net: add netif_set_real_num_queues() for device reconfig

netif_set_real_num_rx_queues() and netif_set_real_num_tx_queues()
can fail which breaks drivers trying to implement reconfiguration
in a way that can't leave the device half-broken. In other words
those functions are incompatible with prepare/commit approach.

Luckily setting real number of queues can fail only if the number
is increased, meaning that if we order operations correctly we
can guarantee ending up with either new config (success), or
the old one (on error).

Provide a helper implementing such logic so that drivers don't
have to duplicate it.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index cd136499ec59edee2952c915eec7c5757f0460be..1b4d4509d04b1e810e900dc62e3e81257a500c48 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3916,6 +3916,8 @@ static inline int netif_set_real_num_rx_queues(struct net_device *dev,
        return 0;
 }
 #endif
+int netif_set_real_num_queues(struct net_device *dev,
+                             unsigned int txq, unsigned int rxq);
 
 static inline struct netdev_rx_queue *
 __netif_get_rx_queue(struct net_device *dev, unsigned int rxq)

diff --git a/net/core/dev.c b/net/core/dev.c
index 4a1401008db97523d044191b9afe33808df30ae8..360cb2f1b1e9ff13951d8043f6e11f2e4e041285 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2973,6 +2973,50 @@ int netif_set_real_num_rx_queues(struct net_device *dev, unsigned int rxq)
 EXPORT_SYMBOL(netif_set_real_num_rx_queues);
 #endif
 
+/**
+ *     netif_set_real_num_queues - set actual number of RX and TX queues used
+ *     @dev: Network device
+ *     @txq: Actual number of TX queues
+ *     @rxq: Actual number of RX queues
+ *
+ *     Set the real number of both TX and RX queues.
+ *     Does nothing if the number of queues is already correct.
+ */
+int netif_set_real_num_queues(struct net_device *dev,
+                             unsigned int txq, unsigned int rxq)
+{
+       unsigned int old_rxq = dev->real_num_rx_queues;
+       int err;
+
+       if (txq < 1 || txq > dev->num_tx_queues ||
+           rxq < 1 || rxq > dev->num_rx_queues)
+               return -EINVAL;
+
+       /* Start from increases, so the error path only does decreases -
+        * decreases can't fail.
+        */
+       if (rxq > dev->real_num_rx_queues) {
+               err = netif_set_real_num_rx_queues(dev, rxq);
+               if (err)
+                       return err;
+       }
+       if (txq > dev->real_num_tx_queues) {
+               err = netif_set_real_num_tx_queues(dev, txq);
+               if (err)
+                       goto undo_rx;
+       }
+       if (rxq < dev->real_num_rx_queues)
+               WARN_ON(netif_set_real_num_rx_queues(dev, rxq));
+       if (txq < dev->real_num_tx_queues)
+               WARN_ON(netif_set_real_num_tx_queues(dev, txq));
+
+       return 0;
+undo_rx:
+       WARN_ON(netif_set_real_num_rx_queues(dev, old_rxq));
+       return err;
+}
+EXPORT_SYMBOL(netif_set_real_num_queues);
+
 /**
  * netif_get_num_default_rss_queues - default number of RSS queues
  *