qio.c

在x86平台上运行不可信任代码的sandbox。

		b = b->next;
	}

	/* copy bytes from there */
	for(sofar = 0; sofar < len;){
		if(n > len - sofar)
			n = len - sofar;
		memmove(nb->wp, p, n);
		qcopycnt += n;
		sofar += n;
		nb->wp += n;
		b = b->next;
		if(b == nil)
			break;
		n = BLEN(b);
		p = b->rp;
	}
	iunlock(&q->lk);

	return nb;
}

/*
 *  called by non-interrupt code
 */
Queue*
qopen(int limit, int msg, void (*kick)(void*), void *arg)
{
	Queue *q;

	q = malloc(sizeof(Queue));
	if(q == 0)
		return 0;

	q->limit = q->inilim = limit;
	q->kick = kick;
	q->arg = arg;
	q->state = msg;
	
	q->state |= Qstarve;
	q->eof = 0;
	q->noblock = 0;

	return q;
}

/* open a queue to be bypassed */
Queue*
qbypass(void (*bypass)(void*, Block*), void *arg)
{
	Queue *q;

	q = malloc(sizeof(Queue));
	if(q == 0)
		return 0;

	q->limit = 0;
	q->arg = arg;
	q->bypass = bypass;
	q->state = 0;

	return q;
}

static int
notempty(void *a)
{
	Queue *q = a;

	return (q->state & Qclosed) || q->bfirst != 0;
}

/*
 *  wait for the queue to be non-empty or closed.
 *  called with q ilocked.
 */
static int
qwait(Queue *q)
{
	/* wait for data */
	for(;;){
		if(q->bfirst != nil)
			break;

		if(q->state & Qclosed){
			if(++q->eof > 3)
				return -1;
			if(*q->err && strcmp(q->err, Ehungup) != 0)
				return -1;
			return 0;
		}

		q->state |= Qstarve;	/* flag requesting producer to wake me */
		iunlock(&q->lk);
		sleep(&q->rr, notempty, q);
		ilock(&q->lk);
	}
	return 1;
}

/*
 * add a block list to a queue
 */
void
qaddlist(Queue *q, Block *b)
{
	/* queue the block */
	if(q->bfirst)
		q->blast->next = b;
	else
		q->bfirst = b;
	q->len += blockalloclen(b);
	q->dlen += blocklen(b);
	while(b->next)
		b = b->next;
	q->blast = b;
}

/*
 *  called with q ilocked
 */
Block*
qremove(Queue *q)
{
	Block *b;

	b = q->bfirst;
	if(b == nil)
		return nil;
	q->bfirst = b->next;
	b->next = nil;
	q->dlen -= BLEN(b);
	q->len -= BALLOC(b);
	QDEBUG checkb(b, "qremove");
	return b;
}

/*
 *  copy the contents of a string of blocks into
 *  memory.  emptied blocks are freed.  return
 *  pointer to first unconsumed block.
 */
Block*
bl2mem(uchar *p, Block *b, int n)
{
	int i;
	Block *next;

	for(; b != nil; b = next){
		i = BLEN(b);
		if(i > n){
			memmove(p, b->rp, n);
			b->rp += n;
			return b;
		}
		memmove(p, b->rp, i);
		n -= i;
		p += i;
		b->rp += i;
		next = b->next;
		freeb(b);
	}
	return nil;
}

/*
 *  copy the contents of memory into a string of blocks.
 *  return nil on error.
 */
Block*
mem2bl(uchar *p, int len)
{
	int n;
	Block *b, *first, **l;

	first = nil;
	l = &first;
	if(waserror()){
		freeblist(first);
		nexterror();
	}
	do {
		n = len;
		if(n > Maxatomic)
			n = Maxatomic;

		*l = b = allocb(n);
		memmove(b->wp, p, n);
		b->wp += n;
		p += n;
		len -= n;
		l = &b->next;
	} while(len > 0);
	poperror();

	return first;
}

/*
 *  put a block back to the front of the queue
 *  called with q ilocked
 */
void
qputback(Queue *q, Block *b)
{
	b->next = q->bfirst;
	if(q->bfirst == nil)
		q->blast = b;
	q->bfirst = b;
	q->len += BALLOC(b);
	q->dlen += BLEN(b);
}

/*
 *  flow control, get producer going again
 *  called with q ilocked
 */
static void
qwakeup_iunlock(Queue *q)
{
	int dowakeup = 0;

	/* if writer flow controlled, restart */
	if((q->state & Qflow) && q->len < q->limit/2){
		q->state &= ~Qflow;
		dowakeup = 1;
	}

	iunlock(&q->lk);

	/* wakeup flow controlled writers */
	if(dowakeup){
		if(q->kick)
			q->kick(q->arg);
		wakeup(&q->wr);
	}
}

/*
 *  get next block from a queue (up to a limit)
 */
Block*
qbread(Queue *q, int len)
{
	Block *b, *nb;
	int n;

	qlock(&q->rlock);
	if(waserror()){
		qunlock(&q->rlock);
		nexterror();
	}

	ilock(&q->lk);
	switch(qwait(q)){
	case 0:
		/* queue closed */
		iunlock(&q->lk);
		qunlock(&q->rlock);
		poperror();
		return nil;
	case -1:
		/* multiple reads on a closed queue */
		iunlock(&q->lk);
		error(q->err);
	}

	/* if we get here, there's at least one block in the queue */
	b = qremove(q);
	n = BLEN(b);

	/* split block if it's too big and this is not a message queue */
	nb = b;
	if(n > len){
		if((q->state&Qmsg) == 0){
			n -= len;
			b = allocb(n);
			memmove(b->wp, nb->rp+len, n);
			b->wp += n;
			qputback(q, b);
		}
		nb->wp = nb->rp + len;
	}

	/* restart producer */
	qwakeup_iunlock(q);

	poperror();
	qunlock(&q->rlock);
	return nb;
}

/*
 *  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->lk);
again:
	switch(qwait(q)){
	case 0:
		/* queue closed */
		iunlock(&q->lk);
		qunlock(&q->rlock);
		poperror();
		return 0;
	case -1:
		/* multiple reads on a closed queue */
		iunlock(&q->lk);
		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->lk);
	b = bl2mem(vp, first, len);
	ilock(&q->lk);

	/* 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;
}

static int
qnotfull(void *a)
{
	Queue *q = a;

	return q->len < q->limit || (q->state & Qclosed);
}

ulong noblockcnt;

/*
 *  add a block to a queue obeying flow control
 */
long
qbwrite(Queue *q, Block *b)
{
	int n, dowakeup;
	Proc *p;

	n = BLEN(b);

	if(q->bypass){
		(*q->bypass)(q->arg, b);
		return n;
	}

	dowakeup = 0;
	qlock(&q->wlock);
	if(waserror()){
		if(b != nil)
			freeb(b);
		qunlock(&q->wlock);
		nexterror();
	}

	ilock(&q->lk);

	/* give up if the queue is closed */
	if(q->state & Qclosed){
		iunlock(&q->lk);
		error(q->err);
	}

	/* if nonblocking, don't queue over the limit */
	if(q->len >= q->limit){
		if(q->noblock){
			iunlock(&q->lk);
			freeb(b);
			noblockcnt += n;
			qunlock(&q->wlock);
			poperror();
			return n;
		}
	}

	/* queue the block */
	if(q->bfirst)
		q->blast->next = b;
	else
		q->bfirst = b;
	q->blast = b;
	b->next = 0;
	q->len += BALLOC(b);
	q->dlen += n;
	QDEBUG checkb(b, "qbwrite");
	b = nil;

	/* make sure other end gets awakened */
	if(q->state & Qstarve){
		q->state &= ~Qstarve;
		dowakeup = 1;
	}
	iunlock(&q->lk);

	/*  get output going again */
	if(q->kick && (dowakeup || (q->state&Qkick)))
		q->kick(q->arg);

	/* wakeup anyone consuming at the other end */
	if(dowakeup){
		p = wakeup(&q->rr);

		/* if we just wokeup a higher priority process, let it run */
		if(p != nil && p->priority > up->priority)
			sched();
	}

	/*
	 *  flow control, wait for queue to get below the limit
	 *  before allowing the process to continue and queue
	 *  more.  We do this here so that postnote can only
	 *  interrupt us after the data has been queued.  This
	 *  means that things like 9p flushes and ssl messages
	 *  will not be disrupted by software interrupts.
	 *
	 *  Note - this is moderately dangerous since a process
	 *  that keeps getting interrupted and rewriting will
	 *  queue infinite crud.
	 */
	for(;;){
		if(q->noblock || qnotfull(q))
			break;

		ilock(&q->lk);
		q->state |= Qflow;
		iunlock(&q->lk);
		sleep(&q->wr, qnotfull, q);
	}
	USED(b);

	qunlock(&q->wlock);
	poperror();
	return n;
}

/*
 *  write to a queue.  only Maxatomic bytes at a time is atomic.
 */
int
qwrite(Queue *q, void *vp, int len)
{
	int n, sofar;
	Block *b;
	uchar *p = vp;

	QDEBUG if(!islo())
		print("qwrite hi %lux\n", getcallerpc(&q));

	sofar = 0;
	do {
		n = len-sofar;
		if(n > Maxatomic)
			n = Maxatomic;

		b = allocb(n);
		if(waserror()){
			freeb(b);
			nexterror();
		}
		memmove(b->wp, p+sofar, n);
		poperror();
		b->wp += n;

		qbwrite(q, b);

		sofar += n;
	} while(sofar < len && (q->state & Qmsg) == 0);

	return len;
}

/*
 *  used by print() to write to a queue.  Since we may be splhi or not in
 *  a process, don't qlock.
 *
 *  this routine merges adjacent blocks if block n+1 will fit into
 *  the free space of block n.
 */
int
qiwrite(Queue *q, void *vp, int len)
{
	int n, sofar, dowakeup;
	Block *b;
	uchar *p = vp;

	dowakeup = 0;

	sofar = 0;
	do {
		n = len-sofar;
		if(n > Maxatomic)
			n = Maxatomic;

		b = iallocb(n);
		if(b == nil)
			break;
		memmove(b->wp, p+sofar, n);
		b->wp += n;

		ilock(&q->lk);

		/* we use an artificially high limit for kernel prints since anything
		 * over the limit gets dropped
		 */
		if(q->dlen >= 16*1024){
			iunlock(&q->lk);
			freeb(b);
			break;
		}

		QDEBUG checkb(b, "qiwrite");
		if(q->bfirst)
			q->blast->next = b;
		else
			q->bfirst = b;
		q->blast = b;
		q->len += BALLOC(b);
		q->dlen += n;

		if(q->state & Qstarve){
			q->state &= ~Qstarve;
			dowakeup = 1;
		}

		iunlock(&q->lk);

		if(dowakeup){
			if(q->kick)
				q->kick(q->arg);
			wakeup(&q->rr);
		}

		sofar += n;
	} while(sofar < len && (q->state & Qmsg) == 0);

	return sofar;
}

/*
 *  be extremely careful when calling this,
 *  as there is no reference accounting
 */
void
qfree(Queue *q)
{
	qclose(q);
	free(q);
}

/*
 *  Mark a queue as closed.  No further IO is permitted.
 *  All blocks are released.
 */
void
qclose(Queue *q)
{
	Block *bfirst;

	if(q == nil)
		return;

	/* mark it */
	ilock(&q->lk);
	q->state |= Qclosed;
	q->state &= ~(Qflow|Qstarve);
	strcpy(q->err, Ehungup);
	bfirst = q->bfirst;
	q->bfirst = 0;
	q->len = 0;
	q->dlen = 0;
	q->noblock = 0;
	iunlock(&q->lk);

	/* free queued blocks */
	freeblist(bfirst);

	/* wake up readers/writers */
	wakeup(&q->rr);
	wakeup(&q->wr);
}

/*
 *  Mark a queue as closed.  Wakeup any readers.  Don't remove queued
 *  blocks.
 */
void
qhangup(Queue *q, char *msg)
{
	/* mark it */
	ilock(&q->lk);
	q->state |= Qclosed;
	if(msg == 0 || *msg == 0)
		strcpy(q->err, Ehungup);
	else
		strncpy(q->err, msg, ERRMAX-1);
	iunlock(&q->lk);

	/* wake up readers/writers */
	wakeup(&q->rr);
	wakeup(&q->wr);
}

/*
 *  return non-zero if the q is hungup
 */
int
qisclosed(Queue *q)
{
	return q->state & Qclosed;
}

/*
 *  mark a queue as no longer hung up
 */
void
qreopen(Queue *q)
{
	ilock(&q->lk);
	q->state &= ~Qclosed;
	q->state |= Qstarve;
	q->eof = 0;
	q->limit = q->inilim;
	iunlock(&q->lk);
}

/*
 *  return bytes queued
 */
int
qlen(Queue *q)
{
	return q->dlen;
}

/*
 * return space remaining before flow control
 */
int
qwindow(Queue *q)
{
	int l;

	l = q->limit - q->len;
	if(l < 0)
		l = 0;
	return l;
}

/*
 *  return true if we can read without blocking
 */
int
qcanread(Queue *q)
{
	return q->bfirst!=0;
}

/*
 *  change queue limit
 */
void
qsetlimit(Queue *q, int limit)
{
	q->limit = limit;
}

/*
 *  set blocking/nonblocking
 */
void
qnoblock(Queue *q, int onoff)
{
	q->noblock = onoff;
}

/*
 *  flush the output queue
 */
void
qflush(Queue *q)
{
	Block *bfirst;

	/* mark it */
	ilock(&q->lk);
	bfirst = q->bfirst;
	q->bfirst = 0;
	q->len = 0;
	q->dlen = 0;
	iunlock(&q->lk);

	/* free queued blocks */
	freeblist(bfirst);

	/* wake up readers/writers */
	wakeup(&q->wr);
}

int
qfull(Queue *q)
{
	return q->state & Qflow;
}

int
qstate(Queue *q)
{
	return q->state;
}