\0')
296 
		return n;
297 
 
298 
	if(n->ref.ref > 1){
299 
		/* copy on write */
300 
		new = newcname(n->s);
301 
		cnameclose(n);
302 
		n = new;
303 
	}
304 
 
305 
	i = strlen(s);
306 
	if(n->len+1+i+1 > n->alen){
307 
		a = n->len+1+i+1 + CNAMESLOP;
308 
		t = smalloc(a);
309 
		memmove(t, n->s, n->len+1);
310 
		free(n->s);
311 
		n->s = t;
312 
		n->alen = a;
313 
	}
314 
	if(n->len>0 && n->s[n->len-1]!='/' && s[0]!='/')	/* don't insert extra slash if one is present */
315 
		n->s[n->len++] = '/';
316 
	memmove(n->s+n->len, s, i+1);
317 
	n->len += i;
318 
	if(isdotdot(s))
319 
		cleancname(n);
320 
	return n;
321 
}
322 
 
323 
void
324 
chanfree(Chan *c)
325 
{
326 
	c->flag = CFREE;
327 
 
328 
	if(c->umh != nil){
329 
		putmhead(c->umh);
330 
		c->umh = nil;
331 
	}
332 
	if(c->umc != nil){
333 
		cclose(c->umc);
334 
		c->umc = nil;
335 
	}
336 
	if(c->mux != nil){
337 
		muxclose(c->mux);
338 
		c->mux = nil;
339 
	}
340 
	if(c->mchan != nil){
341 
		cclose(c->mchan);
342 
		c->mchan = nil;
343 
	}
344 
 
345 
	cnameclose(c->name);
346 
 
347 
	lock(&chanalloc.lk);
348 
	c->next = chanalloc.free;
349 
	chanalloc.free = c;
350 
	unlock(&chanalloc.lk);
351 
}
352 
 
353 
void
354 
cclose(Chan *c)
355 
{
356 
	if(c->flag&CFREE)
357 
		panic("cclose %p", getcallerpc(&c));
358 
 
359 
	if(decref(&c->ref))
360 
		return;
361 
 
362 
	if(!waserror()){
363 
		devtab[c->type]->close(c);
364 
		poperror();
365 
	}
366 
	chanfree(c);
367 
}
368 
 
369 
/*
370 
 * Make sure we have the only copy of c.  (Copy on write.)
371 
 */
372 
Chan*
373 
cunique(Chan *c)
374 
{
375 
	Chan *nc;
376 
 
377 
	if(c->ref.ref != 1) {
378 
		nc = cclone(c);
379 
		cclose(c);
380 
		c = nc;
381 
	}
382 
 
383 
	return c;
384 
}
385 
 
386 
int
387 
eqqid(Qid a, Qid b)
388 
{
389 
	return a.path==b.path && a.vers==b.vers;
390 
}
391 
 
392 
int
393 
eqchan(Chan *a, Chan *b, int pathonly)
394 
{
395 
	if(a->qid.path != b->qid.path)
396 
		return 0;
397 
	if(!pathonly && a->qid.vers!=b->qid.vers)
398 
		return 0;
399 
	if(a->type != b->type)
400 
		return 0;
401 
	if(a->dev != b->dev)
402 
		return 0;
403 
	return 1;
404 
}
405 
 
406 
int
407 
eqchantdqid(Chan *a, int type, int dev, Qid qid, int pathonly)
408 
{
409 
	if(a->qid.path != qid.path)
410 
		return 0;
411 
	if(!pathonly && a->qid.vers!=qid.vers)
412 
		return 0;
413 
	if(a->type != type)
414 
		return 0;
415 
	if(a->dev != dev)
416 
		return 0;
417 
	return 1;
418 
}
419 
 
420 
Mhead*
421 
newmhead(Chan *from)
422 
{
423 
	Mhead *mh;
424 
 
425 
	mh = smalloc(sizeof(Mhead));
426 
	mh->ref.ref = 1;
427 
	mh->from = from;
428 
	incref(&from->ref);
429 
 
430 
/*
431 
	n = from->name->len;
432 
	if(n >= sizeof(mh->fromname))
433 
		n = sizeof(mh->fromname)-1;
434 
	memmove(mh->fromname, from->name->s, n);
435 
	mh->fromname[n] = 0;
436 
*/
437 
	return mh;
438 
}
439 
 
440 
int
441 
cmount(Chan **newp, Chan *old, int flag, char *spec)
442 
{
443 
	Pgrp *pg;
444 
	int order, flg;
445 
	Mhead *m, **l, *mh;
446 
	Mount *nm, *f, *um, **h;
447 
	Chan *new;
448 
 
449 
	if(QTDIR & (old->qid.type^(*newp)->qid.type))
450 
		error(Emount);
451 
 
452 
if(old->umh)print("cmount old extra umh\n");
453 
 
454 
	order = flag&MORDER;
455 
 
456 
	if((old->qid.type&QTDIR)==0 && order != MREPL)
457 
		error(Emount);
458 
 
459 
	new = *newp;
460 
	mh = new->umh;
461 
 
462 
	/*
463 
	 * Not allowed to bind when the old directory
464 
	 * is itself a union.  (Maybe it should be allowed, but I don't see
465 
	 * what the semantics would be.)
466 
	 *
467 
	 * We need to check mh->mount->next to tell unions apart from
468 
	 * simple mount points, so that things like
469 
	 *	mount -c fd /root
470 
	 *	bind -c /root /
471 
	 * work.  The check of mount->mflag catches things like
472 
	 *	mount fd /root
473 
	 *	bind -c /root /
474 
	 *
475 
	 * This is far more complicated than it should be, but I don't
476 
	 * see an easier way at the moment.		-rsc
477 
	 */
478 
	if((flag&MCREATE) && mh && mh->mount
479 
	&& (mh->mount->next || !(mh->mount->mflag&MCREATE)))
480 
		error(Emount);
481 
 
482 
	pg = up->pgrp;
483 
	wlock(&pg->ns);
484 
 
485 
	l = &MOUNTH(pg, old->qid);
486 
	for(m = *l; m; m = m->hash) {
487 
		if(eqchan(m->from, old, 1))
488 
			break;
489 
		l = &m->hash;
490 
	}
491 
 
492 
	if(m == nil) {
493 
		/*
494 
		 *  nothing mounted here yet.  create a mount
495 
		 *  head and add to the hash table.
496 
		 */
497 
		m = newmhead(old);
498 
		*l = m;
499 
 
500 
		/*
501 
		 *  if this is a union mount, add the old
502 
		 *  node to the mount chain.
503 
		 */
504 
		if(order != MREPL)
505 
			m->mount = newmount(m, old, 0, 0);
506 
	}
507 
	wlock(&m->lock);
508 
	if(waserror()){
509 
		wunlock(&m->lock);
510 
		nexterror();
511 
	}
512 
	wunlock(&pg->ns);
513 
 
514 
	nm = newmount(m, new, flag, spec);
515 
	if(mh != nil && mh->mount != nil) {
516 
		/*
517 
		 *  copy a union when binding it onto a directory
518 
		 */
519 
		flg = order;
520 
		if(order == MREPL)
521 
			flg = MAFTER;
522 
		h = &nm->next;
523 
		um = mh->mount;
524 
		for(um = um->next; um; um = um->next) {
525 
			f = newmount(m, um->to, flg, um->spec);
526 
			*h = f;
527 
			h = &f->next;
528 
		}
529 
	}
530 
 
531 
	if(m->mount && order == MREPL) {
532 
		mountfree(m->mount);
533 
		m->mount = 0;
534 
	}
535 
 
536 
	if(flag & MCREATE)
537 
		nm->mflag |= MCREATE;
538 
 
539 
	if(m->mount && order == MAFTER) {
540 
		for(f = m->mount; f->next; f = f->next)
541 
			;
542 
		f->next = nm;
543 
	}
544 
	else {
545 
		for(f = nm; f->next; f = f->next)
546 
			;
547 
		f->next = m->mount;
548 
		m->mount = nm;
549 
	}
550 
 
551 
	wunlock(&m->lock);
552 
	poperror();
553 
	return nm->mountid;
554 
}
555 
 
556 
void
557 
cunmount(Chan *mnt, Chan *mounted)
558 
{
559 
	Pgrp *pg;
560 
	Mhead *m, **l;
561 
	Mount *f, **p;
562 
 
563 
	if(mnt->umh)	/* should not happen */
564 
		print("cunmount newp extra umh %p has %p\n", mnt, mnt->umh);
565 
 
566 
	/*
567 
	 * It _can_ happen that mounted->umh is non-nil,
568 
	 * because mounted is the result of namec(Aopen)
569 
	 * (see sysfile.c:/^sysunmount).
570 
	 * If we open a union directory, it will have a umh.
571 
	 * Although surprising, this is okay, since the
572 
	 * cclose will take care of freeing the umh.
573 
	 */
574 
 
575 
	pg = up->pgrp;
576 
	wlock(&pg->ns);
577 
 
578 
	l = &MOUNTH(pg, mnt->qid);
579 
	for(m = *l; m; m = m->hash) {
580 
		if(eqchan(m->from, mnt, 1))
581 
			break;
582 
		l = &m->hash;
583 
	}
584 
 
585 
	if(m == 0) {
586 
		wunlock(&pg->ns);
587 
		error(Eunmount);
588 
	}
589 
 
590 
	wlock(&m->lock);
591 
	if(mounted == 0) {
592 
		*l = m->hash;
593 
		wunlock(&pg->ns);
594 
		mountfree(m->mount);
595 
		m->mount = nil;
596 
		cclose(m->from);
597 
		wunlock(&m->lock);
598 
		putmhead(m);
599 
		return;
600 
	}
601 
 
602 
	p = &m->mount;
603 
	for(f = *p; f; f = f->next) {
604 
		/* BUG: Needs to be 2 pass */
605 
		if(eqchan(f->to, mounted, 1) ||
606 
		  (f->to->mchan && eqchan(f->to->mchan, mounted, 1))) {
607 
			*p = f->next;
608 
			f->next = 0;
609 
			mountfree(f);
610 
			if(m->mount == nil) {
611 
				*l = m->hash;
612 
				cclose(m->from);
613 
				wunlock(&m->lock);
614 
				wunlock(&pg->ns);
615 
				putmhead(m);
616 
				return;
617 
			}
618 
			wunlock(&m->lock);
619 
			wunlock(&pg->ns);
620 
			return;
621 
		}
622 
		p = &f->next;
623 
	}
624 
	wunlock(&m->lock);
625 
	wunlock(&pg->ns);
626 
	error(Eunion);
627 
}
628 
 
629 
Chan*
630 
cclone(Chan *c)
631 
{
632 
	Chan *nc;
633 
	Walkqid *wq;
634 
 
635 
	wq = devtab[c->type]->walk(c, nil, nil, 0);
636 
	if(wq == nil)
637 
		error("clone failed");
638 
	nc = wq->clone;
639 
	free(wq);
640 
	nc->name = c->name;
641 
	if(c->name)
642 
		incref(&c->name->ref);
643 
	return nc;
644 
}
645 
 
646 
int
647 
findmount(Chan **cp, Mhead **mp, int type, int dev, Qid qid)
648 
{
649 
	Pgrp *pg;
650 
	Mhead *m;
651 
 
652 
	pg = up->pgrp;
653 
	rlock(&pg->ns);
654 
	for(m = MOUNTH(pg, qid); m; m = m->hash){
655 
		rlock(&m->lock);
656 
if(m->from == nil){
657 
	print("m %p m->from 0\n", m);
658 
	runlock(&m->lock);
659 
	continue;
660 
}
661 
		if(eqchantdqid(m->from, type, dev, qid, 1)) {
662 
			runlock(&pg->ns);
663 
			if(mp != nil){
664 
				incref(&m->ref);
665 
				if(*mp != nil)
666 
					putmhead(*mp);
667 
				*mp = m;
668 
			}
669 
			if(*cp != nil)
670 
				cclose(*cp);
671 
			incref(&m->mount->to->ref);
672 
			*cp = m->mount->to;
673 
			runlock(&m->lock);
674 
			return 1;
675 
		}
676 
		runlock(&m->lock);
677 
	}
678 
 
679 
	runlock(&pg->ns);
680 
	return 0;
681 
}
682 
 
683 
int
684 
domount(Chan **cp, Mhead **mp)
685 
{
686 
	return findmount(cp, mp, (*cp)->type, (*cp)->dev, (*cp)->qid);
687 
}
688 
 
689 
Chan*
690 
undomount(Chan *c, Cname *name)
691 
{
692 
	Chan *nc;
693 
	Pgrp *pg;
694 
	Mount *t;
695 
	Mhead **h, **he, *f;
696 
 
697 
	pg = up->pgrp;
698 
	rlock(&pg->ns);
699 
	if(waserror()) {
700 
		runlock(&pg->ns);
701 
		nexterror();
702 
	}
703 
 
704 
	he = &pg->mnthash[MNTHASH];
705 
	for(h = pg->mnthash; h < he; h++) {
706 
		for(f = *h; f; f = f->hash) {
707 
			if(strcmp(f->from->name->s, name->s) != 0)
708 
				continue;
709 
			for(t = f->mount; t; t = t->next) {
710 
				if(eqchan(c, t->to, 1)) {
711 
					/*
712 
					 * We want to come out on the left hand side of the mount
713 
					 * point using the element of the union that we entered on.
714 
					 * To do this, find the element that has a from name of
715 
					 * c->name->s.
716 
					 */
717 
					if(strcmp(t->head->from->name->s, name->s) != 0)
718 
						continue;
719 
					nc = t->head->from;
720 
					incref(&nc->ref);
721 
					cclose(c);
722 
					c = nc;
723 
					break;
724 
				}
725 
			}
726 
		}
727 
	}
728 
	poperror();
729 
	runlock(&pg->ns);
730 
	return c;
731 
}
732 
 
733 
/*
734 
 * Either walks all the way or not at all.  No partial results in *cp.
735 
 * *nerror is the number of names to display in an error message.
736 
 */
737 
static char Edoesnotexist[] = "does not exist";
738 
int
739 
walk(Chan **cp, char **names, int nnames, int nomount, int *nerror)
740 
{
741 
	int dev, dotdot, i, n, nhave, ntry, type;
742 
	Chan *c, *nc;
743 
	Cname *cname;
744 
	Mount *f;
745 
	Mhead *mh, *nmh;
746 
	Walkqid *wq;
747 
 
748 
	c = *cp;
749 
	incref(&c->ref);
750 
	cname = c->name;
751 
	incref(&cname->ref);
752 
	mh = nil;
753 
 
754 
	/*
755 
	 * While we haven't gotten all the way down the path:
756 
	 *    1. step through a mount point, if any
757 
	 *    2. send a walk request for initial dotdot or initial prefix without dotdot
758 
	 *    3. move to the first mountpoint along the way.
759 
	 *    4. repeat.
760 
	 *
761 
	 * An invariant is that each time through the loop, c is on the undomount
762 
	 * side of the mount point, and c's name is cname.
763 
	 */
764 
	for(nhave=0; nhave<nnames; nhave+=n){
765 
		if((c->qid.type&QTDIR)==0){
766 
			if(nerror)
767 
				*nerror = nhave;
768 
			cnameclose(cname);
769 
			cclose(c);
770 
			strcpy(up->errstr, Enotdir);
771 
			if(mh != nil)
772 
{print("walk 1\n");
773 
				putmhead(mh);
774 
}
775 
			return -1;
776 
		}
777 
		ntry = nnames - nhave;
778 
		if(ntry > MAXWELEM)
779 
			ntry = MAXWELEM;
780 
		dotdot = 0;
781 
		for(i=0; i<ntry; i++){
782 
			if(isdotdot(names[nhave+i])){
783 
				if(i==0) {
784 
					dotdot = 1;
785 
					ntry = 1;
786 
				} else
787 
					ntry = i;
788 
				break;
789 
			}
790 
		}
791 
 
792 
		if(!dotdot && !nomount)
793 
			domount(&c, &mh);
794 
 
795 
		type = c->type;
796 
		dev = c->dev;
797 
 
798 
		if((wq = devtab[type]->walk(c, nil, names+nhave, ntry)) == nil){
799 
			/* try a union mount, if any */
800 
			if(mh && !nomount){
801 
				/*
802 
				 * mh->mount == c, so start at mh->mount->next
803 
				 */
804 
				rlock(&mh->lock);
805 
				for(f = mh->mount->next; f; f = f->next)
806 
					if((wq = devtab[f->to->type]->walk(f->to, nil, names+nhave, ntry)) != nil)
807 
						break;
808 
				runlock(&mh->lock);
809 
				if(f != nil){
810 
					type = f->to->type;
811 
					dev = f->to->dev;
812 
				}
813 
			}
814 
			if(wq == nil){
815 
				cclose(c);
816 
				cnameclose(cname);
817 
				if(nerror)
818 
					*nerror = nhave+1;
819 
				if(mh != nil)
820 
					putmhead(mh);
821 
				return -1;
822 
			}
823 
		}
824 
 
825 
		nmh = nil;
826 
		if(dotdot) {
827 
			assert(wq->nqid == 1);
828 
			assert(wq->clone != nil);
829 
 
830 
			cname = addelem(cname, "..");
831 
			nc = undomount(wq->clone, cname);
832 
			n = 1;
833 
		} else {
834 
			nc = nil;
835 
			if(!nomount)
836 
				for(i=0; i<wq->nqid && i<ntry-1; i++)
837 
					if(findmount(&nc, &nmh, type, dev, wq->qid[i]))
838 
						break;
839 
			if(nc == nil){	/* no mount points along path */
840 
				if(wq->clone == nil){
841 
					cclose(c);
842 
					cnameclose(cname);
843 
					if(wq->nqid==0 || (wq->qid[wq->nqid-1].type&QTDIR)){
844 
						if(nerror)
845 
							*nerror = nhave+wq->nqid+1;
846 
						strcpy(up->errstr, Edoesnotexist);
847 
					}else{
848 
						if(nerror)
849 
							*nerror = nhave+wq->nqid;
850 
						strcpy(up->errstr, Enotdir);
851 
					}
852 
					free(wq);
853 
					if(mh != nil)
854 
						putmhead(mh);
855 
					return -1;
856 
				}
857 
				n = wq->nqid;
858 
				nc = wq->clone;
859 
			}else{		/* stopped early, at a mount point */
860 
				if(wq->clone != nil){
861 
					cclose(wq->clone);
862 
					wq->clone = nil;
863 
				}
864 
				n = i+1;
865 
			}
866 
			for(i=0; i<n; i++)
867 
				cname = addelem(cname, names[nhave+i]);
868 
		}
869 
		cclose(c);
870 
		c = nc;
871 
		putmhead(mh);
872 
		mh = nmh;
873 
		free(wq);
874 
	}
875 
 
876 
	putmhead(mh);
877 
 
878 
	c = cunique(c);
879 
 
880 
	if(c->umh != nil){	//BUG
881 
		print("walk umh\n");
882 
		putmhead(c->umh);
883 
		c->umh = nil;
884 
	}
885 
 
886 
	cnameclose(c->name);
887 
	c->name = cname;
888 
 
889 
	cclose(*cp);
890 
	*cp = c;
891 
	if(nerror)
892 
		*nerror = 0;
893 
	return 0;
894 
}
895 
 
896 
/*
897 
 * c is a mounted non-creatable directory.  find a creatable one.
898 
 */
899 
Chan*
900 
createdir(Chan *c, Mhead *m)
901 
{
902 
	Chan *nc;
903 
	Mount *f;
904 
 
905 
	rlock(&m->lock);
906 
	if(waserror()) {
907 
		runlock(&m->lock);
908 
		nexterror();
909 
	}
910 
	for(f = m->mount; f; f = f->next) {
911 
		if(f->mflag&MCREATE) {
912 
			nc = cclone(f->to);
913 
			runlock(&m->lock);
914 
			poperror();
915 
			cclose(c);
916 
			return nc;
917 
		}
918 
	}
919 
	error(Enocreate);
920 
	return 0;
921 
}
922 
 
923 
void
924 
saveregisters(void)
925 
{
926 
}
927 
 
928 
/*
929 
 * In place, rewrite name to compress multiple /, eliminate ., and process ..
930 
 */
931 
void
932 
cleancname(Cname *n)
933 
{
934 
	char *p;
935 
 
936 
	if(n->s[0] == '#'){
937 
		p = strchr(n->s, '/');
938 
		if(p == nil)
939 
			return;
940 
		cleanname(p);
941 
 
942 
		/*
943 
		 * The correct name is #i rather than #i/,
944 
		 * but the correct name of #/ is #/.
945 
		 */
946 
		if(strcmp(p, "/")==0 && n->s[1] != '/')
947 
			*p = '\0';
948 
	}else
949 
		cleanname(n->s);
950 
	n->len = strlen(n->s);
951 
}
952 
 
953 
static void
954 
growparse(Elemlist *e)
955 
{
956 
	char **new;
957 
	int *inew;
958 
	enum { Delta = 8 };
959 
 
960 
	if(e->nelems % Delta == 0){
961 
		new = smalloc((e->nelems+Delta) * sizeof(char*));
962 
		memmove(new, e->elems, e->nelems*sizeof(char*));
963 
		free(e->elems);
964 
		e->elems = new;
965 
		inew = smalloc((e->nelems+Delta+1) * sizeof(int));
966 
		memmove(inew, e->off, e->nelems*sizeof(int));
967 
		free(e->off);
968 
		e->off = inew;
969 
	}
970 
}
971 
 
972 
/*
973 
 * The name is known to be valid.
974 
 * Copy the name so slashes can be overwritten.
975 
 * An empty string will set nelem=0.
976 
 * A path ending in / or /. or /.//./ etc. will have
977 
 * e.mustbedir = 1, so that we correctly
978 
 * reject, e.g., "/adm/users/." when /adm/users is a file
979 
 * rather than a directory.
980 
 */
981 
static void
982 
parsename(char *name, Elemlist *e)
983 
{
984 
	char *slash;
985 
 
986 
	kstrdup(&e->name, name);
987 
	name = e->name;
988 
	e->nelems = 0;
989 
	e->elems = nil;
990 
	e->off = smalloc(sizeof(int));
991 
	e->off[0] = skipslash(name) - name;
992 
	for(;;){
993 
		name = skipslash(name);
994 
		if(*name=='\0'){
995 
			e->mustbedir = 1;
996 
			break;
997 
		}
998 
		growparse(e);
999 
		e->elems[e->nelems++] = name;
1000 
		slash = utfrune(name, '/');
1001 
		if(slash == nil){
1002 
			e->off[e->nelems] = name+strlen(name) - e->name;
1003 
			e->mustbedir = 0;
1004 
			break;
1005 
		}
1006 
		e->off[e->nelems] = slash - e->name;
1007 
		*slash++ = '\0';
1008 
		name = slash;
1009 
	}
1010 
}
1011 
 
1012 
void*
1013 
mymemrchr(void *va, int c, long n)
1014 
{
1015 
	uchar *a, *e;
1016 
 
1017 
	a = va;
1018 
	for(e=a+n-1; e>a; e--)
1019 
		if(*e == c)
1020 
			return e;
1021 
	return nil;
1022 
}
1023 
 
1024 
/*
1025 
 * Turn a name into a channel.
1026 
 * &name[0] is known to be a valid address.  It may be a kernel address.
1027 
 *
1028 
 * Opening with amode Aopen, Acreate, or Aremove guarantees
1029 
 * that the result will be the only reference to that particular fid.
1030 
 * This is necessary since we might pass the result to
1031 
 * devtab[]->remove().
1032 
 *
1033 
 * Opening Atodir, Amount, or Aaccess does not guarantee this.
1034 
 *
1035 
 * Opening Aaccess can, under certain conditions, return a
1036 
 * correct Chan* but with an incorrect Cname attached.
1037 
 * Since the functions that open Aaccess (sysstat, syswstat, sys_stat)
1038 
 * do not use the Cname*, this avoids an unnecessary clone.
1039 
 */
1040 
Chan*
1041 
namec(char *aname, int amode, int omode, ulong perm)
1042 
{
1043 
	int n, prefix, len, t, nomount, npath;
1044 
	Chan *c, *cnew;
1045 
	Cname *cname;
1046 
	Elemlist e;
1047 
	Rune r;
1048 
	Mhead *m;
1049 
	char *createerr, tmperrbuf[ERRMAX];
1050 
	char *name;
1051 
 
1052 
	name = aname;
1053 
	if(name[0] == '\0')
1054 
		error("empty file name");
1055 
	validname(name, 1);
1056 
 
1057 
	/*
1058 
	 * Find the starting off point (the current slash, the root of
1059 
	 * a device tree, or the current dot) as well as the name to
1060 
	 * evaluate starting there.
1061 
	 */
1062 
	nomount = 0;
1063 
	switch(name[0]){
1064 
	case '/':
1065 
		c = up->slash;
1066 
		incref(&c->ref);
1067 
		break;
1068 
 
1069 
	case '#':
1070 
		nomount = 1;
1071 
		up->genbuf[0] = '\0';
1072 
		n = 0;
1073 
		while(*name!='\0' && (*name != '/' || n < 2)){
1074 
			if(n >= sizeof(up->genbuf)-1)
1075 
				error(Efilename);
1076 
			up->genbuf[n++] = *name++;
1077 
		}
1078 
		up->genbuf[n] = '\0';
1079 
		/*
1080 
		 *  noattach is sandboxing.
1081 
		 *
1082 
		 *  the OK exceptions are:
1083 
		 *	|  it only gives access to pipes you create
1084 
		 *	d  this process's file descriptors
1085 
		 *	e  this process's environment
1086 
		 *  the iffy exceptions are:
1087 
		 *	c  time and pid, but also cons and consctl
1088 
		 *	p  control of your own processes (and unfortunately
1089 
		 *	   any others left unprotected)
1090 
		 */
1091 
		n = chartorune(&r, up->genbuf+1)+1;
1092 
		/* actually / is caught by parsing earlier */
1093 
		if(utfrune("M", r))
1094 
			error(Enoattach);
1095 
		if(up->pgrp->noattach && utfrune("|decp", r)==nil)
1096 
			error(Enoattach);
1097 
		t = devno(r, 1);
1098 
		if(t == -1)
1099 
			error(Ebadsharp);
1100 
		c = devtab[t]->attach(up->genbuf+n);
1101 
		break;
1102 
 
1103 
	default:
1104 
		c = up->dot;
1105 
		incref(&c->ref);
1106 
		break;
1107 
	}
1108 
	prefix = name - aname;
1109 
 
1110 
	e.name = nil;
1111 
	e.elems = nil;
1112 
	e.off = nil;
1113 
	e.nelems = 0;
1114 
	if(waserror()){
1115 
		cclose(c);
1116 
		free(e.name);
1117 
		free(e.elems);
1118 
		free(e.off);
1119 
//dumpmount();
1120 
		nexterror();
1121 
	}
1122 
 
1123 
	/*
1124 
	 * Build a list of elements in the path.
1125 
	 */
1126 
	parsename(name, &e);
1127 
 
1128 
	/*
1129 
	 * On create, ....
1130 
	 */
1131 
	if(amode == Acreate){
1132 
		/* perm must have DMDIR if last element is / or /. */
1133 
		if(e.mustbedir && !(perm&DMDIR)){
1134 
			npath = e.nelems;
1135 
			strcpy(tmperrbuf, "create without DMDIR");
1136 
			goto NameError;
1137 
		}
1138 
 
1139 
		/* don't try to walk the last path element just yet. */
1140 
		if(e.nelems == 0)
1141 
			error(Eexist);
1142 
		e.nelems--;
1143 
	}
1144 
 
1145 
	if(walk(&c, e.elems, e.nelems, nomount, &npath) < 0){
1146 
		if(npath < 0 || npath > e.nelems){
1147 
			print("namec %s walk error npath=%d\n", aname, npath);
1148 
			nexterror();
1149 
		}
1150 
		strcpy(tmperrbuf, up->errstr);
1151 
	NameError:
1152 
		len = prefix+e.off[npath];
1153 
		if(len < ERRMAX/3 || (name=mymemrchr(aname, '/', len))==nil || name==aname)
1154 
			snprint(up->genbuf, sizeof up->genbuf, "%.*s", len, aname);
1155 
		else
1156 
			snprint(up->genbuf, sizeof up->genbuf, "...%.*s", (int)(len-(name-aname)), name);
1157 
		snprint(up->errstr, ERRMAX, "%#q %s", up->genbuf, tmperrbuf);
1158 
		nexterror();
1159 
	}
1160 
 
1161 
	if(e.mustbedir && !(c->qid.type&QTDIR)){
1162 
		npath = e.nelems;
1163 
		strcpy(tmperrbuf, "not a directory");
1164 
		goto NameError;
1165 
	}
1166 
 
1167 
	if(amode == Aopen && (omode&3) == OEXEC && (c->qid.type&QTDIR)){
1168 
		npath = e.nelems;
1169 
		error("cannot exec directory");
1170 
	}
1171 
 
1172 
	switch(amode){
1173 
	case Aaccess:
1174 
		if(!nomount)
1175 
			domount(&c, nil);
1176 
		break;
1177 
 
1178 
	case Abind:
1179 
		m = nil;
1180 
		if(!nomount)
1181 
			domount(&c, &m);
1182 
		if(c->umh != nil)
1183 
			putmhead(c->umh);
1184 
		c->umh = m;
1185 
		break;
1186 
 
1187 
	case Aremove:
1188 
	case Aopen:
1189 
	Open:
1190 
		/* save the name; domount might change c */
1191 
		cname = c->name;
1192 
		incref(&cname->ref);
1193 
		m = nil;
1194 
		if(!nomount)
1195 
			domount(&c, &m);
1196 
 
1197 
		/* our own copy to open or remove */
1198 
		c = cunique(c);
1199 
 
1200 
		/* now it's our copy anyway, we can put the name back */
1201 
		cnameclose(c->name);
1202 
		c->name = cname;
1203 
 
1204 
		switch(amode){
1205 
		case Aremove:
1206 
			putmhead(m);
1207 
			break;
1208 
 
1209 
		case Aopen:
1210 
		case Acreate:
1211 
if(c->umh != nil){
1212 
	print("cunique umh Open\n");
1213 
	putmhead(c->umh);
1214 
	c->umh = nil;
1215 
}
1216 
 
1217 
			/* only save the mount head if it's a multiple element union */
1218 
			if(m && m->mount && m->mount->next)
1219 
				c->umh = m;
1220 
			else
1221 
				putmhead(m);
1222 
 
1223 
			/* save registers else error() in open has wrong value of c saved */
1224 
			saveregisters();
1225 
 
1226 
			if(omode == OEXEC)
1227 
				c->flag &= ~CCACHE;
1228 
 
1229 
			c = devtab[c->type]->open(c, omode&~OCEXEC);
1230 
 
1231 
			if(omode & OCEXEC)
1232 
				c->flag |= CCEXEC;
1233 
			if(omode & ORCLOSE)
1234 
				c->flag |= CRCLOSE;
1235 
			break;
1236 
		}
1237 
		break;
1238 
 
1239 
	case Atodir:
1240 
		/*
1241 
		 * Directories (e.g. for cd) are left before the mount point,
1242 
		 * so one may mount on / or . and see the effect.
1243 
		 */
1244 
		if(!(c->qid.type & QTDIR))
1245 
			error(Enotdir);
1246 
		break;
1247 
 
1248 
	case Amount:
1249 
		/*
1250 
		 * When mounting on an already mounted upon directory,
1251 
		 * one wants subsequent mounts to be attached to the
1252 
		 * original directory, not the replacement.  Don't domount.
1253 
		 */
1254 
		break;
1255 
 
1256 
	case Acreate:
1257 
		/*
1258 
		 * We've already walked all but the last element.
1259 
		 * If the last exists, try to open it OTRUNC.
1260 
		 * If omode&OEXCL is set, just give up.
1261 
		 */
1262 
		e.nelems++;
1263 
		if(walk(&c, e.elems+e.nelems-1, 1, nomount, nil) == 0){
1264 
			if(omode&OEXCL)
1265 
				error(Eexist);
1266 
			omode |= OTRUNC;
1267 
			goto Open;
1268 
		}
1269 
 
1270 
		/*
1271 
		 * The semantics of the create(2) system call are that if the
1272 
		 * file exists and can be written, it is to be opened with truncation.
1273 
		 * On the other hand, the create(5) message fails if the file exists.
1274 
		 * If we get two create(2) calls happening simultaneously,
1275 
		 * they might both get here and send create(5) messages, but only
1276 
		 * one of the messages will succeed.  To provide the expected create(2)
1277 
		 * semantics, the call with the failed message needs to try the above
1278 
		 * walk again, opening for truncation.  This correctly solves the
1279 
		 * create/create race, in the sense that any observable outcome can
1280 
		 * be explained as one happening before the other.
1281 
		 * The create/create race is quite common.  For example, it happens
1282 
		 * when two rc subshells simultaneously update the same
1283 
		 * environment variable.
1284 
		 *
1285 
		 * The implementation still admits a create/create/remove race:
1286 
		 * (A) walk to file, fails
1287 
		 * (B) walk to file, fails
1288 
		 * (A) create file, succeeds, returns
1289 
		 * (B) create file, fails
1290 
		 * (A) remove file, succeeds, returns
1291 
		 * (B) walk to file, return failure.
1292 
		 *
1293 
		 * This is hardly as common as the create/create race, and is really
1294 
		 * not too much worse than what might happen if (B) got a hold of a
1295 
		 * file descriptor and then the file was removed -- either way (B) can't do
1296 
		 * anything with the result of the create call.  So we don't care about this race.
1297 
		 *
1298 
		 * Applications that care about more fine-grained decision of the races
1299 
		 * can use the OEXCL flag to get at the underlying create(5) semantics;
1300 
		 * by default we provide the common case.
1301 
		 *
1302 
		 * We need to stay behind the mount point in case we
1303 
		 * need to do the first walk again (should the create fail).
1304 
		 *
1305 
		 * We also need to cross the mount point and find the directory
1306 
		 * in the union in which we should be creating.
1307 
		 *
1308 
		 * The channel staying behind is c, the one moving forward is cnew.
1309 
		 */
1310 
		m = nil;
1311 
		cnew = nil;	/* is this assignment necessary? */
1312 
		if(!waserror()){	/* try create */
1313 
			if(!nomount && findmount(&cnew, &m, c->type, c->dev, c->qid))
1314 
				cnew = createdir(cnew, m);
1315 
			else{
1316 
				cnew = c;
1317 
				incref(&cnew->ref);
1318 
			}
1319 
 
1320 
			/*
1321 
			 * We need our own copy of the Chan because we're
1322 
			 * about to send a create, which will move it.  Once we have
1323 
			 * our own copy, we can fix the name, which might be wrong
1324 
			 * if findmount gave us a new Chan.
1325 
			 */
1326 
			cnew = cunique(cnew);
1327 
			cnameclose(cnew->name);
1328 
			cnew->name = c->name;
1329 
			incref(&cnew->name->ref);
1330 
 
1331 
			devtab[cnew->type]->create(cnew, e.elems[e.nelems-1], omode&~(OEXCL|OCEXEC), perm);
1332 
			poperror();
1333 
			if(omode & OCEXEC)
1334 
				cnew->flag |= CCEXEC;
1335 
			if(omode & ORCLOSE)
1336 
				cnew->flag |= CRCLOSE;
1337 
			if(m)
1338 
				putmhead(m);
1339 
			cclose(c);
1340 
			c = cnew;
1341 
			c->name = addelem(c->name, e.elems[e.nelems-1]);
1342 
			break;
1343 
		}else{		/* create failed */
1344 
			cclose(cnew);
1345 
			if(m)
1346 
				putmhead(m);
1347 
			if(omode & OEXCL)
1348 
				nexterror();
1349 
			/* save error */
1350 
			createerr = up->errstr;
1351 
			up->errstr = tmperrbuf;
1352 
			/* note: we depend that walk does not error */
1353 
			if(walk(&c, e.elems+e.nelems-1, 1, nomount, nil) < 0){
1354 
				up->errstr = createerr;
1355 
				error(createerr);	/* report true error */
1356 
			}
1357 
			up->errstr = createerr;
1358 
			omode |= OTRUNC;
1359 
			goto Open;
1360 
		}
1361 
		panic("namec: not reached");
1362 
 
1363 
	default:
1364 
		panic("unknown namec access %d\n", amode);
1365 
	}
1366 
 
1367 
	poperror();
1368 
 
1369 
	/* place final element in genbuf for e.g. exec */
1370 
	if(e.nelems > 0)
1371 
		kstrcpy(up->genbuf, e.elems[e.nelems-1], sizeof up->genbuf);
1372 
	else
1373 
		kstrcpy(up->genbuf, ".", sizeof up->genbuf);
1374 
	free(e.name);
1375 
	free(e.elems);
1376 
	free(e.off);
1377 
 
1378 
	return c;
1379 
}
1380 
 
1381 
/*
1382 
 * name is valid. skip leading / and ./ as much as possible
1383 
 */
1384 
char*
1385 
skipslash(char *name)
1386 
{
1387 
	while(name[0]=='/' || (name[0]=='.' && (name[1]==0 || name[1]=='/')))
1388 
		name++;
1389 
	return name;
1390 
}
1391 
 
1392 
char isfrog[256]={
1393 
	/*NUL*/	1, 1, 1, 1, 1, 1, 1, 1,	/* 0 */
1394 
	/*BKS*/	1, 1, 1, 1, 1, 1, 1, 1, /* 0x08 */
1395 
	/*DLE*/	1, 1, 1, 1, 1, 1, 1, 1, /* 0x10 */
1396 
	/*CAN*/	1, 1, 1, 1, 1, 1, 1, 1, /* 0x18 */
1397 
		0, 0, 0, 0, 0, 0, 0, 0, /* 0x20 */
1398 
		0, 0, 0, 0, 0, 0, 0, 1, /* 0x28 (1 is '/', 0x2F) */
1399 
		0, 0, 0, 0, 0, 0, 0, 0, /* 0x30 */
1400 
		0, 0, 0, 0, 0, 0, 0, 0, /* 0x38 */
1401 
		0, 0, 0, 0, 0, 0, 0, 0, /* 0x40 */
1402 
		0, 0, 0, 0, 0, 0, 0, 0, /* 0x48 */
1403 
		0, 0, 0, 0, 0, 0, 0, 0, /* 0x50 */
1404 
		0, 0, 0, 0, 0, 0, 0, 0, /* 0x58 */
1405 
		0, 0, 0, 0, 0, 0, 0, 0, /* 0x60 */
1406 
		0, 0, 0, 0, 0, 0, 0, 0, /* 0x68 */
1407 
		0, 0, 0, 0, 0, 0, 0, 0, /* 0x70 */
1408 
		0, 0, 0, 0, 0, 0, 0, 1, /* 0x78 (1 is DEL, 0x7F) */
1409 
};
1410 
 
1411 
/*
1412 
 * Check that the name
1413 
 *  a) is in valid memory.
1414 
 *  b) is shorter than 2^16 bytes, so it can fit in a 9P string field.
1415 
 *  c) contains no frogs.
1416 
 * The first byte is known to be addressible by the requester, so the
1417 
 * routine works for kernel and user memory both.
1418 
 * The parameter slashok flags whether a slash character is an error
1419 
 * or a valid character.
1420 
 */
1421 
void
1422 
validname(char *aname, int slashok)
1423 
{
1424 
	char *ename, *name;
1425 
	int c;
1426 
	Rune r;
1427 
 
1428 
	name = aname;
1429 
/*
1430 
	if(((ulong)name & KZERO) != KZERO) {
1431 
		p = name;
1432 
		t = BY2PG-((ulong)p&(BY2PG-1));
1433 
		while((ename=vmemchr(p, 0, t)) == nil) {
1434 
			p += t;
1435 
			t = BY2PG;
1436 
		}
1437 
	}else
1438 
*/
1439 
		ename = memchr(name, 0, (1<<16));
1440 
 
1441 
	if(ename==nil || ename-name>=(1<<16))
1442 
		error("name too long");
1443 
 
1444 
	while(*name){
1445 
		/* all characters above '~' are ok */
1446 
		c = *(uchar*)name;
1447 
		if(c >= Runeself)
1448 
			name += chartorune(&r, name);
1449 
		else{
1450 
			if(isfrog[c])
1451 
				if(!slashok || c!='/'){
1452 
					snprint(up->genbuf, sizeof(up->genbuf), "%s: %q", Ebadchar, aname);
1453 
					error(up->genbuf);
1454 
			}
1455 
			name++;
1456 
		}
1457 
	}
1458 
}
1459 
 
1460 
void
1461 
isdir(Chan *c)
1462 
{
1463 
	if(c->qid.type & QTDIR)
1464 
		return;
1465 
	error(Enotdir);
1466 
}
1467 
 
1468 
/*
1469 
 * This is necessary because there are many
1470 
 * pointers to the top of a given mount list:
1471 
 *
1472 
 *	- the mhead in the namespace hash table
1473 
 *	- the mhead in chans returned from findmount:
1474 
 *	  used in namec and then by unionread.
1475 
 *	- the mhead in chans returned from createdir:
1476 
 *	  used in the open/create race protect, which is gone.
1477 
 *
1478 
 * The RWlock in the Mhead protects the mount list it contains.
1479 
 * The mount list is deleted when we cunmount.
1480 
 * The RWlock ensures that nothing is using the mount list at that time.
1481 
 *
1482 
 * It is okay to replace c->mh with whatever you want as
1483 
 * long as you are sure you have a unique reference to it.
1484 
 *
1485 
 * This comment might belong somewhere else.
1486 
 */
1487 
void
1488 
putmhead(Mhead *m)
1489 
{
1490 
	if(m && decref(&m->ref) == 0){
1491 
		m->mount = (Mount*)0xCafeBeef;
1492 
		free(m);
1493 
	}
1494 
}