sys/src/9/port/chan.c

   1 #include        "u.h"
   2 #include        "../port/lib.h"
   3 #include        "mem.h"
   4 #include        "dat.h"
   5 #include        "fns.h"
   6 #include        "../port/error.h"
   7
   8 int chandebug=0;                /* toggled by sysr1 */
   9 #define DBG if(chandebug)iprint
  10
  11 enum
  12 {
  13         PATHSLOP        = 20,
  14         PATHMSLOP       = 20,
  15 };
  16
  17 static struct Chanalloc
  18 {
  19         Lock;
  20         int     fid;
  21         Chan    *free;
  22         Chan    *list;
  23 }chanalloc;
  24
  25 typedef struct Elemlist Elemlist;
  26
  27 struct Elemlist
  28 {
  29         char    *aname; /* original name */
  30         char    *name;  /* copy of name, so '/' can be overwritten */
  31         int     nelems;
  32         char    **elems;
  33         int     *off;
  34         int     mustbedir;
  35         int     nerror;
  36         int     prefix;
  37 };
  38
  39 #define SEP(c) ((c) == 0 || (c) == '/')
  40
  41 static void
  42 dumpmount(void)         /* DEBUGGING */
  43 {
  44         Pgrp *pg;
  45         Mount *t;
  46         Mhead **h, **he, *f;
  47
  48         if(up == nil){
  49                 print("no process for dumpmount\n");
  50                 return;
  51         }
  52         pg = up->pgrp;
  53         if(pg == nil){
  54                 print("no pgrp for dumpmount\n");
  55                 return;
  56         }
  57         rlock(&pg->ns);
  58         if(waserror()){
  59                 runlock(&pg->ns);
  60                 nexterror();
  61         }
  62
  63         he = &pg->mnthash[MNTHASH];
  64         for(h = pg->mnthash; h < he; h++){
  65                 for(f = *h; f; f = f->hash){
  66                         print("head: %#p: %s %#llux.%lud %C %lud -> \n", f,
  67                                 f->from->path->s, f->from->qid.path,
  68                                 f->from->qid.vers, devtab[f->from->type]->dc,
  69                                 f->from->dev);
  70                         for(t = f->mount; t; t = t->next)
  71                                 print("\t%#p: %s (umh %#p) (path %#.8llux dev %C %lud)\n", t, t->to->path->s, t->to->umh, t->to->qid.path, devtab[t->to->type]->dc, t->to->dev);
  72                 }
  73         }
  74         poperror();
  75         runlock(&pg->ns);
  76 }
  77
  78 char*
  79 chanpath(Chan *c)
  80 {
  81         if(c == nil)
  82                 return "<nil chan>";
  83         if(c->path == nil)
  84                 return "<nil path>";
  85         if(c->path->s == nil)
  86                 return "<nil path.s>";
  87         return c->path->s;
  88 }
  89
  90 int
  91 isdotdot(char *p)
  92 {
  93         return p[0]=='.' && p[1]=='.' && p[2]=='\0';
  94 }
  95
  96 long
  97 incref(Ref *r)
  98 {
  99         long x;
 100
 101         lock(r);
 102         x = ++r->ref;
 103         unlock(r);
 104         return x;
 105 }
 106
 107 long
 108 decref(Ref *r)
 109 {
 110         long x;
 111
 112         lock(r);
 113         x = --r->ref;
 114         unlock(r);
 115         if(x < 0)
 116                 panic("decref pc=%#p", getcallerpc(&r));
 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 < ns){
 133                 memmove(s, t, nt);
 134                 s[nt] = '\0';
 135                 return;
 136         }
 137         /* too long, truncate */
 138         nt = ns-1;
 139         memmove(s, t, nt);
 140         s[nt] = '\0';
 141         /* append ... if there is space */
 142         ns -= 4;
 143         if(ns < 0)
 144                 return;
 145         /* look for first byte of UTF-8 sequence by skipping continuation bytes */
 146         while(ns>0 && (s[--ns]&0xC0)==0x80)
 147                 ;
 148         strcpy(s+ns, "...");
 149 }
 150
 151 int
 152 emptystr(char *s)
 153 {
 154         if(s == nil)
 155                 return 1;
 156         if(s[0] == '\0')
 157                 return 1;
 158         return 0;
 159 }
 160
 161 /*
 162  * Atomically replace *p with copy of s
 163  */
 164 void
 165 kstrdup(char **p, char *s)
 166 {
 167         int n;
 168         char *t, *prev;
 169
 170         n = strlen(s);
 171         /* if it's a user, we can wait for memory; if not, something's very wrong */
 172         if(up != nil)
 173                 t = smalloc(n+1);
 174         else{
 175                 t = malloc(n+1);
 176                 if(t == nil)
 177                         panic("kstrdup: no memory");
 178         }
 179         setmalloctag(t, getcallerpc(&p));
 180         memmove(t, s, n);
 181         t[n] = '\0';
 182         prev = *p;
 183         *p = t;
 184         free(prev);
 185 }
 186
 187 void
 188 chandevreset(void)
 189 {
 190         int i;
 191
 192         todinit();      /* avoid later reentry causing infinite recursion */
 193         for(i=0; devtab[i] != nil; i++)
 194                 devtab[i]->reset();
 195 }
 196
 197 void
 198 chandevinit(void)
 199 {
 200         int i;
 201
 202         for(i=0; devtab[i] != nil; i++)
 203                 devtab[i]->init();
 204 }
 205
 206 void
 207 chandevshutdown(void)
 208 {
 209         int i;
 210
 211         /* shutdown in reverse order */
 212         for(i=0; devtab[i] != nil; i++)
 213                 ;
 214         for(i--; i >= 0; i--)
 215                 devtab[i]->shutdown();
 216 }
 217
 218 Chan*
 219 newchan(void)
 220 {
 221         Chan *c;
 222
 223         lock(&chanalloc);
 224         c = chanalloc.free;
 225         if(c != 0){
 226                 chanalloc.free = c->next;
 227                 c->next = 0;
 228         }
 229         unlock(&chanalloc);
 230
 231         if(c == nil){
 232                 c = smalloc(sizeof(Chan));
 233                 lock(&chanalloc);
 234                 c->fid = ++chanalloc.fid;
 235                 c->link = chanalloc.list;
 236                 chanalloc.list = c;
 237                 unlock(&chanalloc);
 238         }
 239
 240         /* if you get an error before associating with a dev,
 241            close calls rootclose, a nop */
 242         c->type = 0;
 243         c->flag = 0;
 244         c->ref = 1;
 245         c->dev = 0;
 246         c->offset = 0;
 247         c->devoffset = 0;
 248         c->iounit = 0;
 249         c->umh = 0;
 250         c->uri = 0;
 251         c->dri = 0;
 252         c->aux = 0;
 253         c->mchan = 0;
 254         c->mcp = 0;
 255         c->mux = 0;
 256         memset(&c->mqid, 0, sizeof(c->mqid));
 257         c->path = 0;
 258         c->ismtpt = 0;
 259
 260         return c;
 261 }
 262
 263 Ref npath;
 264
 265 Path*
 266 newpath(char *s)
 267 {
 268         int i;
 269         Path *p;
 270
 271         p = smalloc(sizeof(Path));
 272         i = strlen(s);
 273         p->len = i;
 274         p->alen = i+PATHSLOP;
 275         p->s = smalloc(p->alen);
 276         memmove(p->s, s, i+1);
 277         p->ref = 1;
 278         incref(&npath);
 279
 280         /*
 281          * Cannot use newpath for arbitrary names because the mtpt
 282          * array will not be populated correctly.  The names #/ and / are
 283          * allowed, but other names with / in them draw warnings.
 284          */
 285         if(strchr(s, '/') && strcmp(s, "#/") != 0 && strcmp(s, "/") != 0)
 286                 print("newpath: %s from %#p\n", s, getcallerpc(&s));
 287
 288         p->mlen = 1;
 289         p->malen = PATHMSLOP;
 290         p->mtpt = smalloc(p->malen*sizeof p->mtpt[0]);
 291         return p;
 292 }
 293
 294 static Path*
 295 copypath(Path *p)
 296 {
 297         int i;
 298         Path *pp;
 299
 300         pp = smalloc(sizeof(Path));
 301         pp->ref = 1;
 302         incref(&npath);
 303         DBG("copypath %s %p => %p\n", p->s, p, pp);
 304
 305         pp->len = p->len;
 306         pp->alen = p->alen;
 307         pp->s = smalloc(p->alen);
 308         memmove(pp->s, p->s, p->len+1);
 309
 310         pp->mlen = p->mlen;
 311         pp->malen = p->malen;
 312         pp->mtpt = smalloc(p->malen*sizeof pp->mtpt[0]);
 313         for(i=0; i<pp->mlen; i++){
 314                 pp->mtpt[i] = p->mtpt[i];
 315                 if(pp->mtpt[i])
 316                         incref(pp->mtpt[i]);
 317         }
 318
 319         return pp;
 320 }
 321
 322 void
 323 pathclose(Path *p)
 324 {
 325         int i;
 326
 327         if(p == nil)
 328                 return;
 329 //XXX
 330         DBG("pathclose %p %s ref=%ld =>", p, p->s, p->ref);
 331         for(i=0; i<p->mlen; i++)
 332                 DBG(" %p", p->mtpt[i]);
 333         DBG("\n");
 334
 335         if(decref(p))
 336                 return;
 337         decref(&npath);
 338         free(p->s);
 339         for(i=0; i<p->mlen; i++)
 340                 if(p->mtpt[i])
 341                         cclose(p->mtpt[i]);
 342         free(p->mtpt);
 343         free(p);
 344 }
 345
 346 /*
 347  * In place, rewrite name to compress multiple /, eliminate ., and process ..
 348  * (Really only called to remove a trailing .. that has been added.
 349  * Otherwise would need to update n->mtpt as well.)
 350  */
 351 static void
 352 fixdotdotname(Path *p)
 353 {
 354         char *r;
 355
 356         if(p->s[0] == '#'){
 357                 r = strchr(p->s, '/');
 358                 if(r == nil)
 359                         return;
 360                 cleanname(r);
 361
 362                 /*
 363                  * The correct name is #i rather than #i/,
 364                  * but the correct name of #/ is #/.
 365                  */
 366                 if(strcmp(r, "/")==0 && p->s[1] != '/')
 367                         *r = '\0';
 368         }else
 369                 cleanname(p->s);
 370         p->len = strlen(p->s);
 371 }
 372
 373 static Path*
 374 uniquepath(Path *p)
 375 {
 376         Path *new;
 377
 378         if(p->ref > 1){
 379                 /* copy on write */
 380                 new = copypath(p);
 381                 pathclose(p);
 382                 p = new;
 383         }
 384         return p;
 385 }
 386
 387 static Path*
 388 addelem(Path *p, char *s, Chan *from)
 389 {
 390         char *t;
 391         int a, i;
 392         Chan *c, **tt;
 393
 394         if(s[0]=='.' && s[1]=='\0')
 395                 return p;
 396
 397         p = uniquepath(p);
 398
 399         i = strlen(s);
 400         if(p->len+1+i+1 > p->alen){
 401                 a = p->len+1+i+1 + PATHSLOP;
 402                 t = smalloc(a);
 403                 memmove(t, p->s, p->len+1);
 404                 free(p->s);
 405                 p->s = t;
 406                 p->alen = a;
 407         }
 408         /* don't insert extra slash if one is present */
 409         if(p->len>0 && p->s[p->len-1]!='/' && s[0]!='/')
 410                 p->s[p->len++] = '/';
 411         memmove(p->s+p->len, s, i+1);
 412         p->len += i;
 413         if(isdotdot(s)){
 414                 fixdotdotname(p);
 415                 DBG("addelem %s .. => rm %p\n", p->s, p->mtpt[p->mlen-1]);
 416                 if(p->mlen>1 && (c = p->mtpt[--p->mlen])){
 417                         p->mtpt[p->mlen] = nil;
 418                         cclose(c);
 419                 }
 420         }else{
 421                 if(p->mlen >= p->malen){
 422                         p->malen = p->mlen+1+PATHMSLOP;
 423                         tt = smalloc(p->malen*sizeof tt[0]);
 424                         memmove(tt, p->mtpt, p->mlen*sizeof tt[0]);
 425                         free(p->mtpt);
 426                         p->mtpt = tt;
 427                 }
 428                 DBG("addelem %s %s => add %p\n", p->s, s, from);
 429                 p->mtpt[p->mlen++] = from;
 430                 if(from)
 431                         incref(from);
 432         }
 433         return p;
 434 }
 435
 436 void
 437 chanfree(Chan *c)
 438 {
 439         c->flag = CFREE;
 440
 441         if(c->dirrock != nil){
 442                 free(c->dirrock);
 443                 c->dirrock = 0;
 444                 c->nrock = 0;
 445                 c->mrock = 0;
 446         }
 447         if(c->umh != nil){
 448                 putmhead(c->umh);
 449                 c->umh = nil;
 450         }
 451         if(c->umc != nil){
 452                 cclose(c->umc);
 453                 c->umc = nil;
 454         }
 455         if(c->mux != nil){
 456                 muxclose(c->mux);
 457                 c->mux = nil;
 458         }
 459         if(c->mchan != nil){
 460                 cclose(c->mchan);
 461                 c->mchan = nil;
 462         }
 463
 464         pathclose(c->path);
 465         c->path = nil;
 466
 467         lock(&chanalloc);
 468         c->next = chanalloc.free;
 469         chanalloc.free = c;
 470         unlock(&chanalloc);
 471 }
 472
 473 /*
 474  * Queue a chan to be closed by one of the clunk procs.
 475  */
 476 struct {
 477         Chan *head;
 478         Chan *tail;
 479         int nqueued;
 480         int nclosed;
 481         Lock l;
 482         QLock q;
 483         Rendez r;
 484 } clunkq;
 485
 486 static int
 487 clunkwork(void*)
 488 {
 489         return clunkq.head != nil;
 490 }
 491
 492 static void
 493 closeproc(void*)
 494 {
 495         Chan *c;
 496
 497         for(;;){
 498                 if(clunkq.head == nil){
 499                         if(!waserror()){
 500                                 tsleep(&clunkq.r, clunkwork, nil, 5000);
 501                                 poperror();
 502                         }
 503                 }
 504                 qunlock(&clunkq.q);
 505                 lock(&clunkq.l);
 506                 c = clunkq.head;
 507                 if(c == nil){
 508                         unlock(&clunkq.l);
 509                         pexit("no work", 1);
 510                 }
 511                 clunkq.head = c->next;
 512                 clunkq.nclosed++;
 513                 unlock(&clunkq.l);
 514                 if(!waserror()){
 515                         devtab[c->type]->close(c);
 516                         poperror();
 517                 }
 518                 chanfree(c);
 519                 qlock(&clunkq.q);
 520         }
 521 }
 522
 523 static void
 524 closechanq(Chan *c)
 525 {
 526         lock(&clunkq.l);
 527         clunkq.nqueued++;
 528         c->next = nil;
 529         if(clunkq.head)
 530                 clunkq.tail->next = c;
 531         else
 532                 clunkq.head = c;
 533         clunkq.tail = c;
 534         unlock(&clunkq.l);
 535
 536         if(up != 0 && palloc.Lock.p != up && canqlock(&clunkq.q)){
 537                 c = up->dot;
 538                 up->dot = nil;
 539                 kproc("closeproc", closeproc, nil);
 540                 up->dot = c;
 541         }else
 542                 wakeup(&clunkq.r);
 543 }
 544
 545 void
 546 cclose(Chan *c)
 547 {
 548         if(c == nil || c->ref < 1 || c->flag&CFREE)
 549                 panic("cclose %#p", getcallerpc(&c));
 550
 551         DBG("cclose %p name=%s ref=%ld\n", c, chanpath(c), c->ref);
 552
 553         if(decref(c))
 554                 return;
 555
 556         if(devtab[c->type]->dc == L'M')
 557         if((c->flag&(CRCLOSE|CCACHE)) == CCACHE)
 558         if((c->qid.type&(QTEXCL|QTMOUNT|QTAUTH)) == 0){
 559                 closechanq(c);
 560                 return;
 561         }
 562
 563         if(!waserror()){
 564                 devtab[c->type]->close(c);
 565                 poperror();
 566         }
 567         chanfree(c);
 568 }
 569
 570 void
 571 ccloseq(Chan *c)
 572 {
 573         if(c == nil || c->ref < 1 || c->flag&CFREE)
 574                 panic("ccloseq %#p", getcallerpc(&c));
 575
 576         DBG("ccloseq %p name=%s ref=%ld\n", c, chanpath(c), c->ref);
 577
 578         if(decref(c))
 579                 return;
 580
 581         closechanq(c);
 582 }
 583
 584 /*
 585  * Make sure we have the only copy of c.  (Copy on write.)
 586  */
 587 Chan*
 588 cunique(Chan *c)
 589 {
 590         Chan *nc;
 591
 592         if(c->ref != 1){
 593                 nc = cclone(c);
 594                 cclose(c);
 595                 c = nc;
 596         }
 597
 598         return c;
 599 }
 600
 601 int
 602 eqqid(Qid a, Qid b)
 603 {
 604         return a.path==b.path && a.vers==b.vers;
 605 }
 606
 607 int
 608 eqchan(Chan *a, Chan *b, int skipvers)
 609 {
 610         if(a->qid.path != b->qid.path)
 611                 return 0;
 612         if(!skipvers && a->qid.vers!=b->qid.vers)
 613                 return 0;
 614         if(a->type != b->type)
 615                 return 0;
 616         if(a->dev != b->dev)
 617                 return 0;
 618         return 1;
 619 }
 620
 621 int
 622 eqchantdqid(Chan *a, int type, int dev, Qid qid, int skipvers)
 623 {
 624         if(a->qid.path != qid.path)
 625                 return 0;
 626         if(!skipvers && a->qid.vers!=qid.vers)
 627                 return 0;
 628         if(a->type != type)
 629                 return 0;
 630         if(a->dev != dev)
 631                 return 0;
 632         return 1;
 633 }
 634
 635 Mhead*
 636 newmhead(Chan *from)
 637 {
 638         Mhead *mh;
 639
 640         mh = smalloc(sizeof(Mhead));
 641         mh->ref = 1;
 642         mh->from = from;
 643         incref(from);
 644         return mh;
 645 }
 646
 647 int
 648 cmount(Chan **newp, Chan *old, int flag, char *spec)
 649 {
 650         int order, flg;
 651         Chan *new;
 652         Mhead *m, **l, *mh;
 653         Mount *nm, *f, *um, **h;
 654         Pgrp *pg;
 655
 656         if(QTDIR & (old->qid.type^(*newp)->qid.type))
 657                 error(Emount);
 658
 659         if(old->umh)
 660                 print("cmount: unexpected umh, caller %#p\n", getcallerpc(&newp));
 661
 662         order = flag&MORDER;
 663
 664         if((old->qid.type&QTDIR)==0 && order != MREPL)
 665                 error(Emount);
 666
 667         new = *newp;
 668         mh = new->umh;
 669
 670         /*
 671          * Not allowed to bind when the old directory is itself a union.
 672          * (Maybe it should be allowed, but I don't see what the semantics
 673          * would be.)
 674          *
 675          * We need to check mh->mount->next to tell unions apart from
 676          * simple mount points, so that things like
 677          *      mount -c fd /root
 678          *      bind -c /root /
 679          * work.
 680          *
 681          * The check of mount->mflag allows things like
 682          *      mount fd /root
 683          *      bind -c /root /
 684          *
 685          * This is far more complicated than it should be, but I don't
 686          * see an easier way at the moment.
 687          */
 688         if((flag&MCREATE) && mh && mh->mount
 689         && (mh->mount->next || !(mh->mount->mflag&MCREATE)))
 690                 error(Emount);
 691
 692         pg = up->pgrp;
 693         wlock(&pg->ns);
 694
 695         l = &MOUNTH(pg, old->qid);
 696         for(m = *l; m; m = m->hash){
 697                 if(eqchan(m->from, old, 1))
 698                         break;
 699                 l = &m->hash;
 700         }
 701
 702         if(m == nil){
 703                 /*
 704                  *  nothing mounted here yet.  create a mount
 705                  *  head and add to the hash table.
 706                  */
 707                 m = newmhead(old);
 708                 *l = m;
 709
 710                 /*
 711                  *  if this is a union mount, add the old
 712                  *  node to the mount chain.
 713                  */
 714                 if(order != MREPL)
 715                         m->mount = newmount(m, old, 0, 0);
 716         }
 717         wlock(&m->lock);
 718         if(waserror()){
 719                 wunlock(&m->lock);
 720                 nexterror();
 721         }
 722         wunlock(&pg->ns);
 723
 724         nm = newmount(m, new, flag, spec);
 725         if(mh != nil && mh->mount != nil){
 726                 /*
 727                  *  copy a union when binding it onto a directory
 728                  */
 729                 flg = order;
 730                 if(order == MREPL)
 731                         flg = MAFTER;
 732                 h = &nm->next;
 733                 um = mh->mount;
 734                 for(um = um->next; um; um = um->next){
 735                         f = newmount(m, um->to, flg, um->spec);
 736                         *h = f;
 737                         h = &f->next;
 738                 }
 739         }
 740
 741         if(m->mount && order == MREPL){
 742                 mountfree(m->mount);
 743                 m->mount = 0;
 744         }
 745
 746         if(flag & MCREATE)
 747                 nm->mflag |= MCREATE;
 748
 749         if(m->mount && order == MAFTER){
 750                 for(f = m->mount; f->next; f = f->next)
 751                         ;
 752                 f->next = nm;
 753         }else{
 754                 for(f = nm; f->next; f = f->next)
 755                         ;
 756                 f->next = m->mount;
 757                 m->mount = nm;
 758         }
 759
 760         wunlock(&m->lock);
 761         poperror();
 762         return nm->mountid;
 763 }
 764
 765 void
 766 cunmount(Chan *mnt, Chan *mounted)
 767 {
 768         Pgrp *pg;
 769         Mhead *m, **l;
 770         Mount *f, **p;
 771
 772         if(mnt->umh)    /* should not happen */
 773                 print("cunmount newp extra umh %p has %p\n", mnt, mnt->umh);
 774
 775         /*
 776          * It _can_ happen that mounted->umh is non-nil,
 777          * because mounted is the result of namec(Aopen)
 778          * (see sysfile.c:/^sysunmount).
 779          * If we open a union directory, it will have a umh.
 780          * Although surprising, this is okay, since the
 781          * cclose will take care of freeing the umh.
 782          */
 783
 784         pg = up->pgrp;
 785         wlock(&pg->ns);
 786
 787         l = &MOUNTH(pg, mnt->qid);
 788         for(m = *l; m; m = m->hash){
 789                 if(eqchan(m->from, mnt, 1))
 790                         break;
 791                 l = &m->hash;
 792         }
 793
 794         if(m == 0){
 795                 wunlock(&pg->ns);
 796                 error(Eunmount);
 797         }
 798
 799         wlock(&m->lock);
 800         if(mounted == 0){
 801                 *l = m->hash;
 802                 wunlock(&pg->ns);
 803                 mountfree(m->mount);
 804                 m->mount = nil;
 805                 cclose(m->from);
 806                 wunlock(&m->lock);
 807                 putmhead(m);
 808                 return;
 809         }
 810
 811         p = &m->mount;
 812         for(f = *p; f; f = f->next){
 813                 /* BUG: Needs to be 2 pass */
 814                 if(eqchan(f->to, mounted, 1) ||
 815                   (f->to->mchan && eqchan(f->to->mchan, mounted, 1))){
 816                         *p = f->next;
 817                         f->next = 0;
 818                         mountfree(f);
 819                         if(m->mount == nil){
 820                                 *l = m->hash;
 821                                 cclose(m->from);
 822                                 wunlock(&m->lock);
 823                                 wunlock(&pg->ns);
 824                                 putmhead(m);
 825                                 return;
 826                         }
 827                         wunlock(&m->lock);
 828                         wunlock(&pg->ns);
 829                         return;
 830                 }
 831                 p = &f->next;
 832         }
 833         wunlock(&m->lock);
 834         wunlock(&pg->ns);
 835         error(Eunion);
 836 }
 837
 838 Chan*
 839 cclone(Chan *c)
 840 {
 841         Chan *nc;
 842         Walkqid *wq;
 843
 844         if(c == nil || c->ref < 1 || c->flag&CFREE)
 845                 panic("cclone: %#p", getcallerpc(&c));
 846         wq = devtab[c->type]->walk(c, nil, nil, 0);
 847         if(wq == nil)
 848                 error("clone failed");
 849         nc = wq->clone;
 850         free(wq);
 851         nc->path = c->path;
 852         if(c->path)
 853                 incref(c->path);
 854         return nc;
 855 }
 856
 857 /* also used by sysfile.c:/^mountfix */
 858 int
 859 findmount(Chan **cp, Mhead **mp, int type, int dev, Qid qid)
 860 {
 861         Pgrp *pg;
 862         Mhead *m;
 863
 864         pg = up->pgrp;
 865         rlock(&pg->ns);
 866         for(m = MOUNTH(pg, qid); m; m = m->hash){
 867                 rlock(&m->lock);
 868                 if(m->from == nil){
 869                         print("m %p m->from 0\n", m);
 870                         runlock(&m->lock);
 871                         continue;
 872                 }
 873                 if(eqchantdqid(m->from, type, dev, qid, 1)){
 874                         runlock(&pg->ns);
 875                         if(mp != nil){
 876                                 incref(m);
 877                                 if(*mp != nil)
 878                                         putmhead(*mp);
 879                                 *mp = m;
 880                         }
 881                         if(*cp != nil)
 882                                 cclose(*cp);
 883                         incref(m->mount->to);
 884                         *cp = m->mount->to;
 885                         runlock(&m->lock);
 886                         return 1;
 887                 }
 888                 runlock(&m->lock);
 889         }
 890
 891         runlock(&pg->ns);
 892         return 0;
 893 }
 894
 895 /*
 896  * Calls findmount but also updates path.
 897  */
 898 static int
 899 domount(Chan **cp, Mhead **mp, Path **path)
 900 {
 901         Chan **lc;
 902         Path *p;
 903
 904         if(findmount(cp, mp, (*cp)->type, (*cp)->dev, (*cp)->qid) == 0)
 905                 return 0;
 906
 907         if(path){
 908                 p = *path;
 909                 p = uniquepath(p);
 910                 if(p->mlen <= 0)
 911                         print("domount: path %s has mlen==%d\n", p->s, p->mlen);
 912                 else{
 913                         lc = &p->mtpt[p->mlen-1];
 914 DBG("domount %p %s => add %p (was %p)\n", p, p->s, (*mp)->from, p->mtpt[p->mlen-1]);
 915                         incref((*mp)->from);
 916                         if(*lc)
 917                                 cclose(*lc);
 918                         *lc = (*mp)->from;
 919                 }
 920                 *path = p;
 921         }
 922         return 1;
 923 }
 924
 925 /*
 926  * If c is the right-hand-side of a mount point, returns the left hand side.
 927  * Changes name to reflect the fact that we've uncrossed the mountpoint,
 928  * so name had better be ours to change!
 929  */
 930 static Chan*
 931 undomount(Chan *c, Path *path)
 932 {
 933         Chan *nc;
 934
 935         if(path->ref != 1 || path->mlen == 0)
 936                 print("undomount: path %s ref %ld mlen %d caller %#p\n",
 937                         path->s, path->ref, path->mlen, getcallerpc(&c));
 938
 939         if(path->mlen>0 && (nc=path->mtpt[path->mlen-1]) != nil){
 940 DBG("undomount %p %s => remove %p\n", path, path->s, nc);
 941                 cclose(c);
 942                 path->mtpt[path->mlen-1] = nil;
 943                 c = nc;
 944         }
 945         return c;
 946 }
 947
 948 /*
 949  * Call dev walk but catch errors.
 950  */
 951 static Walkqid*
 952 ewalk(Chan *c, Chan *nc, char **name, int nname)
 953 {
 954         Walkqid *wq;
 955
 956         if(waserror())
 957                 return nil;
 958         wq = devtab[c->type]->walk(c, nc, name, nname);
 959         poperror();
 960         return wq;
 961 }
 962
 963 /*
 964  * Either walks all the way or not at all.  No partial results in *cp.
 965  * *nerror is the number of names to display in an error message.
 966  */
 967 static char Edoesnotexist[] = "does not exist";
 968 int
 969 walk(Chan **cp, char **names, int nnames, int nomount, int *nerror)
 970 {
 971         int dev, didmount, dotdot, i, n, nhave, ntry, type;
 972         Chan *c, *nc, *mtpt;
 973         Path *path;
 974         Mhead *mh, *nmh;
 975         Mount *f;
 976         Walkqid *wq;
 977
 978         c = *cp;
 979         incref(c);
 980         path = c->path;
 981         incref(path);
 982         mh = nil;
 983
 984         /*
 985          * While we haven't gotten all the way down the path:
 986          *    1. step through a mount point, if any
 987          *    2. send a walk request for initial dotdot or initial prefix without dotdot
 988          *    3. move to the first mountpoint along the way.
 989          *    4. repeat.
 990          *
 991          * Each time through the loop:
 992          *
 993          *      If didmount==0, c is on the undomount side of the mount point.
 994          *      If didmount==1, c is on the domount side of the mount point.
 995          *      Either way, c's full path is path.
 996          */
 997         didmount = 0;
 998         for(nhave=0; nhave<nnames; nhave+=n){
 999                 if((c->qid.type&QTDIR)==0){
1000                         if(nerror)
1001                                 *nerror = nhave;
1002                         pathclose(path);
1003                         cclose(c);
1004                         kstrcpy(up->errstr, Enotdir, ERRMAX);
1005                         if(mh != nil)
1006                                 putmhead(mh);
1007                         return -1;
1008                 }
1009                 ntry = nnames - nhave;
1010                 if(ntry > MAXWELEM)
1011                         ntry = MAXWELEM;
1012                 dotdot = 0;
1013                 for(i=0; i<ntry; i++){
1014                         if(isdotdot(names[nhave+i])){
1015                                 if(i==0){
1016                                         dotdot = 1;
1017                                         ntry = 1;
1018                                 }else
1019                                         ntry = i;
1020                                 break;
1021                         }
1022                 }
1023
1024                 if(!dotdot && !nomount && !didmount)
1025                         domount(&c, &mh, &path);
1026
1027                 type = c->type;
1028                 dev = c->dev;
1029
1030                 if((wq = ewalk(c, nil, names+nhave, ntry)) == nil){
1031                         /* try a union mount, if any */
1032                         if(mh && !nomount){
1033                                 /*
1034                                  * mh->mount->to == c, so start at mh->mount->next
1035                                  */
1036                                 rlock(&mh->lock);
1037                                 if((f = mh->mount) != nil)
1038                                         f = f->next;
1039                                 for(; f != nil; f = f->next)
1040                                         if((wq = ewalk(f->to, nil, names+nhave, ntry)) != nil){
1041                                                 type = f->to->type;
1042                                                 dev = f->to->dev;
1043                                                 break;
1044                                         }
1045                                 runlock(&mh->lock);
1046                         }
1047                         if(wq == nil){
1048                                 cclose(c);
1049                                 pathclose(path);
1050                                 if(nerror)
1051                                         *nerror = nhave+1;
1052                                 if(mh != nil)
1053                                         putmhead(mh);
1054                                 return -1;
1055                         }
1056                 }
1057
1058                 didmount = 0;
1059                 if(dotdot){
1060                         assert(wq->nqid == 1);
1061                         assert(wq->clone != nil);
1062
1063                         path = addelem(path, "..", nil);
1064                         nc = undomount(wq->clone, path);
1065                         nmh = nil;
1066                         n = 1;
1067                 }else{
1068                         nc = nil;
1069                         nmh = nil;
1070                         if(!nomount){
1071                                 for(i=0; i<wq->nqid && i<ntry-1; i++){
1072                                         if(findmount(&nc, &nmh, type, dev, wq->qid[i])){
1073                                                 didmount = 1;
1074                                                 break;
1075                                         }
1076                                 }
1077                         }
1078                         if(nc == nil){  /* no mount points along path */
1079                                 if(wq->clone == nil){
1080                                         cclose(c);
1081                                         pathclose(path);
1082                                         if(wq->nqid==0 || (wq->qid[wq->nqid-1].type&QTDIR)){
1083                                                 if(nerror)
1084                                                         *nerror = nhave+wq->nqid+1;
1085                                                 kstrcpy(up->errstr, Edoesnotexist, ERRMAX);
1086                                         }else{
1087                                                 if(nerror)
1088                                                         *nerror = nhave+wq->nqid;
1089                                                 kstrcpy(up->errstr, Enotdir, ERRMAX);
1090                                         }
1091                                         free(wq);
1092                                         if(mh != nil)
1093                                                 putmhead(mh);
1094                                         return -1;
1095                                 }
1096                                 n = wq->nqid;
1097                                 nc = wq->clone;
1098                         }else{          /* stopped early, at a mount point */
1099                                 didmount = 1;
1100                                 if(wq->clone != nil){
1101                                         cclose(wq->clone);
1102                                         wq->clone = nil;
1103                                 }
1104                                 n = i+1;
1105                         }
1106                         for(i=0; i<n; i++){
1107                                 mtpt = nil;
1108                                 if(i==n-1 && nmh)
1109                                         mtpt = nmh->from;
1110                                 path = addelem(path, names[nhave+i], mtpt);
1111                         }
1112                 }
1113                 cclose(c);
1114                 c = nc;
1115                 putmhead(mh);
1116                 mh = nmh;
1117                 free(wq);
1118         }
1119
1120         putmhead(mh);
1121
1122         c = cunique(c);
1123
1124         if(c->umh != nil){      //BUG
1125                 print("walk umh\n");
1126                 putmhead(c->umh);
1127                 c->umh = nil;
1128         }
1129
1130         pathclose(c->path);
1131         c->path = path;
1132
1133         cclose(*cp);
1134         *cp = c;
1135         if(nerror)
1136                 *nerror = nhave;
1137         return 0;
1138 }
1139
1140 /*
1141  * c is a mounted non-creatable directory.  find a creatable one.
1142  */
1143 Chan*
1144 createdir(Chan *c, Mhead *m)
1145 {
1146         Chan *nc;
1147         Mount *f;
1148
1149         rlock(&m->lock);
1150         if(waserror()){
1151                 runlock(&m->lock);
1152                 nexterror();
1153         }
1154         for(f = m->mount; f; f = f->next){
1155                 if(f->mflag&MCREATE){
1156                         nc = cclone(f->to);
1157                         runlock(&m->lock);
1158                         poperror();
1159                         cclose(c);
1160                         return nc;
1161                 }
1162         }
1163         error(Enocreate);
1164         return 0;
1165 }
1166
1167 void
1168 saveregisters(void)
1169 {
1170 }
1171
1172 static void
1173 growparse(Elemlist *e)
1174 {
1175         char **new;
1176         int *inew;
1177         enum { Delta = 8 };
1178
1179         if(e->nelems % Delta == 0){
1180                 new = smalloc((e->nelems+Delta) * sizeof(char*));
1181                 memmove(new, e->elems, e->nelems*sizeof(char*));
1182                 free(e->elems);
1183                 e->elems = new;
1184                 inew = smalloc((e->nelems+Delta+1) * sizeof(int));
1185                 memmove(inew, e->off, (e->nelems+1)*sizeof(int));
1186                 free(e->off);
1187                 e->off = inew;
1188         }
1189 }
1190
1191 /*
1192  * The name is known to be valid.
1193  * Copy the name so slashes can be overwritten.
1194  * An empty string will set nelem=0.
1195  * A path ending in / or /. or /.//./ etc. will have
1196  * e.mustbedir = 1, so that we correctly
1197  * reject, e.g., "/adm/users/." when /adm/users is a file
1198  * rather than a directory.
1199  */
1200 static void
1201 parsename(char *aname, Elemlist *e)
1202 {
1203         char *name, *slash;
1204
1205         kstrdup(&e->name, aname);
1206         name = e->name;
1207         e->nelems = 0;
1208         e->elems = nil;
1209         e->off = smalloc(sizeof(int));
1210         e->off[0] = skipslash(name) - name;
1211         for(;;){
1212                 name = skipslash(name);
1213                 if(*name == '\0'){
1214                         e->off[e->nelems] = name+strlen(name) - e->name;
1215                         e->mustbedir = 1;
1216                         break;
1217                 }
1218                 growparse(e);
1219                 e->elems[e->nelems++] = name;
1220                 slash = utfrune(name, '/');
1221                 if(slash == nil){
1222                         e->off[e->nelems] = name+strlen(name) - e->name;
1223                         e->mustbedir = 0;
1224                         break;
1225                 }
1226                 e->off[e->nelems] = slash - e->name;
1227                 *slash++ = '\0';
1228                 name = slash;
1229         }
1230
1231         if(0 && chandebug){
1232                 int i;
1233
1234                 print("parsename %s:", e->name);
1235                 for(i=0; i<=e->nelems; i++)
1236                         print(" %d", e->off[i]);
1237                 print("\n");
1238         }
1239 }
1240
1241 void*
1242 memrchr(void *va, int c, long n)
1243 {
1244         uchar *a, *e;
1245
1246         a = va;
1247         for(e=a+n-1; e>a; e--)
1248                 if(*e == c)
1249                         return e;
1250         return nil;
1251 }
1252
1253 void
1254 namelenerror(char *aname, int len, char *err)
1255 {
1256         char *ename, *name, *next;
1257         int i, errlen;
1258
1259         /*
1260          * If the name is short enough, just use the whole thing.
1261          */
1262         errlen = strlen(err);
1263         if(len < ERRMAX/3 || len+errlen < 2*ERRMAX/3)
1264                 snprint(up->genbuf, sizeof up->genbuf, "%.*s",
1265                         utfnlen(aname, len), aname);
1266         else{
1267                 /*
1268                  * Print a suffix of the name, but try to get a little info.
1269                  */
1270                 ename = aname+len;
1271                 next = ename;
1272                 do{
1273                         name = next;
1274                         next = memrchr(aname, '/', name-aname);
1275                         if(next == nil)
1276                                 next = aname;
1277                         len = ename-next;
1278                 }while(len < ERRMAX/3 || len + errlen < 2*ERRMAX/3);
1279
1280                 /*
1281                  * If the name is ridiculously long, chop it.
1282                  */
1283                 if(name == ename){
1284                         name = ename-ERRMAX/4;
1285                         if(name <= aname)
1286                                 panic("bad math in namelenerror");
1287                         /* walk out of current UTF sequence */
1288                         for(i=0; (*name&0xC0)==0x80 && i<UTFmax; i++)
1289                                 name++;
1290                 }
1291                 snprint(up->genbuf, sizeof up->genbuf, "...%.*s",
1292                         utfnlen(name, ename-name), name);
1293         }
1294         snprint(up->errstr, ERRMAX, "%#q %s", up->genbuf, err);
1295         nexterror();
1296 }
1297
1298 void
1299 nameerror(char *name, char *err)
1300 {
1301         namelenerror(name, strlen(name), err);
1302 }
1303
1304 /*
1305  * Turn a name into a channel.
1306  * &name[0] is known to be a valid address.  It may be a kernel address.
1307  *
1308  * Opening with amode Aopen, Acreate, Aremove, or Aaccess guarantees
1309  * that the result will be the only reference to that particular fid.
1310  * This is necessary since we might pass the result to
1311  * devtab[]->remove().
1312  *
1313  * Opening Atodir or Amount does not guarantee this.
1314  *
1315  * Under certain circumstances, opening Aaccess will cause
1316  * an unnecessary clone in order to get a cunique Chan so it
1317  * can attach the correct name.  Sysstat and sys_stat need the
1318  * correct name so they can rewrite the stat info.
1319  */
1320 Chan*
1321 namec(char *aname, int amode, int omode, ulong perm)
1322 {
1323         int len, n, t, nomount;
1324         Chan *c, *cnew;
1325         Path *path;
1326         Elemlist e;
1327         Rune r;
1328         Mhead *m;
1329         char *createerr, tmperrbuf[ERRMAX];
1330         char *name;
1331
1332         if(aname[0] == '\0')
1333                 error("empty file name");
1334         aname = validnamedup(aname, 1);
1335         if(waserror()){
1336                 free(aname);
1337                 nexterror();
1338         }
1339         DBG("namec %s %d %d\n", aname, amode, omode);
1340         name = aname;
1341
1342         /*
1343          * Find the starting off point (the current slash, the root of
1344          * a device tree, or the current dot) as well as the name to
1345          * evaluate starting there.
1346          */
1347         nomount = 0;
1348         switch(name[0]){
1349         case '/':
1350                 c = up->slash;
1351                 incref(c);
1352                 break;
1353
1354         case '#':
1355                 nomount = 1;
1356                 up->genbuf[0] = '\0';
1357                 n = 0;
1358                 while(*name != '\0' && (*name != '/' || n < 2)){
1359                         if(n >= sizeof(up->genbuf)-1)
1360                                 error(Efilename);
1361                         up->genbuf[n++] = *name++;
1362                 }
1363                 up->genbuf[n] = '\0';
1364                 /*
1365                  *  noattach is sandboxing.
1366                  *
1367                  *  the OK exceptions are:
1368                  *      |  it only gives access to pipes you create
1369                  *      d  this process's file descriptors
1370                  *      e  this process's environment
1371                  *  the iffy exceptions are:
1372                  *      c  time and pid, but also cons and consctl
1373                  *      p  control of your own processes (and unfortunately
1374                  *         any others left unprotected)
1375                  */
1376                 n = chartorune(&r, up->genbuf+1)+1;
1377                 /* actually / is caught by parsing earlier */
1378                 if(utfrune("M", r))
1379                         error(Enoattach);
1380                 if(up->pgrp->noattach && utfrune("|decp", r)==nil)
1381                         error(Enoattach);
1382                 t = devno(r, 1);
1383                 if(t == -1)
1384                         error(Ebadsharp);
1385                 c = devtab[t]->attach(up->genbuf+n);
1386                 break;
1387
1388         default:
1389                 c = up->dot;
1390                 incref(c);
1391                 break;
1392         }
1393
1394         e.aname = aname;
1395         e.prefix = name - aname;
1396         e.name = nil;
1397         e.elems = nil;
1398         e.off = nil;
1399         e.nelems = 0;
1400         e.nerror = 0;
1401         if(waserror()){
1402                 cclose(c);
1403                 free(e.name);
1404                 free(e.elems);
1405                 /*
1406                  * Prepare nice error, showing first e.nerror elements of name.
1407                  */
1408                 if(e.nerror == 0)
1409                         nexterror();
1410                 strcpy(tmperrbuf, up->errstr);
1411                 if(e.off[e.nerror]==0)
1412                         print("nerror=%d but off=%d\n",
1413                                 e.nerror, e.off[e.nerror]);
1414                 if(0 && chandebug)
1415                         print("showing %d+%d/%d (of %d) of %s (%d %d)\n", e.prefix, e.off[e.nerror], e.nerror, e.nelems, aname, e.off[0], e.off[1]);
1416                 len = e.prefix+e.off[e.nerror];
1417                 free(e.off);
1418                 namelenerror(aname, len, tmperrbuf);
1419         }
1420
1421         /*
1422          * Build a list of elements in the name.
1423          */
1424         parsename(name, &e);
1425
1426         /*
1427          * On create, ....
1428          */
1429         if(amode == Acreate){
1430                 /* perm must have DMDIR if last element is / or /. */
1431                 if(e.mustbedir && !(perm&DMDIR)){
1432                         e.nerror = e.nelems;
1433                         error("create without DMDIR");
1434                 }
1435
1436                 /* don't try to walk the last path element just yet. */
1437                 if(e.nelems == 0)
1438                         error(Eexist);
1439                 e.nelems--;
1440         }
1441
1442         if(walk(&c, e.elems, e.nelems, nomount, &e.nerror) < 0){
1443                 if(e.nerror < 0 || e.nerror > e.nelems){
1444                         print("namec %s walk error nerror=%d\n", aname, e.nerror);
1445                         e.nerror = 0;
1446                 }
1447                 nexterror();
1448         }
1449
1450         if(e.mustbedir && !(c->qid.type&QTDIR))
1451                 error("not a directory");
1452
1453         if(amode == Aopen && (omode&3) == OEXEC && (c->qid.type&QTDIR))
1454                 error("cannot exec directory");
1455
1456         switch(amode){
1457         case Abind:
1458                 /* no need to maintain path - cannot dotdot an Abind */
1459                 m = nil;
1460                 if(!nomount)
1461                         domount(&c, &m, nil);
1462                 if(c->umh != nil)
1463                         putmhead(c->umh);
1464                 c->umh = m;
1465                 break;
1466
1467         case Aaccess:
1468         case Aremove:
1469         case Aopen:
1470         Open:
1471                 /* save&update the name; domount might change c */
1472                 path = c->path;
1473                 incref(path);
1474                 m = nil;
1475                 if(!nomount)
1476                         domount(&c, &m, &path);
1477
1478                 /* our own copy to open or remove */
1479                 c = cunique(c);
1480
1481                 /* now it's our copy anyway, we can put the name back */
1482                 pathclose(c->path);
1483                 c->path = path;
1484
1485                 /* record whether c is on a mount point */
1486                 c->ismtpt = m!=nil;
1487
1488                 switch(amode){
1489                 case Aaccess:
1490                 case Aremove:
1491                         putmhead(m);
1492                         break;
1493
1494                 case Aopen:
1495                 case Acreate:
1496 if(c->umh != nil){
1497         print("cunique umh Open\n");
1498         putmhead(c->umh);
1499         c->umh = nil;
1500 }
1501                         /* only save the mount head if it's a multiple element union */
1502                         if(m && m->mount && m->mount->next)
1503                                 c->umh = m;
1504                         else
1505                                 putmhead(m);
1506
1507                         /* save registers else error() in open has wrong value of c saved */
1508                         saveregisters();
1509
1510                         c = devtab[c->type]->open(c, omode&~OCEXEC);
1511
1512                         if(omode & OCEXEC)
1513                                 c->flag |= CCEXEC;
1514                         if(omode & ORCLOSE)
1515                                 c->flag |= CRCLOSE;
1516                         break;
1517                 }
1518                 break;
1519
1520         case Atodir:
1521                 /*
1522                  * Directories (e.g. for cd) are left before the mount point,
1523                  * so one may mount on / or . and see the effect.
1524                  */
1525                 if(!(c->qid.type & QTDIR))
1526                         error(Enotdir);
1527                 break;
1528
1529         case Amount:
1530                 /*
1531                  * When mounting on an already mounted upon directory,
1532                  * one wants subsequent mounts to be attached to the
1533                  * original directory, not the replacement.  Don't domount.
1534                  */
1535                 break;
1536
1537         case Acreate:
1538                 /*
1539                  * We've already walked all but the last element.
1540                  * If the last exists, try to open it OTRUNC.
1541                  * If omode&OEXCL is set, just give up.
1542                  */
1543                 e.nelems++;
1544                 e.nerror++;
1545                 if(walk(&c, e.elems+e.nelems-1, 1, nomount, nil) == 0){
1546                         if(omode&OEXCL)
1547                                 error(Eexist);
1548                         omode |= OTRUNC;
1549                         goto Open;
1550                 }
1551
1552                 /*
1553                  * The semantics of the create(2) system call are that if the
1554                  * file exists and can be written, it is to be opened with truncation.
1555                  * On the other hand, the create(5) message fails if the file exists.
1556                  * If we get two create(2) calls happening simultaneously,
1557                  * they might both get here and send create(5) messages, but only
1558                  * one of the messages will succeed.  To provide the expected create(2)
1559                  * semantics, the call with the failed message needs to try the above
1560                  * walk again, opening for truncation.  This correctly solves the
1561                  * create/create race, in the sense that any observable outcome can
1562                  * be explained as one happening before the other.
1563                  * The create/create race is quite common.  For example, it happens
1564                  * when two rc subshells simultaneously update the same
1565                  * environment variable.
1566                  *
1567                  * The implementation still admits a create/create/remove race:
1568                  * (A) walk to file, fails
1569                  * (B) walk to file, fails
1570                  * (A) create file, succeeds, returns
1571                  * (B) create file, fails
1572                  * (A) remove file, succeeds, returns
1573                  * (B) walk to file, return failure.
1574                  *
1575                  * This is hardly as common as the create/create race, and is really
1576                  * not too much worse than what might happen if (B) got a hold of a
1577                  * file descriptor and then the file was removed -- either way (B) can't do
1578                  * anything with the result of the create call.  So we don't care about this race.
1579                  *
1580                  * Applications that care about more fine-grained decision of the races
1581                  * can use the OEXCL flag to get at the underlying create(5) semantics;
1582                  * by default we provide the common case.
1583                  *
1584                  * We need to stay behind the mount point in case we
1585                  * need to do the first walk again (should the create fail).
1586                  *
1587                  * We also need to cross the mount point and find the directory
1588                  * in the union in which we should be creating.
1589                  *
1590                  * The channel staying behind is c, the one moving forward is cnew.
1591                  */
1592                 m = nil;
1593                 cnew = nil;     /* is this assignment necessary? */
1594                 if(!waserror()){        /* try create */
1595                         if(!nomount && findmount(&cnew, &m, c->type, c->dev, c->qid))
1596                                 cnew = createdir(cnew, m);
1597                         else{
1598                                 cnew = c;
1599                                 incref(cnew);
1600                         }
1601
1602                         /*
1603                          * We need our own copy of the Chan because we're
1604                          * about to send a create, which will move it.  Once we have
1605                          * our own copy, we can fix the name, which might be wrong
1606                          * if findmount gave us a new Chan.
1607                          */
1608                         cnew = cunique(cnew);
1609                         pathclose(cnew->path);
1610                         cnew->path = c->path;
1611                         incref(cnew->path);
1612
1613                         cnew = devtab[cnew->type]->create(cnew, e.elems[e.nelems-1], omode&~(OEXCL|OCEXEC), perm);
1614                         poperror();
1615                         if(omode & OCEXEC)
1616                                 cnew->flag |= CCEXEC;
1617                         if(omode & ORCLOSE)
1618                                 cnew->flag |= CRCLOSE;
1619                         if(m)
1620                                 putmhead(m);
1621                         cclose(c);
1622                         c = cnew;
1623                         c->path = addelem(c->path, e.elems[e.nelems-1], nil);
1624                         break;
1625                 }
1626
1627                 /* create failed */
1628                 cclose(cnew);
1629                 if(m)
1630                         putmhead(m);
1631                 if(omode & OEXCL)
1632                         nexterror();
1633                 /* save error */
1634                 createerr = up->errstr;
1635                 up->errstr = tmperrbuf;
1636                 /* note: we depend that walk does not error */
1637                 if(walk(&c, e.elems+e.nelems-1, 1, nomount, nil) < 0){
1638                         up->errstr = createerr;
1639                         error(createerr);       /* report true error */
1640                 }
1641                 up->errstr = createerr;
1642                 omode |= OTRUNC;
1643                 goto Open;
1644
1645         default:
1646                 panic("unknown namec access %d", amode);
1647         }
1648
1649         /* place final element in genbuf for e.g. exec */
1650         if(e.nelems > 0)
1651                 kstrcpy(up->genbuf, e.elems[e.nelems-1], sizeof up->genbuf);
1652         else
1653                 kstrcpy(up->genbuf, ".", sizeof up->genbuf);
1654         free(e.name);
1655         free(e.elems);
1656         free(e.off);
1657         poperror();     /* e c */
1658         free(aname);
1659         poperror();     /* aname */
1660
1661         return c;
1662 }
1663
1664 /*
1665  * name is valid. skip leading / and ./ as much as possible
1666  */
1667 char*
1668 skipslash(char *name)
1669 {
1670         while(name[0]=='/' || (name[0]=='.' && (name[1]==0 || name[1]=='/')))
1671                 name++;
1672         return name;
1673 }
1674
1675 char isfrog[256]={
1676         /*NUL*/ 1, 1, 1, 1, 1, 1, 1, 1,
1677         /*BKS*/ 1, 1, 1, 1, 1, 1, 1, 1,
1678         /*DLE*/ 1, 1, 1, 1, 1, 1, 1, 1,
1679         /*CAN*/ 1, 1, 1, 1, 1, 1, 1, 1,
1680         ['/']   1,
1681         [0x7f]  1,
1682 };
1683
1684 /*
1685  * Check that the name
1686  *  a) is in valid memory.
1687  *  b) is shorter than 2^16 bytes, so it can fit in a 9P string field.
1688  *  c) contains no frogs.
1689  * The first byte is known to be addressible by the requester, so the
1690  * routine works for kernel and user memory both.
1691  * The parameter slashok flags whether a slash character is an error
1692  * or a valid character.
1693  *
1694  * The parameter dup flags whether the string should be copied
1695  * out of user space before being scanned the second time.
1696  * (Otherwise a malicious thread could remove the NUL, causing us
1697  * to access unchecked addresses.)
1698  */
1699 static char*
1700 validname0(char *aname, int slashok, int dup, ulong pc)
1701 {
1702         char *ename, *name, *s;
1703         int c, n;
1704         Rune r;
1705
1706         name = aname;
1707         if((ulong)name < KZERO){
1708                 if(!dup)
1709                         print("warning: validname called from %#p with user pointer", pc);
1710                 ename = vmemchr(name, 0, (1<<16));
1711         }else
1712                 ename = memchr(name, 0, (1<<16));
1713
1714         if(ename==nil || ename-name>=(1<<16))
1715                 error("name too long");
1716
1717         s = nil;
1718         if(dup){
1719                 n = ename-name;
1720                 s = smalloc(n+1);
1721                 memmove(s, name, n);
1722                 s[n] = 0;
1723                 aname = s;
1724                 name = s;
1725                 setmalloctag(s, pc);
1726         }
1727
1728         while(*name){
1729                 /* all characters above '~' are ok */
1730                 c = *(uchar*)name;
1731                 if(c >= Runeself)
1732                         name += chartorune(&r, name);
1733                 else{
1734                         if(isfrog[c])
1735                                 if(!slashok || c!='/'){
1736                                         snprint(up->genbuf, sizeof(up->genbuf), "%s: %q", Ebadchar, aname);
1737                                         free(s);
1738                                         error(up->genbuf);
1739                         }
1740                         name++;
1741                 }
1742         }
1743         return s;
1744 }
1745
1746 void
1747 validname(char *aname, int slashok)
1748 {
1749         validname0(aname, slashok, 0, getcallerpc(&aname));
1750 }
1751
1752 char*
1753 validnamedup(char *aname, int slashok)
1754 {
1755         return validname0(aname, slashok, 1, getcallerpc(&aname));
1756 }
1757
1758 void
1759 isdir(Chan *c)
1760 {
1761         if(c->qid.type & QTDIR)
1762                 return;
1763         error(Enotdir);
1764 }
1765
1766 /*
1767  * This is necessary because there are many
1768  * pointers to the top of a given mount list:
1769  *
1770  *      - the mhead in the namespace hash table
1771  *      - the mhead in chans returned from findmount:
1772  *        used in namec and then by unionread.
1773  *      - the mhead in chans returned from createdir:
1774  *        used in the open/create race protect, which is gone.
1775  *
1776  * The RWlock in the Mhead protects the mount list it contains.
1777  * The mount list is deleted when we cunmount.
1778  * The RWlock ensures that nothing is using the mount list at that time.
1779  *
1780  * It is okay to replace c->mh with whatever you want as
1781  * long as you are sure you have a unique reference to it.
1782  *
1783  * This comment might belong somewhere else.
1784  */
1785 void
1786 putmhead(Mhead *m)
1787 {
1788         if(m && decref(m) == 0){
1789                 m->mount = (Mount*)0xCafeBeef;
1790                 free(m);
1791         }
1792 }
1793