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71528152915301531 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- #include "u.h"
- #include "../port/lib.h"
- #include "mem.h"
- #include "dat.h"
- #include "fns.h"
- #include "../port/error.h"
- int chandebug=0; /* toggled by sysr1 */
- QLock chanprint; /* probably asking for trouble (deadlocks) -rsc */
- int domount(Chan**, Mhead**);
- void
- dumpmount(void) /* DEBUGGING */
- {
- Pgrp *pg;
- Mount *t;
- Mhead **h, **he, *f;
- if(up == nil){
- print("no process for dumpmount\n");
- return;
- }
- pg = up->pgrp;
- if(pg == nil){
- print("no pgrp for dumpmount\n");
- return;
- }
- rlock(&pg->ns);
- if(waserror()) {
- runlock(&pg->ns);
- nexterror();
- }
- he = &pg->mnthash[MNTHASH];
- for(h = pg->mnthash; h < he; h++) {
- for(f = *h; f; f = f->hash) {
- print("head: %p: %s 0x%llux.%lud %C %lud -> \n", f,
- f->from->name->s, f->from->qid.path,
- f->from->qid.vers, devtab[f->from->type]->dc,
- f->from->dev);
- for(t = f->mount; t; t = t->next)
- 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);
- }
- }
- poperror();
- runlock(&pg->ns);
- }
- char*
- channame(Chan *c) /* DEBUGGING */
- {
- if(c == nil)
- return "<nil chan>";
- if(c->name == nil)
- return "<nil name>";
- if(c->name->s == nil)
- return "<nil name.s>";
- return c->name->s;
- }
- enum
- {
- CNAMESLOP = 20
- };
- struct
- {
- Lock;
- int fid;
- Chan *free;
- Chan *list;
- }chanalloc;
- typedef struct Elemlist Elemlist;
- struct Elemlist
- {
- char *name; /* copy of name, so '/' can be overwritten */
- int nelems;
- char **elems;
- int *off;
- int mustbedir;
- };
- #define SEP(c) ((c) == 0 || (c) == '/')
- void cleancname(Cname*);
- int
- isdotdot(char *p)
- {
- return p[0]=='.' && p[1]=='.' && p[2]=='\0';
- }
- long
- incref(Ref *r)
- {
- long x;
- lock(r);
- x = ++r->ref;
- unlock(r);
- return x;
- }
- long
- decref(Ref *r)
- {
- long x;
- lock(r);
- x = --r->ref;
- unlock(r);
- if(x < 0)
- panic("deccnt pc=0x%lux", getcallerpc(&r));
- return x;
- }
- /*
- * Rather than strncpy, which zeros the rest of the buffer, kstrcpy
- * truncates if necessary, always zero terminates, does not zero fill,
- * and puts ... at the end of the string if it's too long. Usually used to
- * save a string in up->genbuf;
- */
- void
- kstrcpy(char *s, char *t, int ns)
- {
- int nt;
- nt = strlen(t);
- if(nt+1 <= ns){
- memmove(s, t, nt+1);
- return;
- }
- /* too long */
- if(ns < 4){
- /* but very short! */
- strncpy(s, t, ns);
- return;
- }
- /* truncate with ... at character boundary (very rare case) */
- memmove(s, t, ns-4);
- ns -= 4;
- s[ns] = '\0';
- /* look for first byte of UTF-8 sequence by skipping continuation bytes */
- while(ns>0 && (s[--ns]&0xC0)==0x80)
- ;
- strcpy(s+ns, "...");
- }
- int
- emptystr(char *s)
- {
- if(s == nil)
- return 1;
- if(s[0] == '\0')
- return 1;
- return 0;
- }
- /*
- * Atomically replace *p with copy of s
- */
- void
- kstrdup(char **p, char *s)
- {
- int n;
- char *t, *prev;
- static Lock l;
- n = strlen(s)+1;
- /* if it's a user, we can wait for memory; if not, something's very wrong */
- if(up){
- t = smalloc(n);
- setmalloctag(t, getcallerpc(&p));
- }else{
- t = malloc(n);
- if(t == nil)
- panic("kstrdup: no memory");
- }
- memmove(t, s, n);
- prev = *p;
- *p = t;
- free(prev);
- }
- void
- chandevreset(void)
- {
- int i;
- for(i=0; devtab[i] != nil; i++)
- devtab[i]->reset();
- }
- void
- chandevinit(void)
- {
- int i;
- for(i=0; devtab[i] != nil; i++)
- devtab[i]->init();
- }
- void
- chandevshutdown(void)
- {
- int i;
-
- /* shutdown in reverse order */
- for(i=0; devtab[i] != nil; i++)
- ;
- for(i--; i >= 0; i--)
- devtab[i]->shutdown();
- }
- Chan*
- newchan(void)
- {
- Chan *c;
- lock(&chanalloc);
- c = chanalloc.free;
- if(c != 0)
- chanalloc.free = c->next;
- unlock(&chanalloc);
- if(c == nil) {
- c = smalloc(sizeof(Chan));
- lock(&chanalloc);
- c->fid = ++chanalloc.fid;
- c->link = chanalloc.list;
- chanalloc.list = c;
- unlock(&chanalloc);
- }
- /* if you get an error before associating with a dev,
- close calls rootclose, a nop */
- c->type = 0;
- c->flag = 0;
- c->ref = 1;
- c->dev = 0;
- c->offset = 0;
- c->devoffset = 0;
- c->iounit = 0;
- c->umh = 0;
- c->uri = 0;
- c->dri = 0;
- c->aux = 0;
- c->mchan = 0;
- c->mcp = 0;
- c->mux = 0;
- memset(&c->mqid, 0, sizeof(c->mqid));
- c->name = 0;
- c->ismtpt = 0;
- return c;
- }
- static Ref ncname;
- Cname*
- newcname(char *s)
- {
- Cname *n;
- int i;
- n = smalloc(sizeof(Cname));
- i = strlen(s);
- n->len = i;
- n->alen = i+CNAMESLOP;
- n->s = smalloc(n->alen);
- memmove(n->s, s, i+1);
- n->ref = 1;
- incref(&ncname);
- return n;
- }
- void
- cnameclose(Cname *n)
- {
- if(n == nil)
- return;
- if(decref(n))
- return;
- decref(&ncname);
- free(n->s);
- free(n);
- }
- Cname*
- addelem(Cname *n, char *s)
- {
- int i, a;
- char *t;
- Cname *new;
- if(s[0]=='.' && s[1]=='\0')
- return n;
- if(n->ref > 1){
- /* copy on write */
- new = newcname(n->s);
- cnameclose(n);
- n = new;
- }
- i = strlen(s);
- if(n->len+1+i+1 > n->alen){
- a = n->len+1+i+1 + CNAMESLOP;
- t = smalloc(a);
- memmove(t, n->s, n->len+1);
- free(n->s);
- n->s = t;
- n->alen = a;
- }
- if(n->len>0 && n->s[n->len-1]!='/' && s[0]!='/') /* don't insert extra slash if one is present */
- n->s[n->len++] = '/';
- memmove(n->s+n->len, s, i+1);
- n->len += i;
- if(isdotdot(s))
- cleancname(n);
- return n;
- }
- void
- chanfree(Chan *c)
- {
- c->flag = CFREE;
- if(c->dirrock != nil){
- free(c->dirrock);
- c->dirrock = 0;
- c->nrock = 0;
- c->mrock = 0;
- }
- if(c->umh != nil){
- putmhead(c->umh);
- c->umh = nil;
- }
- if(c->umc != nil){
- cclose(c->umc);
- c->umc = nil;
- }
- if(c->mux != nil){
- muxclose(c->mux);
- c->mux = nil;
- }
- if(c->mchan != nil){
- cclose(c->mchan);
- c->mchan = nil;
- }
- cnameclose(c->name);
- lock(&chanalloc);
- c->next = chanalloc.free;
- chanalloc.free = c;
- unlock(&chanalloc);
- }
- void
- cclose(Chan *c)
- {
- if(c->flag&CFREE)
- panic("cclose %lux", getcallerpc(&c));
- if(decref(c))
- return;
- if(!waserror()){
- devtab[c->type]->close(c);
- poperror();
- }
- chanfree(c);
- }
- /*
- * Make sure we have the only copy of c. (Copy on write.)
- */
- Chan*
- cunique(Chan *c)
- {
- Chan *nc;
- if(c->ref != 1) {
- nc = cclone(c);
- cclose(c);
- c = nc;
- }
- return c;
- }
- int
- eqqid(Qid a, Qid b)
- {
- return a.path==b.path && a.vers==b.vers;
- }
- int
- eqchan(Chan *a, Chan *b, int pathonly)
- {
- if(a->qid.path != b->qid.path)
- return 0;
- if(!pathonly && a->qid.vers!=b->qid.vers)
- return 0;
- if(a->type != b->type)
- return 0;
- if(a->dev != b->dev)
- return 0;
- return 1;
- }
- int
- eqchantdqid(Chan *a, int type, int dev, Qid qid, int pathonly)
- {
- if(a->qid.path != qid.path)
- return 0;
- if(!pathonly && a->qid.vers!=qid.vers)
- return 0;
- if(a->type != type)
- return 0;
- if(a->dev != dev)
- return 0;
- return 1;
- }
- Mhead*
- newmhead(Chan *from)
- {
- Mhead *mh;
- mh = smalloc(sizeof(Mhead));
- mh->ref = 1;
- mh->from = from;
- incref(from);
- /*
- n = from->name->len;
- if(n >= sizeof(mh->fromname))
- n = sizeof(mh->fromname)-1;
- memmove(mh->fromname, from->name->s, n);
- mh->fromname[n] = 0;
- */
- return mh;
- }
- int
- cmount(Chan **newp, Chan *old, int flag, char *spec)
- {
- Pgrp *pg;
- int order, flg;
- Mhead *m, **l, *mh;
- Mount *nm, *f, *um, **h;
- Chan *new;
- if(QTDIR & (old->qid.type^(*newp)->qid.type))
- error(Emount);
- if(old->umh)print("cmount old extra umh\n");
- order = flag&MORDER;
- if((old->qid.type&QTDIR)==0 && order != MREPL)
- error(Emount);
- new = *newp;
- mh = new->umh;
- /*
- * Not allowed to bind when the old directory
- * is itself a union. (Maybe it should be allowed, but I don't see
- * what the semantics would be.)
- *
- * We need to check mh->mount->next to tell unions apart from
- * simple mount points, so that things like
- * mount -c fd /root
- * bind -c /root /
- * work. The check of mount->mflag catches things like
- * mount fd /root
- * bind -c /root /
- *
- * This is far more complicated than it should be, but I don't
- * see an easier way at the moment. -rsc
- */
- if((flag&MCREATE) && mh && mh->mount
- && (mh->mount->next || !(mh->mount->mflag&MCREATE)))
- error(Emount);
- pg = up->pgrp;
- wlock(&pg->ns);
- l = &MOUNTH(pg, old->qid);
- for(m = *l; m; m = m->hash) {
- if(eqchan(m->from, old, 1))
- break;
- l = &m->hash;
- }
- if(m == nil) {
- /*
- * nothing mounted here yet. create a mount
- * head and add to the hash table.
- */
- m = newmhead(old);
- *l = m;
- /*
- * if this is a union mount, add the old
- * node to the mount chain.
- */
- if(order != MREPL)
- m->mount = newmount(m, old, 0, 0);
- }
- wlock(&m->lock);
- if(waserror()){
- wunlock(&m->lock);
- nexterror();
- }
- wunlock(&pg->ns);
- nm = newmount(m, new, flag, spec);
- if(mh != nil && mh->mount != nil) {
- /*
- * copy a union when binding it onto a directory
- */
- flg = order;
- if(order == MREPL)
- flg = MAFTER;
- h = &nm->next;
- um = mh->mount;
- for(um = um->next; um; um = um->next) {
- f = newmount(m, um->to, flg, um->spec);
- *h = f;
- h = &f->next;
- }
- }
- if(m->mount && order == MREPL) {
- mountfree(m->mount);
- m->mount = 0;
- }
- if(flag & MCREATE)
- nm->mflag |= MCREATE;
- if(m->mount && order == MAFTER) {
- for(f = m->mount; f->next; f = f->next)
- ;
- f->next = nm;
- }
- else {
- for(f = nm; f->next; f = f->next)
- ;
- f->next = m->mount;
- m->mount = nm;
- }
- wunlock(&m->lock);
- poperror();
- return nm->mountid;
- }
- void
- cunmount(Chan *mnt, Chan *mounted)
- {
- Pgrp *pg;
- Mhead *m, **l;
- Mount *f, **p;
- if(mnt->umh) /* should not happen */
- print("cunmount newp extra umh %p has %p\n", mnt, mnt->umh);
- /*
- * It _can_ happen that mounted->umh is non-nil,
- * because mounted is the result of namec(Aopen)
- * (see sysfile.c:/^sysunmount).
- * If we open a union directory, it will have a umh.
- * Although surprising, this is okay, since the
- * cclose will take care of freeing the umh.
- */
- pg = up->pgrp;
- wlock(&pg->ns);
- l = &MOUNTH(pg, mnt->qid);
- for(m = *l; m; m = m->hash) {
- if(eqchan(m->from, mnt, 1))
- break;
- l = &m->hash;
- }
- if(m == 0) {
- wunlock(&pg->ns);
- error(Eunmount);
- }
- wlock(&m->lock);
- if(mounted == 0) {
- *l = m->hash;
- wunlock(&pg->ns);
- mountfree(m->mount);
- m->mount = nil;
- cclose(m->from);
- wunlock(&m->lock);
- putmhead(m);
- return;
- }
- p = &m->mount;
- for(f = *p; f; f = f->next) {
- /* BUG: Needs to be 2 pass */
- if(eqchan(f->to, mounted, 1) ||
- (f->to->mchan && eqchan(f->to->mchan, mounted, 1))) {
- *p = f->next;
- f->next = 0;
- mountfree(f);
- if(m->mount == nil) {
- *l = m->hash;
- cclose(m->from);
- wunlock(&m->lock);
- wunlock(&pg->ns);
- putmhead(m);
- return;
- }
- wunlock(&m->lock);
- wunlock(&pg->ns);
- return;
- }
- p = &f->next;
- }
- wunlock(&m->lock);
- wunlock(&pg->ns);
- error(Eunion);
- }
- Chan*
- cclone(Chan *c)
- {
- Chan *nc;
- Walkqid *wq;
- wq = devtab[c->type]->walk(c, nil, nil, 0);
- if(wq == nil)
- error("clone failed");
- nc = wq->clone;
- free(wq);
- nc->name = c->name;
- if(c->name)
- incref(c->name);
- return nc;
- }
- int
- findmount(Chan **cp, Mhead **mp, int type, int dev, Qid qid)
- {
- Pgrp *pg;
- Mhead *m;
- pg = up->pgrp;
- rlock(&pg->ns);
- for(m = MOUNTH(pg, qid); m; m = m->hash){
- rlock(&m->lock);
- if(m->from == nil){
- print("m %p m->from 0\n", m);
- runlock(&m->lock);
- continue;
- }
- if(eqchantdqid(m->from, type, dev, qid, 1)){
- runlock(&pg->ns);
- if(mp != nil){
- incref(m);
- if(*mp != nil)
- putmhead(*mp);
- *mp = m;
- }
- if(*cp != nil)
- cclose(*cp);
- incref(m->mount->to);
- *cp = m->mount->to;
- runlock(&m->lock);
- return 1;
- }
- runlock(&m->lock);
- }
- runlock(&pg->ns);
- return 0;
- }
- int
- domount(Chan **cp, Mhead **mp)
- {
- return findmount(cp, mp, (*cp)->type, (*cp)->dev, (*cp)->qid);
- }
- Chan*
- undomount(Chan *c, Cname *name)
- {
- Chan *nc;
- Pgrp *pg;
- Mount *t;
- Mhead **h, **he, *f;
- pg = up->pgrp;
- rlock(&pg->ns);
- if(waserror()) {
- runlock(&pg->ns);
- nexterror();
- }
- he = &pg->mnthash[MNTHASH];
- for(h = pg->mnthash; h < he; h++) {
- for(f = *h; f; f = f->hash) {
- if(strcmp(f->from->name->s, name->s) != 0)
- continue;
- for(t = f->mount; t; t = t->next) {
- if(eqchan(c, t->to, 1)) {
- /*
- * We want to come out on the left hand side of the mount
- * point using the element of the union that we entered on.
- * To do this, find the element that has a from name of
- * c->name->s.
- */
- if(strcmp(t->head->from->name->s, name->s) != 0)
- continue;
- nc = t->head->from;
- incref(nc);
- cclose(c);
- c = nc;
- break;
- }
- }
- }
- }
- poperror();
- runlock(&pg->ns);
- return c;
- }
- /*
- * Either walks all the way or not at all. No partial results in *cp.
- * *nerror is the number of names to display in an error message.
- */
- static char Edoesnotexist[] = "does not exist";
- int
- walk(Chan **cp, char **names, int nnames, int nomount, int *nerror)
- {
- int dev, dotdot, i, n, nhave, ntry, type;
- Chan *c, *nc;
- Cname *cname;
- Mount *f;
- Mhead *mh, *nmh;
- Walkqid *wq;
- c = *cp;
- incref(c);
- cname = c->name;
- incref(cname);
- mh = nil;
- /*
- * While we haven't gotten all the way down the path:
- * 1. step through a mount point, if any
- * 2. send a walk request for initial dotdot or initial prefix without dotdot
- * 3. move to the first mountpoint along the way.
- * 4. repeat.
- *
- * An invariant is that each time through the loop, c is on the undomount
- * side of the mount point, and c's name is cname.
- */
- for(nhave=0; nhave<nnames; nhave+=n){
- if((c->qid.type&QTDIR)==0){
- if(nerror)
- *nerror = nhave;
- cnameclose(cname);
- cclose(c);
- strcpy(up->errstr, Enotdir);
- if(mh != nil)
- putmhead(mh);
- return -1;
- }
- ntry = nnames - nhave;
- if(ntry > MAXWELEM)
- ntry = MAXWELEM;
- dotdot = 0;
- for(i=0; i<ntry; i++){
- if(isdotdot(names[nhave+i])){
- if(i==0) {
- dotdot = 1;
- ntry = 1;
- } else
- ntry = i;
- break;
- }
- }
- if(!dotdot && !nomount)
- domount(&c, &mh);
- type = c->type;
- dev = c->dev;
- if((wq = devtab[type]->walk(c, nil, names+nhave, ntry)) == nil){
- /* try a union mount, if any */
- if(mh && !nomount){
- /*
- * mh->mount->to == c, so start at mh->mount->next
- */
- rlock(&mh->lock);
- for(f = mh->mount->next; f; f = f->next)
- if((wq = devtab[f->to->type]->walk(f->to, nil, names+nhave, ntry)) != nil)
- break;
- runlock(&mh->lock);
- if(f != nil){
- type = f->to->type;
- dev = f->to->dev;
- }
- }
- if(wq == nil){
- cclose(c);
- cnameclose(cname);
- if(nerror)
- *nerror = nhave+1;
- if(mh != nil)
- putmhead(mh);
- return -1;
- }
- }
- nmh = nil;
- if(dotdot){
- assert(wq->nqid == 1);
- assert(wq->clone != nil);
- cname = addelem(cname, "..");
- nc = undomount(wq->clone, cname);
- n = 1;
- }else{
- nc = nil;
- if(!nomount)
- for(i=0; i<wq->nqid && i<ntry-1; i++)
- if(findmount(&nc, &nmh, type, dev, wq->qid[i]))
- break;
- if(nc == nil){ /* no mount points along path */
- if(wq->clone == nil){
- cclose(c);
- cnameclose(cname);
- if(wq->nqid==0 || (wq->qid[wq->nqid-1].type&QTDIR)){
- if(nerror)
- *nerror = nhave+wq->nqid+1;
- strcpy(up->errstr, Edoesnotexist);
- }else{
- if(nerror)
- *nerror = nhave+wq->nqid;
- strcpy(up->errstr, Enotdir);
- }
- free(wq);
- if(mh != nil)
- putmhead(mh);
- return -1;
- }
- n = wq->nqid;
- nc = wq->clone;
- }else{ /* stopped early, at a mount point */
- if(wq->clone != nil){
- cclose(wq->clone);
- wq->clone = nil;
- }
- n = i+1;
- }
- for(i=0; i<n; i++)
- cname = addelem(cname, names[nhave+i]);
- }
- cclose(c);
- c = nc;
- putmhead(mh);
- mh = nmh;
- free(wq);
- }
- putmhead(mh);
- c = cunique(c);
- if(c->umh != nil){ //BUG
- print("walk umh\n");
- putmhead(c->umh);
- c->umh = nil;
- }
- cnameclose(c->name);
- c->name = cname;
- cclose(*cp);
- *cp = c;
- if(nerror)
- *nerror = 0;
- return 0;
- }
- /*
- * c is a mounted non-creatable directory. find a creatable one.
- */
- Chan*
- createdir(Chan *c, Mhead *m)
- {
- Chan *nc;
- Mount *f;
- rlock(&m->lock);
- if(waserror()) {
- runlock(&m->lock);
- nexterror();
- }
- for(f = m->mount; f; f = f->next) {
- if(f->mflag&MCREATE) {
- nc = cclone(f->to);
- runlock(&m->lock);
- poperror();
- cclose(c);
- return nc;
- }
- }
- error(Enocreate);
- return 0;
- }
- void
- saveregisters(void)
- {
- }
- /*
- * In place, rewrite name to compress multiple /, eliminate ., and process ..
- */
- void
- cleancname(Cname *n)
- {
- char *p;
- if(n->s[0] == '#'){
- p = strchr(n->s, '/');
- if(p == nil)
- return;
- cleanname(p);
- /*
- * The correct name is #i rather than #i/,
- * but the correct name of #/ is #/.
- */
- if(strcmp(p, "/")==0 && n->s[1] != '/')
- *p = '\0';
- }else
- cleanname(n->s);
- n->len = strlen(n->s);
- }
- static void
- growparse(Elemlist *e)
- {
- char **new;
- int *inew;
- enum { Delta = 8 };
- if(e->nelems % Delta == 0){
- new = smalloc((e->nelems+Delta) * sizeof(char*));
- memmove(new, e->elems, e->nelems*sizeof(char*));
- free(e->elems);
- e->elems = new;
- inew = smalloc((e->nelems+Delta+1) * sizeof(int));
- memmove(inew, e->off, e->nelems*sizeof(int));
- free(e->off);
- e->off = inew;
- }
- }
- /*
- * The name is known to be valid.
- * Copy the name so slashes can be overwritten.
- * An empty string will set nelem=0.
- * A path ending in / or /. or /.//./ etc. will have
- * e.mustbedir = 1, so that we correctly
- * reject, e.g., "/adm/users/." when /adm/users is a file
- * rather than a directory.
- */
- static void
- parsename(char *name, Elemlist *e)
- {
- char *slash;
- kstrdup(&e->name, name);
- name = e->name;
- e->nelems = 0;
- e->elems = nil;
- e->off = smalloc(sizeof(int));
- e->off[0] = skipslash(name) - name;
- for(;;){
- name = skipslash(name);
- if(*name=='\0'){
- e->mustbedir = 1;
- break;
- }
- growparse(e);
- e->elems[e->nelems++] = name;
- slash = utfrune(name, '/');
- if(slash == nil){
- e->off[e->nelems] = name+strlen(name) - e->name;
- e->mustbedir = 0;
- break;
- }
- e->off[e->nelems] = slash - e->name;
- *slash++ = '\0';
- name = slash;
- }
- }
- void*
- memrchr(void *va, int c, long n)
- {
- uchar *a, *e;
- a = va;
- for(e=a+n-1; e>a; e--)
- if(*e == c)
- return e;
- return nil;
- }
- void
- nameerror(char *name, char *error)
- {
- int len;
- char tmperr[ERRMAX], *p;
- strcpy(tmperr, error); /* error might be in genbuf or tmperr */
- len = strlen(name);
- if(len < ERRMAX/3 || (p=strrchr(name, '/'))==nil || p==name)
- snprint(up->genbuf, sizeof up->genbuf, "%s", name);
- else
- snprint(up->genbuf, sizeof up->genbuf, "...%s", p);
- snprint(up->errstr, ERRMAX, "%#q %s", up->genbuf, tmperr);
- nexterror();
- }
- /*
- * Turn a name into a channel.
- * &name[0] is known to be a valid address. It may be a kernel address.
- *
- * Opening with amode Aopen, Acreate, Aremove, or Aaccess guarantees
- * that the result will be the only reference to that particular fid.
- * This is necessary since we might pass the result to
- * devtab[]->remove().
- *
- * Opening Atodir or Amount does not guarantee this.
- *
- * Under certain circumstances, opening Aaccess will cause
- * an unnecessary clone in order to get a cunique Chan so it
- * can attach the correct name. Sysstat and sys_stat need the
- * correct name so they can rewrite the stat info.
- */
- Chan*
- namec(char *aname, int amode, int omode, ulong perm)
- {
- int n, t, nomount, npath;
- Chan *c, *cnew;
- Cname *cname;
- Elemlist e;
- Rune r;
- Mhead *m;
- char *createerr, tmperrbuf[ERRMAX];
- char *name;
- name = aname;
- if(name[0] == '\0')
- error("empty file name");
- name = validnamedup(name, 1);
- if(waserror()){
- free(name);
- nexterror();
- }
- /*
- * Find the starting off point (the current slash, the root of
- * a device tree, or the current dot) as well as the name to
- * evaluate starting there.
- */
- nomount = 0;
- switch(name[0]){
- case '/':
- c = up->slash;
- incref(c);
- break;
-
- case '#':
- nomount = 1;
- up->genbuf[0] = '\0';
- n = 0;
- while(*name!='\0' && (*name != '/' || n < 2)){
- if(n >= sizeof(up->genbuf)-1)
- error(Efilename);
- up->genbuf[n++] = *name++;
- }
- up->genbuf[n] = '\0';
- /*
- * noattach is sandboxing.
- *
- * the OK exceptions are:
- * | it only gives access to pipes you create
- * d this process's file descriptors
- * e this process's environment
- * the iffy exceptions are:
- * c time and pid, but also cons and consctl
- * p control of your own processes (and unfortunately
- * any others left unprotected)
- */
- n = chartorune(&r, up->genbuf+1)+1;
- /* actually / is caught by parsing earlier */
- if(utfrune("M", r))
- error(Enoattach);
- if(up->pgrp->noattach && utfrune("|decp", r)==nil)
- error(Enoattach);
- t = devno(r, 1);
- if(t == -1)
- error(Ebadsharp);
- c = devtab[t]->attach(up->genbuf+n);
- break;
- default:
- c = up->dot;
- incref(c);
- break;
- }
- e.name = nil;
- e.elems = nil;
- e.off = nil;
- e.nelems = 0;
- if(waserror()){
- cclose(c);
- free(e.name);
- free(e.elems);
- free(e.off);
- //dumpmount();
- nexterror();
- }
- /*
- * Build a list of elements in the path.
- */
- parsename(name, &e);
- /*
- * On create, ....
- */
- if(amode == Acreate){
- /* perm must have DMDIR if last element is / or /. */
- if(e.mustbedir && !(perm&DMDIR)){
- npath = e.nelems;
- nameerror(aname, "create without DMDIR");
- }
- /* don't try to walk the last path element just yet. */
- if(e.nelems == 0)
- error(Eexist);
- e.nelems--;
- }
- if(walk(&c, e.elems, e.nelems, nomount, &npath) < 0){
- if(npath < 0 || npath > e.nelems){
- print("namec %s walk error npath=%d\n", aname, npath);
- nexterror();
- }
- nameerror(aname, up->errstr);
- }
- if(e.mustbedir && !(c->qid.type&QTDIR)){
- npath = e.nelems;
- nameerror(aname, "not a directory");
- }
- if(amode == Aopen && (omode&3) == OEXEC && (c->qid.type&QTDIR)){
- npath = e.nelems;
- error("cannot exec directory");
- }
- switch(amode){
- case Abind:
- m = nil;
- if(!nomount)
- domount(&c, &m);
- if(c->umh != nil)
- putmhead(c->umh);
- c->umh = m;
- break;
- case Aaccess:
- case Aremove:
- case Aopen:
- Open:
- /* save the name; domount might change c */
- cname = c->name;
- incref(cname);
- m = nil;
- if(!nomount)
- domount(&c, &m);
- /* our own copy to open or remove */
- c = cunique(c);
- /* now it's our copy anyway, we can put the name back */
- cnameclose(c->name);
- c->name = cname;
- /* record whether c is on a mount point */
- c->ismtpt = m!=nil;
- switch(amode){
- case Aaccess:
- case Aremove:
- putmhead(m);
- break;
- case Aopen:
- case Acreate:
- if(c->umh != nil){
- print("cunique umh Open\n");
- putmhead(c->umh);
- c->umh = nil;
- }
- /* only save the mount head if it's a multiple element union */
- if(m && m->mount && m->mount->next)
- c->umh = m;
- else
- putmhead(m);
- /* save registers else error() in open has wrong value of c saved */
- saveregisters();
- if(omode == OEXEC)
- c->flag &= ~CCACHE;
- c = devtab[c->type]->open(c, omode&~OCEXEC);
- if(omode & OCEXEC)
- c->flag |= CCEXEC;
- if(omode & ORCLOSE)
- c->flag |= CRCLOSE;
- break;
- }
- break;
- case Atodir:
- /*
- * Directories (e.g. for cd) are left before the mount point,
- * so one may mount on / or . and see the effect.
- */
- if(!(c->qid.type & QTDIR))
- error(Enotdir);
- break;
- case Amount:
- /*
- * When mounting on an already mounted upon directory,
- * one wants subsequent mounts to be attached to the
- * original directory, not the replacement. Don't domount.
- */
- break;
- case Acreate:
- /*
- * We've already walked all but the last element.
- * If the last exists, try to open it OTRUNC.
- * If omode&OEXCL is set, just give up.
- */
- e.nelems++;
- if(walk(&c, e.elems+e.nelems-1, 1, nomount, nil) == 0){
- if(omode&OEXCL)
- error(Eexist);
- omode |= OTRUNC;
- goto Open;
- }
- /*
- * The semantics of the create(2) system call are that if the
- * file exists and can be written, it is to be opened with truncation.
- * On the other hand, the create(5) message fails if the file exists.
- * If we get two create(2) calls happening simultaneously,
- * they might both get here and send create(5) messages, but only
- * one of the messages will succeed. To provide the expected create(2)
- * semantics, the call with the failed message needs to try the above
- * walk again, opening for truncation. This correctly solves the
- * create/create race, in the sense that any observable outcome can
- * be explained as one happening before the other.
- * The create/create race is quite common. For example, it happens
- * when two rc subshells simultaneously update the same
- * environment variable.
- *
- * The implementation still admits a create/create/remove race:
- * (A) walk to file, fails
- * (B) walk to file, fails
- * (A) create file, succeeds, returns
- * (B) create file, fails
- * (A) remove file, succeeds, returns
- * (B) walk to file, return failure.
- *
- * This is hardly as common as the create/create race, and is really
- * not too much worse than what might happen if (B) got a hold of a
- * file descriptor and then the file was removed -- either way (B) can't do
- * anything with the result of the create call. So we don't care about this race.
- *
- * Applications that care about more fine-grained decision of the races
- * can use the OEXCL flag to get at the underlying create(5) semantics;
- * by default we provide the common case.
- *
- * We need to stay behind the mount point in case we
- * need to do the first walk again (should the create fail).
- *
- * We also need to cross the mount point and find the directory
- * in the union in which we should be creating.
- *
- * The channel staying behind is c, the one moving forward is cnew.
- */
- m = nil;
- cnew = nil; /* is this assignment necessary? */
- if(!waserror()){ /* try create */
- if(!nomount && findmount(&cnew, &m, c->type, c->dev, c->qid))
- cnew = createdir(cnew, m);
- else{
- cnew = c;
- incref(cnew);
- }
- /*
- * We need our own copy of the Chan because we're
- * about to send a create, which will move it. Once we have
- * our own copy, we can fix the name, which might be wrong
- * if findmount gave us a new Chan.
- */
- cnew = cunique(cnew);
- cnameclose(cnew->name);
- cnew->name = c->name;
- incref(cnew->name);
- devtab[cnew->type]->create(cnew, e.elems[e.nelems-1], omode&~(OEXCL|OCEXEC), perm);
- poperror();
- if(omode & OCEXEC)
- cnew->flag |= CCEXEC;
- if(omode & ORCLOSE)
- cnew->flag |= CRCLOSE;
- if(m)
- putmhead(m);
- cclose(c);
- c = cnew;
- c->name = addelem(c->name, e.elems[e.nelems-1]);
- break;
- }else{ /* create failed */
- cclose(cnew);
- if(m)
- putmhead(m);
- if(omode & OEXCL)
- nexterror();
- /* save error */
- createerr = up->errstr;
- up->errstr = tmperrbuf;
- /* note: we depend that walk does not error */
- if(walk(&c, e.elems+e.nelems-1, 1, nomount, nil) < 0){
- up->errstr = createerr;
- error(createerr); /* report true error */
- }
- up->errstr = createerr;
- omode |= OTRUNC;
- goto Open;
- }
- panic("namec: not reached");
- default:
- panic("unknown namec access %d\n", amode);
- }
- /* place final element in genbuf for e.g. exec */
- if(e.nelems > 0)
- kstrcpy(up->genbuf, e.elems[e.nelems-1], sizeof up->genbuf);
- else
- kstrcpy(up->genbuf, ".", sizeof up->genbuf);
- free(e.name);
- free(e.elems);
- free(e.off);
- poperror(); /* e c */
- free(name);
- poperror(); /* name */
- return c;
- }
- /*
- * name is valid. skip leading / and ./ as much as possible
- */
- char*
- skipslash(char *name)
- {
- while(name[0]=='/' || (name[0]=='.' && (name[1]==0 || name[1]=='/')))
- name++;
- return name;
- }
- char isfrog[256]={
- /*NUL*/ 1, 1, 1, 1, 1, 1, 1, 1,
- /*BKS*/ 1, 1, 1, 1, 1, 1, 1, 1,
- /*DLE*/ 1, 1, 1, 1, 1, 1, 1, 1,
- /*CAN*/ 1, 1, 1, 1, 1, 1, 1, 1,
- ['/'] 1,
- [0x7f] 1,
- };
- /*
- * Check that the name
- * a) is in valid memory.
- * b) is shorter than 2^16 bytes, so it can fit in a 9P string field.
- * c) contains no frogs.
- * The first byte is known to be addressible by the requester, so the
- * routine works for kernel and user memory both.
- * The parameter slashok flags whether a slash character is an error
- * or a valid character.
- *
- * The parameter dup flags whether the string should be copied
- * out of user space before being scanned the second time.
- * (Otherwise a malicious thread could remove the NUL, causing us
- * to access unchecked addresses.)
- */
- static char*
- validname0(char *aname, int slashok, int dup, ulong pc)
- {
- char *p, *ename, *name, *s;
- uint t;
- int c, n;
- Rune r;
- name = aname;
- if(((ulong)name & KZERO) != KZERO) {
- if(!dup)
- print("warning: validname called from %lux with user pointer", pc);
- p = name;
- t = BY2PG-((ulong)p&(BY2PG-1));
- while((ename=vmemchr(p, 0, t)) == nil) {
- p += t;
- t = BY2PG;
- }
- }else
- ename = memchr(name, 0, (1<<16));
- if(ename==nil || ename-name>=(1<<16))
- error("name too long");
- s = nil;
- if(dup){
- n = ename-name;
- s = smalloc(n+1);
- memmove(s, name, n);
- s[n] = 0;
- aname = s;
- name = s;
- }
-
- while(*name){
- /* all characters above '~' are ok */
- c = *(uchar*)name;
- if(c >= Runeself)
- name += chartorune(&r, name);
- else{
- if(isfrog[c])
- if(!slashok || c!='/'){
- snprint(up->genbuf, sizeof(up->genbuf), "%s: %q", Ebadchar, aname);
- free(s);
- error(up->genbuf);
- }
- name++;
- }
- }
- return s;
- }
- void
- validname(char *aname, int slashok)
- {
- validname0(aname, slashok, 0, getcallerpc(&aname));
- }
- char*
- validnamedup(char *aname, int slashok)
- {
- return validname0(aname, slashok, 1, 0);
- }
- void
- isdir(Chan *c)
- {
- if(c->qid.type & QTDIR)
- return;
- error(Enotdir);
- }
- /*
- * This is necessary because there are many
- * pointers to the top of a given mount list:
- *
- * - the mhead in the namespace hash table
- * - the mhead in chans returned from findmount:
- * used in namec and then by unionread.
- * - the mhead in chans returned from createdir:
- * used in the open/create race protect, which is gone.
- *
- * The RWlock in the Mhead protects the mount list it contains.
- * The mount list is deleted when we cunmount.
- * The RWlock ensures that nothing is using the mount list at that time.
- *
- * It is okay to replace c->mh with whatever you want as
- * long as you are sure you have a unique reference to it.
- *
- * This comment might belong somewhere else.
- */
- void
- putmhead(Mhead *m)
- {
- if(m && decref(m) == 0){
- m->mount = (Mount*)0xCafeBeef;
- free(m);
- }
- }
|