netmap: refactor netmap_reset

The netmap_reset() function is meant to be called by the driver
when they initialize (or re-initialize) a hardware ring.
However, since the introduction of support for opening (in
netmap mode) a subset of the available rings, netmap_reset()
may be called multiple times on actively used rings, causing
both kring and netmap ring to transition to an inconsistent
state.
This changes improves the situation by resetting all the
indices fields of the kring to 0, as expected after the
reinitialization of a hardware ring.

PR:	    252518
MFC after:  1 week

1 files changed, 20 insertions, 45 deletions

diff --git a/sys/dev/netmap/netmap.c b/sys/dev/netmap/netmap.c
index aa3bb1843ba5..cf85671cae55 100644
--- a/sys/dev/netmap/netmap.c
+++ b/sys/dev/netmap/netmap.c
@@ -4066,75 +4066,50 @@ done:
 
 
 /*
- * netmap_reset() is called by the driver routines when reinitializing
- * a ring. The driver is in charge of locking to protect the kring.
- * If native netmap mode is not set just return NULL.
- * If native netmap mode is set, in particular, we have to set nr_mode to
- * NKR_NETMAP_ON.
+ * Reset function to be called by the driver routines when reinitializing
+ * a hardware ring. The driver is in charge of locking to protect the kring
+ * while this operation is being performed.
+ * This is normally done by calling netmap_disable_all_rings() before
+ * triggering a reset.
+ * If the kring is not in netmap mode, return NULL to inform the caller
+ * that this is the case.
+ * If the kring is in netmap mode, reset the kring indices to 0.
+ * In any case, adjust kring->nr_mode.
  */
 struct netmap_slot *
 netmap_reset(struct netmap_adapter *na, enum txrx tx, u_int n,
 	u_int new_cur)
 {
 	struct netmap_kring *kring;
-	int new_hwofs, lim;
 
 	if (!nm_native_on(na)) {
 		nm_prdis("interface not in native netmap mode");
 		return NULL;	/* nothing to reinitialize */
 	}
 
-	/* XXX note- in the new scheme, we are not guaranteed to be
-	 * under lock (e.g. when called on a device reset).
-	 * In this case, we should set a flag and do not trust too
-	 * much the values. In practice: TODO
-	 * - set a RESET flag somewhere in the kring
-	 * - do the processing in a conservative way
-	 * - let the *sync() fixup at the end.
-	 */
 	if (tx == NR_TX) {
 		if (n >= na->num_tx_rings)
 			return NULL;
 
 		kring = na->tx_rings[n];
 
-		if (kring->nr_pending_mode == NKR_NETMAP_OFF) {
-			kring->nr_mode = NKR_NETMAP_OFF;
-			return NULL;
-		}
-
-		// XXX check whether we should use hwcur or rcur
-		new_hwofs = kring->nr_hwcur - new_cur;
 	} else {
 		if (n >= na->num_rx_rings)
 			return NULL;
 		kring = na->rx_rings[n];
-
-		if (kring->nr_pending_mode == NKR_NETMAP_OFF) {
-			kring->nr_mode = NKR_NETMAP_OFF;
-			return NULL;
-		}
-
-		new_hwofs = kring->nr_hwtail - new_cur;
 	}
-	lim = kring->nkr_num_slots - 1;
-	if (new_hwofs > lim)
-		new_hwofs -= lim + 1;
-
-	/* Always set the new offset value and realign the ring. */
-	if (netmap_debug & NM_DEBUG_ON)
-	    nm_prinf("%s %s%d hwofs %d -> %d, hwtail %d -> %d",
-		na->name,
-		tx == NR_TX ? "TX" : "RX", n,
-		kring->nkr_hwofs, new_hwofs,
-		kring->nr_hwtail,
-		tx == NR_TX ? lim : kring->nr_hwtail);
-	kring->nkr_hwofs = new_hwofs;
-	if (tx == NR_TX) {
-		kring->nr_hwtail = kring->nr_hwcur + lim;
-		if (kring->nr_hwtail > lim)
-			kring->nr_hwtail -= lim + 1;
+	if (kring->nr_pending_mode == NKR_NETMAP_OFF) {
+		kring->nr_mode = NKR_NETMAP_OFF;
+		return NULL;
+	}
+	if (netmap_verbose) {
+	    nm_prinf("%s, was: hc %u h %u c %u ht %u", kring->name,
+	        kring->nr_hwcur, kring->ring->head,
+	        kring->ring->cur, kring->nr_hwtail);
 	}
+	/* For the moment being, nkr_hwofs is not used. */
+	kring->rhead = kring->rcur = kring->nr_hwcur = kring->nkr_hwofs = 0;
+	kring->nr_hwtail = (tx == NR_TX) ? (kring->nkr_num_slots - 1) : 0;
 
 	/*
 	 * Wakeup on the individual and global selwait