/*
* read a queue. if no data is queued, post a Block
* and wait on its Rendez.
*/
long
qread(Queue *q, void *vp, int len)
{
Block *b, *first, **l;
int m, n;
qlock(&q->rlock);
if(waserror()){
qunlock(&q->rlock);
nexterror();
}
ilock(q);
again:
switch(qwait(q)){
case 0:
/* queue closed */
iunlock(q);
qunlock(&q->rlock);
poperror();
return 0;
case -1:
/* multiple reads on a closed queue */
iunlock(q);
error(q->err);
}
/* if we get here, there's at least one block in the queue */
if(q->state & Qcoalesce){
/* when coalescing, 0 length blocks just go away */
b = q->bfirst;
if(BLEN(b) <= 0){
freeb(qremove(q));
goto again;
}
/* grab the first block plus as many
* following blocks as will completely
* fit in the read.
*/
n = 0;
l = &first;
m = BLEN(b);
for(;;) {
*l = qremove(q);
l = &b->next;
n += m;
b = q->bfirst;
if(b == nil)
break;
m = BLEN(b);
if(n+m > len)
break;
}
} else {
first = qremove(q);
n = BLEN(first);
}
/* copy to user space outside of the ilock */
iunlock(q);
b = bl2mem(vp, first, len);
ilock(q);
/* take care of any left over partial block */
if(b != nil){
n -= BLEN(b);
if(q->state & Qmsg)
freeb(b);
else
qputback(q, b);
}
/* restart producer */
qwakeup_iunlock(q);
poperror();
qunlock(&q->rlock);
return n;
}
/*
* read a queue. if no data is queued, post a struct block
* and wait on its Rendez.
*/
long qread(struct queue *q, void *vp, int len)
{
ERRSTACK(1);
struct block *b, *first, **l;
int m, n;
qlock(&q->rlock);
if (waserror()) {
qunlock(&q->rlock);
nexterror();
}
spin_lock_irqsave(&q->lock);
again:
if (!qwait(q)) {
/* queue closed */
spin_unlock_irqsave(&q->lock);
qunlock(&q->rlock);
poperror();
return 0;
}
/* if we get here, there's at least one block in the queue */
// TODO: Consider removing the Qcoalesce flag and force a coalescing
// strategy by default.
if (q->state & Qcoalesce) {
/* when coalescing, 0 length blocks just go away */
b = q->bfirst;
if (BLEN(b) <= 0) {
freeb(qremove(q));
goto again;
}
/* grab the first block plus as many
* following blocks as will completely
* fit in the read.
*/
n = 0;
l = &first;
m = BLEN(b);
for (;;) {
*l = qremove(q);
l = &b->next;
n += m;
b = q->bfirst;
if (b == NULL)
break;
m = BLEN(b);
if (n + m > len)
break;
}
} else {
first = qremove(q);
n = BLEN(first);
}
/* copy to user space outside of the ilock */
spin_unlock_irqsave(&q->lock);
b = bl2mem(vp, first, len);
spin_lock_irqsave(&q->lock);
/* take care of any left over partial block */
if (b != NULL) {
n -= BLEN(b);
if (q->state & Qmsg)
freeb(b);
else
qputback(q, b);
}
/* restart producer */
qwakeup_iunlock(q);
poperror();
qunlock(&q->rlock);
return n;
}
