ref: eec4e10419d1fa8955c30bacb4b49b8fdb426f78
dir: /kern/chan.c/
#include "u.h"
#include "lib.h"
#include "dat.h"
#include "fns.h"
#include "error.h"
enum
{
PATHSLOP = 20,
PATHMSLOP = 20,
};
static struct Chanalloc
{
Lock lk;
int fid;
Chan *free;
Chan *list;
}chanalloc;
typedef struct Elemlist Elemlist;
struct Elemlist
{
char *aname; /* original name */
char *name; /* copy of name, so '/' can be overwritten */
int nelems;
char **elems;
int *off;
int mustbedir;
int nerror;
int prefix;
};
char*
chanpath(Chan *c)
{
if(c == nil)
return "<nil chan>";
if(c->path == nil)
return "<nil path>";
if(c->path->s == nil)
return "<nil path.s>";
return c->path->s;
}
int
isdotdot(char *p)
{
return p[0]=='.' && p[1]=='.' && p[2]=='\0';
}
int
incref(Ref *r)
{
int x;
lock(&r->lk);
x = ++r->ref;
unlock(&r->lk);
return x;
}
int
decref(Ref *r)
{
int x;
lock(&r->lk);
x = --r->ref;
unlock(&r->lk);
if(x < 0)
panic("decref, pc=0x%p", 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 < ns){
memmove(s, t, nt);
s[nt] = '\0';
return;
}
/* too long, truncate */
nt = ns-1;
memmove(s, t, nt);
s[nt] = '\0';
/* append ... if there is space */
ns -= 4;
if(ns < 0)
return;
/* 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;
n = strlen(s);
/* if it's a user, we can wait for memory; if not, something's very wrong */
if(up != nil)
t = smalloc(n+1);
else{
t = malloc(n+1);
if(t == nil)
panic("kstrdup: no memory");
}
setmalloctag(t, getcallerpc(&p));
memmove(t, s, n);
t[n] = '\0';
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.lk);
c = chanalloc.free;
if(c != nil){
chanalloc.free = c->next;
c->next = nil;
} else {
unlock(&chanalloc.lk);
c = smalloc(sizeof(Chan));
lock(&chanalloc.lk);
c->link = chanalloc.list;
chanalloc.list = c;
}
if(c->fid == 0)
c->fid = ++chanalloc.fid;
unlock(&chanalloc.lk);
/* if you get an error before associating with a dev,
close calls rootclose, a nop */
c->type = 0;
c->flag = 0;
c->ref.ref = 1;
c->dev = 0;
c->offset = 0;
c->devoffset = 0;
c->iounit = 0;
c->umh = nil;
c->umc = nil;
c->uri = 0;
c->dri = 0;
c->dirrock = nil;
c->nrock = 0;
c->mrock = 0;
c->ismtpt = 0;
c->mux = nil;
c->aux = nil;
c->mchan = nil;
memset(&c->mqid, 0, sizeof(c->mqid));
c->path = nil;
return c;
}
Path*
newpath(char *s)
{
int i;
Path *p;
p = smalloc(sizeof(Path));
i = strlen(s);
p->len = i;
p->alen = i+PATHSLOP;
p->s = smalloc(p->alen);
memmove(p->s, s, i+1);
p->ref.ref = 1;
/*
* Cannot use newpath for arbitrary names because the mtpt
* array will not be populated correctly. The names #/ and / are
* allowed, but other names with / in them draw warnings.
*/
if(strchr(s, '/') != nil && strcmp(s, "#/") != 0 && strcmp(s, "/") != 0)
print("newpath: %s from %#p\n", s, getcallerpc(&s));
p->mlen = 1;
p->malen = PATHMSLOP;
p->mtpt = smalloc(p->malen*sizeof p->mtpt[0]);
return p;
}
static Path*
copypath(Path *p)
{
int i;
Path *pp;
pp = smalloc(sizeof(Path));
pp->ref.ref = 1;
pp->len = p->len;
pp->alen = p->alen;
pp->s = smalloc(p->alen);
memmove(pp->s, p->s, p->len+1);
pp->mlen = p->mlen;
pp->malen = p->malen;
pp->mtpt = smalloc(p->malen*sizeof pp->mtpt[0]);
for(i=0; i<pp->mlen; i++){
pp->mtpt[i] = p->mtpt[i];
if(pp->mtpt[i] != nil)
incref(&pp->mtpt[i]->ref);
}
return pp;
}
void
pathclose(Path *p)
{
int i;
if(p == nil || decref(&p->ref))
return;
for(i=0; i<p->mlen; i++)
if(p->mtpt[i] != nil)
cclose(p->mtpt[i]);
free(p->mtpt);
free(p->s);
free(p);
}
/*
* In place, rewrite name to compress multiple /, eliminate ., and process ..
* (Really only called to remove a trailing .. that has been added.
* Otherwise would need to update n->mtpt as well.)
*/
static void
fixdotdotname(Path *p)
{
char *r;
if(p->s[0] == '#'){
r = strchr(p->s, '/');
if(r == nil)
return;
cleanname(r);
/*
* The correct name is #i rather than #i/,
* but the correct name of #/ is #/.
*/
if(strcmp(r, "/")==0 && p->s[1] != '/')
*r = '\0';
}else
cleanname(p->s);
p->len = strlen(p->s);
}
static Path*
uniquepath(Path *p)
{
Path *new;
if(p->ref.ref > 1){
/* copy on write */
new = copypath(p);
pathclose(p);
p = new;
}
return p;
}
static Path*
addelem(Path *p, char *s, Chan *from)
{
char *t;
int a, i;
Chan *c, **tt;
if(s[0]=='.' && s[1]=='\0')
return p;
p = uniquepath(p);
i = strlen(s);
a = p->len+1+i+1;
if(a > p->alen){
a += PATHSLOP;
t = smalloc(a);
memmove(t, p->s, p->len+1);
free(p->s);
p->s = t;
p->alen = a;
}
/* don't insert extra slash if one is present */
if(p->len>0 && p->s[p->len-1]!='/' && s[0]!='/')
p->s[p->len++] = '/';
memmove(p->s+p->len, s, i+1);
p->len += i;
if(isdotdot(s)){
fixdotdotname(p);
if(p->mlen > 1 && (c = p->mtpt[--p->mlen]) != nil){
p->mtpt[p->mlen] = nil;
cclose(c);
}
}else{
if(p->mlen >= p->malen){
p->malen = p->mlen+1+PATHMSLOP;
tt = smalloc(p->malen*sizeof tt[0]);
memmove(tt, p->mtpt, p->mlen*sizeof tt[0]);
free(p->mtpt);
p->mtpt = tt;
}
p->mtpt[p->mlen++] = from;
if(from != nil)
incref(&from->ref);
}
return p;
}
void
chanfree(Chan *c)
{
c->flag = CFREE;
if(c->dirrock != nil){
free(c->dirrock);
c->dirrock = nil;
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;
}
pathclose(c->path);
c->path = nil;
lock(&chanalloc.lk);
c->next = chanalloc.free;
chanalloc.free = c;
unlock(&chanalloc.lk);
}
void
cclose(Chan *c)
{
if(c == nil || c->ref.ref < 1 || c->flag&CFREE)
panic("cclose %#p", getcallerpc(&c));
if(decref(&c->ref))
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.ref != 1){
nc = cclone(c);
cclose(c);
c = nc;
}
if(c->umh != nil){ //BUG
print("cunique umh != nil from %#p\n", getcallerpc(&c));
putmhead(c->umh);
c->umh = nil;
}
return c;
}
int
eqqid(Qid a, Qid b)
{
return a.path==b.path && a.vers==b.vers;
}
int
eqchan(Chan *a, Chan *b, int skipvers)
{
if(a->qid.path != b->qid.path)
return 0;
if(!skipvers && 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 skipvers)
{
if(a->qid.path != qid.path)
return 0;
if(!skipvers && a->qid.vers!=qid.vers)
return 0;
if(a->type != type)
return 0;
if(a->dev != dev)
return 0;
return 1;
}
Mhead*
newmhead(Chan *from)
{
Mhead *mh;
mh = smalloc(sizeof(Mhead));
mh->ref.ref = 1;
mh->from = from;
incref(&from->ref);
return mh;
}
/*
* 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 in cunmount() and closepgrp().
* 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 == nil)
return;
if(decref(&m->ref))
return;
assert(m->mount == nil);
cclose(m->from);
free(m);
}
int
cmount(Chan *new, Chan *old, int flag, char *spec)
{
int order;
Mhead *m, **l, *mh;
Mount *nm, *f, *um;
Pgrp *pg;
if(old->umh != nil)
print("cmount: unexpected umh, caller %#p\n", getcallerpc(&new));
if(QTDIR & (old->qid.type^new->qid.type))
error(Emount);
order = flag&MORDER;
if((old->qid.type&QTDIR) == 0 && order != MREPL)
error(Emount);
nm = newmount(new, flag, spec);
mh = new->umh;
if(mh != nil) {
rlock(&mh->lock);
if(waserror()) {
runlock(&mh->lock);
mountfree(nm);
nexterror();
}
um = mh->mount;
if(um != nil){
/*
* Not allowed to bind when the old directory is itself a union.
* (Maybe it should be allowed, but I don't see what the semantics
* would be.)
*
* We need to check mh->mount->next to tell unions apart from
* simple mount points, so that things like
* mount -c fd /root
* bind -c /root /
* work.
*
* The check of mount->mflag allows things like
* mount fd /root
* bind -c /root /
*
* This is far more complicated than it should be, but I don't
* see an easier way at the moment.
*/
if((flag&MCREATE) != 0 && (um->next != nil || (um->mflag&MCREATE) == 0))
error(Emount);
/*
* copy a union when binding it onto a directory
*/
f = nm;
for(um = um->next; um != nil; um = um->next){
f->next = newmount(um->to, order==MREPL? MAFTER: order, um->spec);
f = f->next;
}
}
runlock(&mh->lock);
poperror();
}
pg = up->pgrp;
wlock(&pg->ns);
l = &MOUNTH(pg, old->qid);
for(m = *l; m != nil; 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);
/*
* if this is a union mount, add the old
* node to the mount chain.
*/
if(order != MREPL)
m->mount = newmount(old, 0, nil);
*l = m;
}
wlock(&m->lock);
um = m->mount;
if(um != nil && order == MAFTER){
for(f = um; f->next != nil; f = f->next)
;
f->next = nm;
um = nil;
} else {
if(order != MREPL){
for(f = nm; f->next != nil; f = f->next)
;
f->next = um;
um = nil;
}
m->mount = nm;
}
order = nm->mountid;
wunlock(&m->lock);
wunlock(&pg->ns);
mountfree(um);
return order;
}
void
cunmount(Chan *mnt, Chan *mounted)
{
Pgrp *pg;
Mhead *m, **l;
Mount *f, **p;
if(mnt->umh != nil) /* 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 != nil; m = m->hash){
if(eqchan(m->from, mnt, 1))
break;
l = &m->hash;
}
if(m == nil){
wunlock(&pg->ns);
error(Eunmount);
}
wlock(&m->lock);
f = m->mount;
if(mounted == nil){
*l = m->hash;
m->mount = nil;
wunlock(&m->lock);
wunlock(&pg->ns);
mountfree(f);
putmhead(m);
return;
}
for(p = &m->mount; f != nil; f = f->next){
if(eqchan(f->to, mounted, 1) ||
(f->to->mchan != nil && eqchan(f->to->mchan, mounted, 1))){
*p = f->next;
f->next = nil;
if(m->mount == nil){
*l = m->hash;
wunlock(&m->lock);
wunlock(&pg->ns);
mountfree(f);
putmhead(m);
return;
}
wunlock(&m->lock);
wunlock(&pg->ns);
mountfree(f);
return;
}
p = &f->next;
}
wunlock(&m->lock);
wunlock(&pg->ns);
error(Eunion);
}
Chan*
cclone(Chan *c)
{
Chan *nc;
Walkqid *wq;
if(c == nil || c->ref.ref < 1 || c->flag&CFREE)
panic("cclone: %#p", getcallerpc(&c));
wq = devtab[c->type]->walk(c, nil, nil, 0);
if(wq == nil)
error("clone failed");
nc = wq->clone;
free(wq);
if((nc->path = c->path) != nil)
incref(&c->path->ref);
return nc;
}
/* also used by sysfile.c:/^mountfix */
int
findmount(Chan **cp, Mhead **mp, int type, int dev, Qid qid)
{
Chan *to;
Pgrp *pg;
Mhead *m;
pg = up->pgrp;
rlock(&pg->ns);
for(m = MOUNTH(pg, qid); m != nil; m = m->hash){
if(eqchantdqid(m->from, type, dev, qid, 1)){
if(mp != nil)
incref(&m->ref);
rlock(&m->lock);
to = m->mount->to;
incref(&to->ref);
runlock(&m->lock);
runlock(&pg->ns);
if(mp != nil){
putmhead(*mp);
*mp = m;
}
if(*cp != nil)
cclose(*cp);
*cp = to;
return 1;
}
}
runlock(&pg->ns);
return 0;
}
/*
* Calls findmount but also updates path.
*/
static int
domount(Chan **cp, Mhead **mp, Path **path)
{
Chan **lc, *from;
Path *p;
if(findmount(cp, mp, (*cp)->type, (*cp)->dev, (*cp)->qid) == 0)
return 0;
if(path != nil){
p = *path;
p = uniquepath(p);
if(p->mlen <= 0)
print("domount: path %s has mlen==%d\n", p->s, p->mlen);
else{
from = (*mp)->from;
incref(&from->ref);
lc = &p->mtpt[p->mlen-1];
if(*lc != nil)
cclose(*lc);
*lc = from;
}
*path = p;
}
return 1;
}
/*
* If c is the right-hand-side of a mount point, returns the left hand side.
* Changes name to reflect the fact that we've uncrossed the mountpoint,
* so name had better be ours to change!
*/
static Chan*
undomount(Chan *c, Path *path)
{
Chan *nc;
if(path->ref.ref != 1 || path->mlen == 0)
print("undomount: path %s ref %ld mlen %d caller %#p\n",
path->s, path->ref, path->mlen, getcallerpc(&c));
if(path->mlen > 0 && (nc = path->mtpt[path->mlen-1]) != nil){
cclose(c);
path->mtpt[path->mlen-1] = nil;
c = nc;
}
return c;
}
/*
* Call dev walk but catch errors.
*/
static Walkqid*
ewalk(Chan *c, Chan *nc, char **name, int nname)
{
Walkqid *wq;
if(waserror())
return nil;
wq = devtab[c->type]->walk(c, nc, name, nname);
poperror();
return wq;
}
/*
* Either walks all the way or not at all. No partial results in *cp.
* *nerror is the number of names to display in an error message.
*/
int
walk(Chan **cp, char **names, int nnames, int nomount, int *nerror)
{
int dev, didmount, dotdot, i, n, nhave, ntry, type;
Chan *c, *nc, *mtpt;
Path *path;
Mhead *mh, *nmh;
Mount *f;
Walkqid *wq;
c = *cp;
incref(&c->ref);
path = c->path;
incref(&path->ref);
mh = nil;
/*
* While we haven't gotten all the way down the path:
* 1. step through a mount point, if any
* 2. send a walk request for initial dotdot or initial prefix without dotdot
* 3. move to the first mountpoint along the way.
* 4. repeat.
*
* Each time through the loop:
*
* If didmount==0, c is on the undomount side of the mount point.
* If didmount==1, c is on the domount side of the mount point.
* Either way, c's full path is path.
*/
didmount = 0;
for(nhave=0; nhave<nnames; nhave+=n){
if((c->qid.type&QTDIR) == 0){
if(nerror)
*nerror = nhave;
pathclose(path);
cclose(c);
kstrcpy(up->errstr, Enotdir, ERRMAX);
putmhead(mh);
return -1;
}
ntry = nnames - nhave;
if(ntry > MAXWELEM)
ntry = MAXWELEM;
dotdot = 0;
for(i=0; i<ntry; i++){
if(isdotdot(names[nhave+i])){
if(i==0){
dotdot = 1;
ntry = 1;
}else
ntry = i;
break;
}
}
if(!dotdot && !nomount && !didmount)
domount(&c, &mh, &path);
type = c->type;
dev = c->dev;
if((wq = ewalk(c, nil, names+nhave, ntry)) == nil){
/* try a union mount, if any */
if(mh != nil && !nomount){
/*
* mh->mount->to == c, so start at mh->mount->next
*/
rlock(&mh->lock);
if((f = mh->mount) != nil)
f = f->next;
for(; f != nil; f = f->next)
if((wq = ewalk(f->to, nil, names+nhave, ntry)) != nil){
type = f->to->type;
dev = f->to->dev;
break;
}
runlock(&mh->lock);
}
if(wq == nil){
cclose(c);
pathclose(path);
if(nerror)
*nerror = nhave+1;
putmhead(mh);
return -1;
}
}
didmount = 0;
if(dotdot){
assert(wq->nqid == 1);
assert(wq->clone != nil);
path = addelem(path, "..", nil);
nc = undomount(wq->clone, path);
nmh = nil;
n = 1;
}else{
nc = nil;
nmh = nil;
if(!nomount){
for(i=0; i<wq->nqid && i<ntry-1; i++){
if(findmount(&nc, &nmh, type, dev, wq->qid[i])){
didmount = 1;
break;
}
}
}
if(nc == nil){ /* no mount points along path */
if(wq->clone == nil){
cclose(c);
pathclose(path);
if(wq->nqid == 0 || (wq->qid[wq->nqid-1].type&QTDIR) != 0){
if(nerror)
*nerror = nhave+wq->nqid+1;
kstrcpy(up->errstr, Enonexist, ERRMAX);
}else{
if(nerror)
*nerror = nhave+wq->nqid;
kstrcpy(up->errstr, Enotdir, ERRMAX);
}
free(wq);
putmhead(mh);
return -1;
}
n = wq->nqid;
nc = wq->clone;
}else{ /* stopped early, at a mount point */
assert(didmount);
if(wq->clone != nil){
cclose(wq->clone);
wq->clone = nil;
}
n = i+1;
}
for(i=0; i<n; i++){
mtpt = nil;
if(i==n-1 && nmh!=nil)
mtpt = nmh->from;
path = addelem(path, names[nhave+i], mtpt);
}
}
cclose(c);
c = nc;
putmhead(mh);
mh = nmh;
free(wq);
}
putmhead(mh);
c = cunique(c);
pathclose(c->path);
c->path = path;
cclose(*cp);
*cp = c;
if(nerror)
*nerror = nhave;
return 0;
}
/*
* c is a mounted non-creatable directory. find a creatable one.
*/
Chan*
createdir(Chan *c, Mhead *m)
{
Chan *nc;
Mount *f;
rlock(&m->lock);
if(waserror()){
runlock(&m->lock);
nexterror();
}
for(f = m->mount; f != nil; f = f->next){
if((f->mflag&MCREATE) != 0){
nc = cclone(f->to);
runlock(&m->lock);
poperror();
cclose(c);
return nc;
}
}
error(Enocreate);
return 0;
}
void
saveregisters(void)
{
}
static void
growparse(Elemlist *e)
{
char **new;
int *inew;
enum { Delta = 8 };
if((e->nelems % Delta) == 0){
new = smalloc((e->nelems+Delta) * sizeof(char*));
memmove(new, e->elems, e->nelems*sizeof(char*));
free(e->elems);
e->elems = new;
inew = smalloc((e->nelems+Delta+1) * sizeof(int));
memmove(inew, e->off, (e->nelems+1)*sizeof(int));
free(e->off);
e->off = inew;
}
}
/*
* The name is known to be valid.
* Copy the name so slashes can be overwritten.
* An empty string will set nelem=0.
* A path ending in / or /. or /.//./ etc. will have
* e.mustbedir = 1, so that we correctly
* reject, e.g., "/adm/users/." when /adm/users is a file
* rather than a directory.
*/
static void
parsename(char *aname, Elemlist *e)
{
char *name, *slash;
kstrdup(&e->name, aname);
name = e->name;
e->nelems = 0;
e->elems = nil;
e->off = smalloc(sizeof(int));
e->off[0] = skipslash(name) - name;
for(;;){
name = skipslash(name);
if(*name == '\0'){
e->off[e->nelems] = name+strlen(name) - e->name;
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
namelenerror(char *aname, int len, char *err)
{
char *ename, *name, *next;
int i, errlen;
/*
* If the name is short enough, just use the whole thing.
*/
errlen = strlen(err);
if(len < ERRMAX/3 || len+errlen < 2*ERRMAX/3)
snprint(up->genbuf, sizeof up->genbuf, "%.*s",
utfnlen(aname, len), aname);
else{
/*
* Print a suffix of the name, but try to get a little info.
*/
ename = aname+len;
next = ename;
do{
name = next;
if(next == aname)
break;
while(next > aname)
if(*--next == '/')
break;
len = ename-next;
}while(len < ERRMAX/3 || len + errlen < 2*ERRMAX/3);
/*
* If the name is ridiculously long, chop it.
*/
if(name == ename){
name = ename-ERRMAX/4;
if(name <= aname)
panic("bad math in namelenerror");
/* walk out of current UTF sequence */
for(i=0; (*name&0xC0)==0x80 && i<UTFmax; i++)
name++;
}
snprint(up->genbuf, sizeof up->genbuf, "...%.*s",
utfnlen(name, ename-name), name);
}
snprint(up->errstr, ERRMAX, "%s: %#q", err, up->genbuf);
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 len, n, t, nomount;
Chan *volatile c;
Chan *volatile cnew;
Path *volatile path;
Elemlist e;
Rune r;
Mhead *m;
char *createerr, tmperrbuf[ERRMAX];
char *name;
if(aname[0] == '\0')
error("empty file name");
aname = validnamedup(aname, 1);
if(waserror()){
free(aname);
nexterror();
}
name = aname;
/*
* 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->ref);
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;
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->ref);
break;
}
e.aname = aname;
e.prefix = name - aname;
e.name = nil;
e.elems = nil;
e.off = nil;
e.nelems = 0;
e.nerror = 0;
if(waserror()){
cclose(c);
free(e.name);
free(e.elems);
/*
* Prepare nice error, showing first e.nerror elements of name.
*/
if(e.nerror == 0)
nexterror();
strcpy(tmperrbuf, up->errstr);
if(e.off[e.nerror]==0)
print("nerror=%d but off=%d\n",
e.nerror, e.off[e.nerror]);
len = e.prefix+e.off[e.nerror];
free(e.off);
namelenerror(aname, len, tmperrbuf);
}
/*
* Build a list of elements in the name.
*/
parsename(name, &e);
/*
* On create, ....
*/
if(amode == Acreate){
/* perm must have DMDIR if last element is / or /. */
if(e.mustbedir && !(perm&DMDIR)){
e.nerror = e.nelems;
error("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, &e.nerror) < 0){
if(e.nerror < 0 || e.nerror > e.nelems){
print("namec %s walk error nerror=%d\n", aname, e.nerror);
e.nerror = 0;
}
nexterror();
}
if(e.mustbedir && (c->qid.type&QTDIR) == 0)
error("not a directory");
if(amode == Aopen && (omode&3) == OEXEC && (c->qid.type&QTDIR) != 0)
error("cannot exec directory");
switch(amode){
case Abind:
/* no need to maintain path - cannot dotdot an Abind */
m = nil;
if(!nomount)
domount(&c, &m, nil);
if(waserror()){
putmhead(m);
nexterror();
}
c = cunique(c);
c->umh = m;
poperror();
break;
case Aaccess:
case Aremove:
case Aopen:
Open:
/* save&update the name; domount might change c */
path = c->path;
incref(&path->ref);
if(waserror()){
pathclose(path);
nexterror();
}
m = nil;
if(!nomount)
domount(&c, &m, &path);
if(waserror()){
putmhead(m);
nexterror();
}
/* our own copy to open or remove */
c = cunique(c);
poperror();
/* now it's our copy anyway, we can put the name back */
pathclose(c->path);
c->path = path;
poperror();
/* 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:
/* only save the mount head if it's a multiple element union */
if(m != nil) {
rlock(&m->lock);
if(m->mount != nil && m->mount->next != nil) {
c->umh = m;
runlock(&m->lock);
} else {
runlock(&m->lock);
putmhead(m);
}
}
/* save registers else error() in open has wrong value of c saved */
saveregisters();
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) == 0)
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++;
e.nerror++;
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->ref);
}
/*
* 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);
pathclose(cnew->path);
cnew->path = c->path;
incref(&cnew->path->ref);
cnew = 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;
putmhead(m);
cclose(c);
c = cnew;
c->path = addelem(c->path, e.elems[e.nelems-1], nil);
break;
}
/* create failed */
cclose(cnew);
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;
default:
panic("unknown namec access %d", 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(aname);
poperror(); /* aname */
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, uintptr pc)
{
char *ename, *name, *s;
int c, n;
Rune r;
name = aname;
ename = memchr(name, 0, (1<<16));
if(ename==nil || ename-name>=(1<<16))
error(Etoolong);
s = nil;
if(dup){
n = ename-name;
s = smalloc(n+1);
memmove(s, name, n);
s[n] = 0;
aname = s;
name = s;
setmalloctag(s, pc);
}
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, getcallerpc(&aname));
}
void
isdir(Chan *c)
{
if(c->qid.type & QTDIR)
return;
error(Enotdir);
}
enum
{
DIRSIZE = STATFIXLEN + 16 * 4 /* enough for encoded stat buf + some reasonable strings */
};
Dir*
dirchanstat(Chan *c)
{
Dir *d;
uchar *buf;
int n, nd, i;
nd = DIRSIZE;
for(i=0; i<2; i++){ /* should work by the second try */
d = smalloc(sizeof(Dir) + BIT16SZ + nd);
if(waserror()){
free(d);
nexterror();
}
buf = (uchar*)&d[1];
n = devtab[c->type]->stat(c, buf, BIT16SZ+nd);
if(n < BIT16SZ)
error(Eshortstat);
nd = GBIT16(buf); /* upper bound on size of Dir + strings */
if(nd <= n){
if(convM2D(buf, n, d, (char*)&d[1]) == 0)
error(Eshortstat);
poperror();
return d;
}
/* else sizeof(Dir)+BIT16SZ+nd is plenty */
free(d);
poperror();
}
error(Eshortstat);
return nil;
}