* References are managed as follows:

#include "u.h"
#include "../port/lib.h"
#include "mem.h"
#include "dat.h"
#include "fns.h"
#include "../port/error.h"

/*
* References are managed as follows:
* The channel to the server - a network connection or pipe - has one
* reference for every Chan open on the server. The server channel has
* c->mux set to the Mnt used for muxing control to that server. Mnts
* have no reference count; they go away when c goes away.
* Each channel derived from the mount point has mchan set to c,
* and increfs/decrefs mchan to manage references on the server
* connection.
*/

#define MAXRPC (IOHDRSZ+8192)

struct Mntrpc
{
Chan* c; /* Channel for whom we are working */
Mntrpc* list; /* Free/pending list */
Fcall request; /* Outgoing file system protocol message */
Fcall reply; /* Incoming reply */
Mnt* m; /* Mount device during rpc */
Rendez* z; /* Place to hang out */
Block* w; /* copy of write rpc for cache */
Block* b; /* reply blocks */
Mntrpc* flushed; /* message this one flushes */
char done; /* Rpc completed */
};

enum
{
TAGSHIFT = 5,
TAGMASK = (1<<TAGSHIFT)-1,
NMASK = (64*1024)>>TAGSHIFT,
};

static struct Mntalloc
{
Lock;
Mnt* list; /* Mount devices in use */
Mnt* mntfree; /* Free list */
Mntrpc* rpcfree;
ulong nrpcfree;
ulong nrpcused;
ulong id;
u32int tagmask[NMASK];
} mntalloc;

static Chan* mntchan(void);
static Mnt* mntchk(Chan*);
static void mntdirfix(uchar*, Chan*);
static Mntrpc* mntflushalloc(Mntrpc*);
static Mntrpc* mntflushfree(Mnt*, Mntrpc*);
static void mntfree(Mntrpc*);
static void mntgate(Mnt*);
static void mntqrm(Mnt*, Mntrpc*);
static Mntrpc* mntralloc(Chan*);
static long mntrdwr(int, Chan*, void*, long, vlong);
static int mntrpcread(Mnt*, Mntrpc*);
static void mountio(Mnt*, Mntrpc*);
static void mountmux(Mnt*, Mntrpc*);
static void mountrpc(Mnt*, Mntrpc*);
static int rpcattn(void*);

#define cachedchan(c) (((c)->flag & CCACHE) != 0 && (c)->mcp != nil)

char Esbadstat[] = "invalid directory entry received from server";
char Enoversion[] = "version not established for mount channel";

static void
mntreset(void)
{
mntalloc.id = 1;
mntalloc.tagmask[0] = 1; /* don't allow 0 as a tag */
mntalloc.tagmask[NMASK-1] = 0x80000000; /* don't allow NOTAG */
fmtinstall('F', fcallfmt);
fmtinstall('D', dirfmt);
/* We can't install %M since eipfmt does and is used in the kernel [sape] */

cinit();
}

/*
* Version is not multiplexed: message sent only once per connection.
*/
int
mntversion(Chan *c, char *version, int msize, int returnlen)
{
Fcall f;
uchar *msg;
Mnt *m;
char *v;
Queue *q;
long k, l;
uvlong oo;
char buf[128];

eqlock(&c->umqlock); /* make sure no one else does this until we've established ourselves */
if(waserror()){
qunlock(&c->umqlock);
nexterror();
}

/* defaults */
if(msize == 0)
msize = MAXRPC;
if(msize > c->iounit && c->iounit != 0)
msize = c->iounit;
v = version;
if(v == nil || v[0] == '\0')
v = VERSION9P;

/* validity */
if(msize < 0)
error("bad iounit in version call");
if(strncmp(v, VERSION9P, strlen(VERSION9P)) != 0)
error("bad 9P version specification");

m = c->mux;

if(m != nil){
qunlock(&c->umqlock);
poperror();

strecpy(buf, buf+sizeof buf, m->version);
k = strlen(buf);
if(strncmp(buf, v, k) != 0){
snprint(buf, sizeof buf, "incompatible 9P versions %s %s", m->version, v);
error(buf);
}
if(returnlen > 0){
if(returnlen < k)
error(Eshort);
memmove(version, buf, k);
}
return k;
}

f.type = Tversion;
f.tag = NOTAG;
f.msize = msize;
f.version = v;
msg = malloc(8192+IOHDRSZ);
if(msg == nil)
exhausted("version memory");
if(waserror()){
free(msg);
nexterror();
}
k = convS2M(&f, msg, 8192+IOHDRSZ);
if(k == 0)
error("bad fversion conversion on send");

lock(c);
oo = c->offset;
c->offset += k;
unlock(c);

l = devtab[c->type]->write(c, msg, k, oo);
if(l < k){
lock(c);
c->offset -= k - l;
unlock(c);
error("short write in fversion");
}

/* message sent; receive and decode reply */
for(k = 0; k < BIT32SZ || (k < GBIT32(msg) && k < 8192+IOHDRSZ); k += l){
l = devtab[c->type]->read(c, msg+k, 8192+IOHDRSZ-k, c->offset);
if(l <= 0)
error("EOF receiving fversion reply");
lock(c);
c->offset += l;
unlock(c);
}

l = convM2S(msg, k, &f);
if(l != k)
error("bad fversion conversion on reply");
if(f.type != Rversion){
if(f.type == Rerror)
error(f.ename);
error("unexpected reply type in fversion");
}
if(f.msize > msize)
error("server tries to increase msize in fversion");
if(f.msize<256 || f.msize>1024*1024)
error("nonsense value of msize in fversion");
k = strlen(f.version);
if(strncmp(f.version, v, k) != 0)
error("bad 9P version returned from server");
if(returnlen > 0 && returnlen < k)
error(Eshort);

v = nil;
kstrdup(&v, f.version);
q = qopen(10*MAXRPC, 0, nil, nil);
if(q == nil){
free(v);
exhausted("mount queues");
}

/* now build Mnt associated with this connection */
lock(&mntalloc);
m = mntalloc.mntfree;
if(m != nil)
mntalloc.mntfree = m->list;
else {
unlock(&mntalloc);
m = malloc(sizeof(Mnt));
if(m == nil) {
qfree(q);
free(v);
exhausted("mount devices");
}
lock(&mntalloc);
}
m->list = mntalloc.list;
mntalloc.list = m;
m->version = v;
m->id = mntalloc.id++;
m->q = q;
m->msize = f.msize;
unlock(&mntalloc);

if(returnlen > 0)
memmove(version, f.version, k); /* length was checked above */

poperror(); /* msg */
free(msg);

lock(m);
m->queue = nil;
m->rip = nil;

c->flag |= CMSG;
c->mux = m;
m->c = c;
unlock(m);

poperror(); /* c */
qunlock(&c->umqlock);

return k;
}

Chan*
mntauth(Chan *c, char *spec)
{
Mnt *m;
Mntrpc *r;

m = c->mux;
if(m == nil){
mntversion(c, nil, 0, 0);
m = c->mux;
if(m == nil)
error(Enoversion);
}

c = mntchan();
if(waserror()) {
/* Close must not be called since it will
* call mnt recursively
*/
chanfree(c);
nexterror();
}

r = mntralloc(c);
if(waserror()) {
mntfree(r);
nexterror();
}

r->request.type = Tauth;
r->request.afid = c->fid;
r->request.uname = up->user;
r->request.aname = spec;
mountrpc(m, r);

c->qid = r->reply.aqid;
c->mchan = m->c;
incref(m->c);
c->mqid = c->qid;
c->mode = ORDWR;
c->iounit = m->msize-IOHDRSZ;

poperror(); /* r */
mntfree(r);

poperror(); /* c */

return c;

}

Chan*
mntattach(Chan *c, Chan *ac, char *spec, int flags)
{
Mnt *m;
Mntrpc *r;

if(ac != nil && ac->mchan != c)
error(Ebadusefd);

m = c->mux;
if(m == nil){
mntversion(c, nil, 0, 0);
m = c->mux;
if(m == nil)
error(Enoversion);
}

c = mntchan();
if(waserror()) {
/* Close must not be called since it will
* call mnt recursively
*/
chanfree(c);
nexterror();
}

r = mntralloc(c);
if(waserror()) {
mntfree(r);
nexterror();
}
r->request.type = Tattach;
r->request.fid = c->fid;
if(ac == nil)
r->request.afid = NOFID;
else
r->request.afid = ac->fid;
r->request.uname = up->user;
r->request.aname = spec;
mountrpc(m, r);

c->qid = r->reply.qid;
c->mchan = m->c;
incref(m->c);
c->mqid = c->qid;

poperror(); /* r */
mntfree(r);

poperror(); /* c */

if(flags&MCACHE)
c->flag |= CCACHE;
return c;
}

static Chan*
noattach(char *)
{
error(Enoattach);
return nil;
}

static Chan*
mntchan(void)
{
Chan *c;

c = devattach('M', 0);
lock(&mntalloc);
c->dev = mntalloc.id++;
unlock(&mntalloc);

if(c->mchan != nil)
panic("mntchan non-zero %p", c->mchan);
return c;
}

static Walkqid*
mntwalk(Chan *c, Chan *nc, char **name, int nname)
{
int i, alloc;
Mnt *m;
Mntrpc *r;
Walkqid *wq;

if(nc != nil)
print("mntwalk: nc != nil\n");
if(nname > MAXWELEM)
error("devmnt: too many name elements");
alloc = 0;
wq = smalloc(sizeof(Walkqid)+(nname-1)*sizeof(Qid));
if(waserror()){
if(alloc && wq->clone!=nil)
cclose(wq->clone);
free(wq);
return nil;
}

alloc = 0;
m = mntchk(c);
r = mntralloc(c);
if(nc == nil){
nc = devclone(c);
/*
* Until the other side accepts this fid, we can't mntclose it.
* Therefore set type to 0 for now; rootclose is known to be safe.
*/
nc->type = 0;
nc->flag |= (c->flag & CCACHE);
alloc = 1;
}
wq->clone = nc;

if(waserror()) {
mntfree(r);
nexterror();
}
r->request.type = Twalk;
r->request.fid = c->fid;
r->request.newfid = nc->fid;
r->request.nwname = nname;
memmove(r->request.wname, name, nname*sizeof(char*));

mountrpc(m, r);

if(r->reply.nwqid > nname)
error("too many QIDs returned by walk");
if(r->reply.nwqid < nname){
if(alloc)
cclose(nc);
wq->clone = nil;
if(r->reply.nwqid == 0){
free(wq);
wq = nil;
goto Return;
}
}

/* move new fid onto mnt device and update its qid */
if(wq->clone != nil){
if(wq->clone != c){
wq->clone->type = c->type;
wq->clone->mchan = c->mchan;
incref(c->mchan);
}
if(r->reply.nwqid > 0)
wq->clone->qid = r->reply.wqid[r->reply.nwqid-1];
}
wq->nqid = r->reply.nwqid;
for(i=0; i<wq->nqid; i++)
wq->qid[i] = r->reply.wqid[i];

Return:
poperror();
mntfree(r);
poperror();
return wq;
}

static int
mntstat(Chan *c, uchar *dp, int n)
{
Mnt *m;
Mntrpc *r;

if(n < BIT16SZ)
error(Eshortstat);
m = mntchk(c);
r = mntralloc(c);
if(waserror()) {
mntfree(r);
nexterror();
}
r->request.type = Tstat;
r->request.fid = c->fid;
mountrpc(m, r);

if(r->reply.nstat > n){
n = BIT16SZ;
PBIT16((uchar*)dp, r->reply.nstat-2);
}else{
n = r->reply.nstat;
memmove(dp, r->reply.stat, n);
validstat(dp, n);
mntdirfix(dp, c);
}
poperror();
mntfree(r);
return n;
}

static Chan*
mntopencreate(int type, Chan *c, char *name, int omode, ulong perm)
{
Mnt *m;
Mntrpc *r;

m = mntchk(c);
r = mntralloc(c);
if(waserror()) {
mntfree(r);
nexterror();
}
r->request.type = type;
r->request.fid = c->fid;
r->request.mode = omode;
if(type == Tcreate){
r->request.perm = perm;
r->request.name = name;
}
mountrpc(m, r);

c->qid = r->reply.qid;
c->offset = 0;
c->mode = openmode(omode);
c->iounit = r->reply.iounit;
if(c->iounit == 0 || c->iounit > m->msize-IOHDRSZ)
c->iounit = m->msize-IOHDRSZ;
c->flag |= COPEN;
poperror();
mntfree(r);

if(c->flag & CCACHE){
if(copen(c))
if(type == Tcreate || (omode&OTRUNC) != 0)
ctrunc(c);
}

return c;
}

static Chan*
mntopen(Chan *c, int omode)
{
return mntopencreate(Topen, c, nil, omode, 0);
}

static Chan*
mntcreate(Chan *c, char *name, int omode, ulong perm)
{
return mntopencreate(Tcreate, c, name, omode, perm);
}

static void
mntclunk(Chan *c, int t)
{
Mnt *m;
Mntrpc *r;

cclunk(c);
m = mntchk(c);
r = mntralloc(c);
if(waserror()) {
mntfree(r);
nexterror();
}
r->request.type = t;
r->request.fid = c->fid;
mountrpc(m, r);
mntfree(r);
poperror();
}

void
muxclose(Mnt *m)
{
Mnt *f, **l;
Mntrpc *r;

while((r = m->queue) != nil){
m->queue = r->list;
mntfree(r);
}
m->id = 0;
free(m->version);
m->version = nil;
qfree(m->q);
m->q = nil;

lock(&mntalloc);
l = &mntalloc.list;
for(f = *l; f != nil; f = f->list) {
if(f == m) {
*l = m->list;
break;
}
l = &f->list;
}
m->list = mntalloc.mntfree;
mntalloc.mntfree = m;
unlock(&mntalloc);
}

static void
mntclose(Chan *c)
{
mntclunk(c, Tclunk);
}

static void
mntremove(Chan *c)
{
mntclunk(c, Tremove);
}

static int
mntwstat(Chan *c, uchar *dp, int n)
{
Mnt *m;
Mntrpc *r;

m = mntchk(c);
r = mntralloc(c);
if(waserror()) {
mntfree(r);
nexterror();
}
r->request.type = Twstat;
r->request.fid = c->fid;
r->request.nstat = n;
r->request.stat = dp;
mountrpc(m, r);
poperror();
mntfree(r);

if(c->flag & CCACHE)
if(GBIT64(&dp[STATFIXLEN-4*BIT16SZ-BIT64SZ]) != ~0ULL)
ctrunc(c);

return n;
}

static long
mntread(Chan *c, void *buf, long n, vlong off)
{
uchar *p, *e;
int dirlen;

p = buf;
n = mntrdwr(Tread, c, p, n, off);
if(c->qid.type & QTDIR) {
for(e = &p[n]; p+BIT16SZ < e; p += dirlen){
dirlen = BIT16SZ+GBIT16(p);
if(p+dirlen > e)
break;
validstat(p, dirlen);
mntdirfix(p, c);
}
if(p != e)
error(Esbadstat);
}
return n;
}

static long
mntwrite(Chan *c, void *buf, long n, vlong off)
{
return mntrdwr(Twrite, c, buf, n, off);
}

static void
mntcache(Mntrpc *r)
{
ulong n, m;
vlong off;
Block *b;
Chan *c;

c = r->c;
if(!cachedchan(c))
return;
off = r->request.offset;
switch(r->reply.type){
case Rread:
m = r->reply.count;
if(m > r->request.count)
m = r->request.count;
for(b = r->b; m > 0 && b != nil; m -= n, b = b->next) {
n = BLEN(b);
if(m < n)
n = m;
cupdate(c, b->rp, n, off);
off += n;
}
break;
case Rwrite:
b = r->w;
if(convM2S(b->rp, BLEN(b), &r->request) == 0)
panic("convM2S");
m = r->reply.count;
if(m > r->request.count)
m = r->request.count;
cwrite(c, (uchar*)r->request.data, m, off);
break;
}
}

static long
mntrdwr(int type, Chan *c, void *buf, long n, vlong off)
{
Mnt *m;
Mntrpc *r;
char *uba;
ulong cnt, nr, nreq;

m = mntchk(c);
uba = buf;
cnt = 0;

for(;;) {
nreq = n;
if(nreq > c->iounit)
nreq = c->iounit;

if(type == Tread && cachedchan(c)) {
nr = cread(c, (uchar*)uba, nreq, off);
if(nr > 0) {
nreq = nr;
goto Next;
}
}

r = mntralloc(c);
if(waserror()) {
mntfree(r);
nexterror();
}
r->request.type = type;
r->request.fid = c->fid;
r->request.offset = off;
r->request.data = uba;
r->request.count = nreq;
mountrpc(m, r);
mntcache(r);
nr = r->reply.count;
if(nr > nreq)
nr = nreq;
if(type == Tread)
nr = readblist(r->b, (uchar*)uba, nr, 0);
mntfree(r);
poperror();

Next:
off += nr;
uba += nr;
cnt += nr;
n -= nr;
if(nr != nreq || n == 0 || up->nnote)
break;
}
return cnt;
}

static int
mntprocwork(void *a)
{
Mntproc *p = a;
return p->f != nil;
}

static void
mntproc(void *a)
{
Mntproc *p = a;
Chan *c;
Mnt *m;

while(waserror())
;

m = p->m;
for(;;){
tsleep(p, mntprocwork, p, 500);

lock(m);
if(p->f == nil){
p->m = nil;
unlock(m);
pexit("no work", 1);
}
c = p->r->c;
unlock(m);

(*p->f)(p->r, p->a);

lock(m);
p->r = nil;
p->a = nil;
p->f = nil;
unlock(m);

cclose(c);
}
}

static int
mntdefer(void (*f)(Mntrpc*, void*), Mntrpc *r, void *a)
{
Mntproc *p;
Mnt *m;
int i;

m = mntchk(r->c);
lock(m);
for(i = 0; i < nelem(m->defered); i++){
p = &m->defered[i];
if(p->f != nil)
continue;

incref(r->c);
r->m = m;
p->r = r;
p->a = a;
p->f = f;

if(p->m == nil){
p->m = m;
unlock(m);
kproc("mntproc", mntproc, p);
} else {
unlock(m);
wakeup(p);
}
return 1;
}
unlock(m);
return 0;
}

static void
rahproc(Mntrpc *r, void *a)
{
Mntrah *rah = a;

if(!waserror()){
mountrpc(r->m, r);
poperror();
}
r->done = 2;
wakeup(rah);
}

static int
rahdone(void *v)
{
Mntrpc *r = v;
return r->done == 2;
}

static Mntrpc*
rahfindrpc(Mntrah *rah, vlong off)
{
Mntrpc *r;
int i, n;
vlong o;

for(i=0; i<nelem(rah->r); i++){
if((r = rah->r[i]) == nil)
continue;
n = r->request.count;
o = r->request.offset;
if(off >= o && off < o+n)
return r;
}
return nil;
}

void
mntrahinit(Mntrah *rah)
{
Mntrpc *r;
int i;

while(waserror())
;

for(i=0; i<nelem(rah->r); i++){
if((r = rah->r[i]) != nil){
while(!rahdone(r))
sleep(rah, rahdone, r);
rah->r[i] = nil;
mntfree(r);
}
}
rah->i = 0;

rah->off = 0;
rah->seq = 0;

poperror();
}

long
mntrahread(Mntrah *rah, Chan *c, uchar *buf, long len, vlong off)
{
Mntrpc *r, **rr;
vlong o, w, e;
long n, tot;

if(len <= 0)
return 0;
if(off != rah->off){
rah->off = off;
if(rahfindrpc(rah, off) == nil)
rah->seq = 0;
}
rah->off += len;
rah->seq += len;
if(rah->seq >= 2*c->iounit){
w = (off / c->iounit) * c->iounit;
e = w + rah->seq;
for(o = w; o < e; o += c->iounit){
if(rahfindrpc(rah, o) != nil)
continue;

rr = &rah->r[rah->i % nelem(rah->r)];
if((r = *rr) != nil){
if(!rahdone(r) || (r->request.offset >= w && r->request.offset < e))
break;
*rr = nil;
mntfree(r);
}

r = mntralloc(c);
r->request.type = Tread;
r->request.fid = c->fid;
r->request.offset = o;
r->request.count = c->iounit;
if(!mntdefer(rahproc, r, rah)){
mntfree(r);
break;
}
*rr = r;
rah->i++;
}
}

tot = 0;
while(len > 0 && (r = rahfindrpc(rah, off)) != nil){
while(!rahdone(r))
sleep(rah, rahdone, r);

switch(r->reply.type){
default:
error(Emountrpc);
case Rflush:
error(Eintr);
case Rerror:
error(r->reply.ename);
case Rread:
break;
}
mntcache(r);
n = r->request.count;
o = r->request.offset;
if(r->reply.count < n)
n = r->reply.count;
n -= (off - o);
if(n <= 0)
break;
if(len < n)
n = len;
n = readblist(r->b, buf, n, off - o);
buf += n;
off += n;
tot += n;
len -= n;
}
if(tot > 0){
rah->off -= len;
rah->seq -= len;
}

return tot;
}

static void
mountrpc(Mnt *m, Mntrpc *r)
{
int t;

r->reply.tag = 0;
r->reply.type = Tmax; /* can't ever be a valid message type */

mountio(m, r);

t = r->reply.type;
switch(t) {
case Rerror:
error(r->reply.ename);
case Rflush:
error(Eintr);
default:
if(t == r->request.type+1)
break;
print("mnt: proc %s %lud: mismatch from %s %s rep %#p tag %d fid %d T%d R%d rp %d\n",
up->text, up->pid, chanpath(m->c), chanpath(r->c),
r, r->request.tag, r->request.fid, r->request.type,
r->reply.type, r->reply.tag);
error(Emountrpc);
}
}

static void
mountio(Mnt *m, Mntrpc *r)
{
Block *b;
int n;

while(waserror()) {
if(m->rip == up)
mntgate(m);
if(strcmp(up->errstr, Eintr) != 0 || waserror()){
r = mntflushfree(m, r);
switch(r->request.type){
case Tremove:
case Tclunk:
/* botch, abandon fid */
if(strcmp(up->errstr, Ehungup) != 0)
r->c->fid = 0;
}
nexterror();
}
r = mntflushalloc(r);
poperror();
}

lock(m);
r->z = &up->sleep;
r->m = m;
r->list = m->queue;
m->queue = r;
unlock(m);

/* Transmit a file system rpc */
n = sizeS2M(&r->request);
b = allocb(n);
if(waserror()){
freeb(b);
nexterror();
}
n = convS2M(&r->request, b->wp, n);
if(n <= 0 || n > m->msize) {
print("mountio: proc %s %lud: convS2M returned %d for tag %d fid %d T%d\n",
up->text, up->pid, n, r->request.tag, r->request.fid, r->request.type);
error(Emountrpc);
}
b->wp += n;
if(r->request.type == Twrite && cachedchan(r->c))
r->w = copyblock(b, n);
poperror();
devtab[m->c->type]->bwrite(m->c, b, 0);

/* Gate readers onto the mount point one at a time */
for(;;) {
lock(m);
if(m->rip == nil)
break;
unlock(m);
sleep(r->z, rpcattn, r);
if(r->done) {
poperror();
mntflushfree(m, r);
return;
}
}
m->rip = up;
unlock(m);
while(r->done == 0) {
if(mntrpcread(m, r) < 0)
error(Emountrpc);
mountmux(m, r);
}
mntgate(m);
poperror();
mntflushfree(m, r);
}

static int
doread(Mnt *m, int len)
{
Block *b;

while(qlen(m->q) < len){
b = devtab[m->c->type]->bread(m->c, m->msize, 0);
if(b == nil || qaddlist(m->q, b) == 0)
return -1;
}
return 0;
}

static int
mntrpcread(Mnt *m, Mntrpc *r)
{
int i, t, len, hlen;
Block *b, **l, *nb;

r->reply.type = 0;
r->reply.tag = 0;

/* read at least length, type, and tag and pullup to a single block */
if(doread(m, BIT32SZ+BIT8SZ+BIT16SZ) < 0)
return -1;
nb = pullupqueue(m->q, BIT32SZ+BIT8SZ+BIT16SZ);

/* read in the rest of the message, avoid ridiculous (for now) message sizes */
len = GBIT32(nb->rp);
if(len > m->msize){
qdiscard(m->q, qlen(m->q));
return -1;
}
if(doread(m, len) < 0)
return -1;

/* pullup the header (i.e. everything except data) */
t = nb->rp[BIT32SZ];
switch(t){
case Rread:
hlen = BIT32SZ+BIT8SZ+BIT16SZ+BIT32SZ;
break;
default:
hlen = len;
break;
}
nb = pullupqueue(m->q, hlen);

if(convM2S(nb->rp, len, &r->reply) <= 0){
/* bad message, dump it */
print("mntrpcread: convM2S failed\n");
qdiscard(m->q, len);
return -1;
}

/* hang the data off of the fcall struct */
l = &r->b;
*l = nil;
do {
b = qremove(m->q);
if(hlen > 0){
b->rp += hlen;
len -= hlen;
hlen = 0;
}
i = BLEN(b);
if(i <= len){
len -= i;
*l = b;
l = &(b->next);
} else {
/* split block and put unused bit back */
nb = allocb(i-len);
memmove(nb->wp, b->rp+len, i-len);
b->wp = b->rp+len;
nb->wp += i-len;
qputback(m->q, nb);
*l = b;
return 0;
}
}while(len > 0);

return 0;
}

static void
mntgate(Mnt *m)
{
Mntrpc *q;

lock(m);
m->rip = nil;
for(q = m->queue; q != nil; q = q->list) {
if(q->done == 0)
if(wakeup(q->z))
break;
}
unlock(m);
}

static void
mountmux(Mnt *m, Mntrpc *r)
{
Mntrpc **l, *q;
Rendez *z;

lock(m);
l = &m->queue;
for(q = *l; q != nil; q = q->list) {
/* look for a reply to a message */
if(q->request.tag == r->reply.tag) {
*l = q->list;
if(q == r) {
q->done = 1;
unlock(m);
return;
}
/*
* Completed someone else.
* Trade pointers to receive buffer.
*/
q->reply = r->reply;
q->b = r->b;
r->b = nil;
z = q->z;
coherence();
q->done = 1;
wakeup(z);
unlock(m);
return;
}
l = &q->list;
}
unlock(m);
print("unexpected reply tag %ud; type %d\n", r->reply.tag, r->reply.type);
}

/*
* Create a new flush request and chain the previous
* requests from it
*/
static Mntrpc*
mntflushalloc(Mntrpc *r)
{
Mntrpc *fr;

fr = mntralloc(r->c);
fr->request.type = Tflush;
if(r->request.type == Tflush)
fr->request.oldtag = r->request.oldtag;
else
fr->request.oldtag = r->request.tag;
fr->flushed = r;

return fr;
}

/*
* Free a chain of flushes. Remove each unanswered
* flush and the original message from the unanswered
* request queue. Mark the original message as done
* and if it hasn't been answered set the reply to to
* Rflush. Return the original rpc.
*/
static Mntrpc*
mntflushfree(Mnt *m, Mntrpc *r)
{
Mntrpc *fr;

while(r != nil){
fr = r->flushed;
if(!r->done){
r->reply.type = Rflush;
mntqrm(m, r);
}
if(fr == nil)
break;
mntfree(r);
r = fr;
}
return r;
}

static int
alloctag(void)
{
int i, j;
u32int v;

for(i = 0; i < NMASK; i++){
v = mntalloc.tagmask[i];
if(v == -1)
continue;
for(j = 0; (v & 1) != 0; j++)
v >>= 1;
mntalloc.tagmask[i] |= 1<<j;
return i<<TAGSHIFT | j;
}
panic("no friggin tags left");
return NOTAG;
}

static void
freetag(int t)
{
mntalloc.tagmask[t>>TAGSHIFT] &= ~(1<<(t&TAGMASK));
}

static Mntrpc*
mntralloc(Chan *c)
{
Mntrpc *new;

if(mntalloc.nrpcfree == 0) {
Alloc:
new = malloc(sizeof(Mntrpc));
if(new == nil)
exhausted("mount rpc header");
lock(&mntalloc);
new->request.tag = alloctag();
} else {
lock(&mntalloc);
new = mntalloc.rpcfree;
if(new == nil) {
unlock(&mntalloc);
goto Alloc;
}
mntalloc.rpcfree = new->list;
mntalloc.nrpcfree--;
}
mntalloc.nrpcused++;
unlock(&mntalloc);
new->c = c;
new->done = 0;
new->flushed = nil;
new->b = nil;
new->w = nil;
return new;
}

static void
mntfree(Mntrpc *r)
{
freeb(r->w);
freeblist(r->b);
lock(&mntalloc);
mntalloc.nrpcused--;
if(mntalloc.nrpcfree < 32) {
r->list = mntalloc.rpcfree;
mntalloc.rpcfree = r;
mntalloc.nrpcfree++;
unlock(&mntalloc);
return;
}
freetag(r->request.tag);
unlock(&mntalloc);
free(r);
}

static void
mntqrm(Mnt *m, Mntrpc *r)
{
Mntrpc **l, *f;

lock(m);
r->done = 1;

l = &m->queue;
for(f = *l; f != nil; f = f->list) {
if(f == r) {
*l = r->list;
break;
}
l = &f->list;
}
unlock(m);
}

static Mnt*
mntchk(Chan *c)
{
Mnt *m;

/* This routine is mostly vestiges of prior lives; now it's just sanity checking */
if(c->mchan == nil)
panic("mntchk 1: nil mchan c %s", chanpath(c));

m = c->mchan->mux;
if(m == nil)
print("mntchk 2: nil mux c %s c->mchan %s \n", chanpath(c), chanpath(c->mchan));

/*
* Was it closed and reused (was error(Eshutdown); now, it cannot happen)
*/
if(m->id == 0 || m->id >= c->dev)
panic("mntchk 3: can't happen");

return m;
}

/*
* Rewrite channel type and dev for in-flight data to
* reflect local values. These entries are known to be
* the first two in the Dir encoding after the count.
*/
static void
mntdirfix(uchar *dirbuf, Chan *c)
{
uint r;

r = devtab[c->type]->dc;
dirbuf += BIT16SZ; /* skip count */
PBIT16(dirbuf, r);
dirbuf += BIT16SZ;
PBIT32(dirbuf, c->dev);
}

static int
rpcattn(void *v)
{
Mntrpc *r;

r = v;
return r->done || r->m->rip == nil;
}

Dev mntdevtab = {
'M',
"mnt",

mntreset,
devinit,
devshutdown,
noattach,
mntwalk,
mntstat,
mntopen,
mntcreate,
mntclose,
mntread,
devbread,
mntwrite,
devbwrite,
mntremove,
mntwstat,
};