aoe: update cap on outstanding commands based on config query response

The ATA over Ethernet config query response contains a "buffer count"
field reflecting the AoE target's capacity to buffer incoming AoE
commands.

By taking the current value of this field into accound, we increase
performance throughput or avoid network congestion, when the value
has increased or decreased, respectively.

Signed-off-by: Ed Cashin <ecashin@coraid.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/block/aoe/aoe.h

@@ -122,14 +122,14 @@ struct aoeif {
 
 struct aoetgt {
 	unsigned char addr[6];
-	ushort nframes;
+	ushort nframes;		/* cap on frames to use */
 	struct aoedev *d;			/* parent device I belong to */
 	struct list_head ffree;			/* list of free frames */
 	struct aoeif ifs[NAOEIFS];
 	struct aoeif *ifp;	/* current aoeif in use */
 	ushort nout;
-	ushort maxout;
-	ulong falloc;
+	ushort maxout;		/* current value for max outstanding */
+	ulong falloc;		/* number of allocated frames */
 	ulong lastwadj;		/* last window adjustment */
 	int minbcnt;
 	int wpkts, rpkts;

drivers/block/aoe/aoecmd.c

@@ -1373,7 +1373,11 @@ aoecmd_cfg_rsp(struct sk_buff *skb)
 	spin_lock_irqsave(&d->lock, flags);
 
 	t = gettgt(d, h->src);
-	if (!t) {
+	if (t) {
+		t->nframes = n;
+		if (n < t->maxout)
+			t->maxout = n;
+	} else {
 		t = addtgt(d, h->src, n);
 		if (!t)
 			goto bail;