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/*
* Multiplexed Venti client. It would be nice if we
* could turn this into a generic library routine rather
* than keep it Venti specific. A user-level 9P client
* could use something like this too.
*
* (Actually it does - this should be replaced with libmux,
* which should be renamed librpcmux.)
*
* This is a little more complicated than it might be
* because we want it to work well within and without libthread.
*
* The mux code is inspired by tra's, which is inspired by the Plan 9 kernel.
*/
#include <u.h>
#include <libc.h>
#include <venti.h>
typedef struct Rwait Rwait;
struct Rwait
{
Rendez r;
Packet *p;
int done;
int sleeping;
};
static int gettag(VtConn*, Rwait*);
static void puttag(VtConn*, Rwait*, int);
static void muxrpc(VtConn*, Packet*);
Packet*
_vtrpc(VtConn *z, Packet *p, VtFcall *tx)
{
int i;
uchar tag, buf[2], *top;
Rwait *r, *rr;
/* must malloc because stack could be private */
r = vtmallocz(sizeof(Rwait));
qlock(&z->lk);
r->r.l = &z->lk;
tag = gettag(z, r);
if(tx){
/* vtfcallrpc can't print packet because it doesn't have tag */
tx->tag = tag;
if(chattyventi)
fprint(2, "%s -> %F\n", argv0, tx);
}
/* slam tag into packet */
top = packetpeek(p, buf, 0, 2);
if(top == nil){
packetfree(p);
return nil;
}
if(top == buf){
werrstr("first two bytes must be in same packet fragment");
packetfree(p);
vtfree(r);
return nil;
}
top[1] = tag;
qunlock(&z->lk);
if(vtsend(z, p) < 0){
vtfree(r);
return nil;
}
qlock(&z->lk);
/* wait for the muxer to give us our packet */
r->sleeping = 1;
z->nsleep++;
while(z->muxer && !r->done)
rsleep(&r->r);
z->nsleep--;
r->sleeping = 0;
/* if not done, there's no muxer: start muxing */
if(!r->done){
if(z->muxer)
abort();
z->muxer = 1;
while(!r->done){
qunlock(&z->lk);
if((p = vtrecv(z)) == nil){
werrstr("unexpected eof on venti connection");
z->muxer = 0;
vtfree(r);
return nil;
}
qlock(&z->lk);
muxrpc(z, p);
}
z->muxer = 0;
/* if there is anyone else sleeping, wake first unfinished to mux */
if(z->nsleep)
for(i=0; i<256; i++){
rr = z->wait[i];
if(rr && rr->sleeping && !rr->done){
rwakeup(&rr->r);
break;
}
}
}
p = r->p;
puttag(z, r, tag);
vtfree(r);
qunlock(&z->lk);
return p;
}
Packet*
vtrpc(VtConn *z, Packet *p)
{
return _vtrpc(z, p, nil);
}
static int
gettag(VtConn *z, Rwait *r)
{
int i;
Again:
while(z->ntag == 256)
rsleep(&z->tagrend);
for(i=0; i<256; i++)
if(z->wait[i] == 0){
z->ntag++;
z->wait[i] = r;
return i;
}
fprint(2, "libventi: ntag botch\n");
goto Again;
}
static void
puttag(VtConn *z, Rwait *r, int tag)
{
assert(z->wait[tag] == r);
z->wait[tag] = nil;
z->ntag--;
rwakeup(&z->tagrend);
}
static void
muxrpc(VtConn *z, Packet *p)
{
uchar tag, buf[2], *top;
Rwait *r;
if((top = packetpeek(p, buf, 0, 2)) == nil){
fprint(2, "libventi: short packet in vtrpc\n");
packetfree(p);
return;
}
tag = top[1];
if((r = z->wait[tag]) == nil){
fprint(2, "libventi: unexpected packet tag %d in vtrpc\n", tag);
abort();
packetfree(p);
return;
}
r->p = p;
r->done = 1;
rwakeup(&r->r);
}
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