fill up the qread buffer if possible to conerve syscalls.  free block
lists outside ilock

Reference: /n/patches.lsub.org/patch/qiofull
Date: Sun Oct 28 17:57:50 CET 2012
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/port/qio.c	Thu Apr 12 12:26:29 2012
+++ /sys/src/nix/port/qio.c	Sun Oct 28 16:49:21 2012
@@ -228,7 +228,7 @@
 		} else {
 			/* shouldn't happen but why crash if it does */
 			if(i < 0){
-				print("pullupblock -ve length, from %#p\n",
+				print("pullup negative length packet, called from %#p\n",
 					getcallerpc(&bp));
 				i = 0;
 			}
@@ -577,14 +577,14 @@
 	dowakeup = 0;
 	ilock(q);
 	if(q->len >= q->limit){
-		freeblist(b);
 		iunlock(q);
+		freeblist(b);
 		return -1;
 	}
 	if(q->state & Qclosed){
 		len = BALLOC(b);
-		freeblist(b);
 		iunlock(q);
+		freeblist(b);
 		return len;
 	}
 
@@ -1079,7 +1079,7 @@
 qread(Queue *q, void *vp, int len)
 {
 	Block *b, *first, **l;
-	int blen, n;
+	int n;
 
 	qlock(&q->rlock);
 	if(waserror()){
@@ -1111,23 +1111,17 @@
 			goto again;
 		}
 
-		/*  grab the first block plus as many
-		 *  following blocks as will completely
-		 *  fit in the read.
+		/*
+		 * grab the first block and as many following
+		 * blocks as will partially fit in the read
 		 */
 		n = 0;
 		l = &first;
-		blen = BLEN(b);
 		for(;;) {
 			*l = qremove(q);
 			l = &b->next;
-			n += blen;
-
-			b = q->bfirst;
-			if(b == nil)
-				break;
-			blen = BLEN(b);
-			if(n+blen > len)
+			n += BLEN(b);
+			if(n >= len || (b = q->bfirst) == nil)
 				break;
 		}
 	} else {