[PATCH] (3/4) support large number of network devices -- hash ifindex

[Stephen Hemminger <shemminger@xxxxxxxx>]

Add an additional hash chain to keep track of network devices
by index.  This gets used during route manipulation and when
allocating a unique ifindex.

diff -Nru a/include/linux/netdevice.h b/include/linux/netdevice.h
--- a/include/linux/netdevice.h Fri Jan 16 09:27:12 2004
+++ b/include/linux/netdevice.h Fri Jan 16 09:27:12 2004
@@ -377,6 +377,8 @@
        struct list_head        todo_list;
        /* device name hash chain */
        struct hlist_node       name_hlist;
+       /* device index hash chain */
+       struct hlist_node       index_hlist;
 
        /* register/unregister state machine */
        enum { NETREG_UNINITIALIZED=0,
diff -Nru a/net/core/dev.c b/net/core/dev.c
--- a/net/core/dev.c    Fri Jan 16 09:27:12 2004
+++ b/net/core/dev.c    Fri Jan 16 09:27:12 2004
@@ -188,6 +188,7 @@
 
 #define NETDEV_HASHBITS        8
 static struct hlist_head dev_name_head[1<<NETDEV_HASHBITS];
+static struct hlist_head dev_index_head[1<<NETDEV_HASHBITS];
 
 static inline struct hlist_head *dev_name_hash(const char *name)
 {
@@ -196,6 +197,11 @@
        return &dev_name_head[hash & ((1<<NETDEV_HASHBITS)-1)];
 }
 
+static inline struct hlist_head *dev_index_hash(int ifindex)
+{
+       return &dev_index_head[ifindex & ((1<<NETDEV_HASHBITS)-1)];
+}
+
 /*
  *     Our notifier list
  */
@@ -531,12 +537,15 @@
 
 struct net_device *__dev_get_by_index(int ifindex)
 {
-       struct net_device *dev;
+       struct hlist_node *p;
 
-       for (dev = dev_base; dev; dev = dev->next)
+       hlist_for_each(p, dev_index_hash(ifindex)) {
+               struct net_device *dev
+                       = hlist_entry(p, struct net_device, index_hlist);
                if (dev->ifindex == ifindex)
-                       break;
-       return dev;
+                       return dev;
+       }
+       return NULL;
 }
 
 
@@ -2819,6 +2828,7 @@
        *dev_tail = dev;
        dev_tail = &dev->next;
        hlist_add_head(&dev->name_hlist, head);
+       hlist_add_head(&dev->index_hlist, dev_index_hash(dev->ifindex));
        dev_hold(dev);
        dev->reg_state = NETREG_REGISTERING;
        write_unlock_bh(&dev_base_lock);
@@ -3041,6 +3051,7 @@
                if (d == dev) {
                        write_lock_bh(&dev_base_lock);
                        hlist_del(&dev->name_hlist);
+                       hlist_del(&dev->index_hlist);
                        if (dev_tail == &dev->next)
                                dev_tail = dp;
                        *dp = d->next;
@@ -3121,6 +3132,9 @@
 
        for (i = 0; i < ARRAY_SIZE(dev_name_head); i++)
                INIT_HLIST_HEAD(&dev_name_head[i]);
+
+       for (i = 0; i < ARRAY_SIZE(dev_index_head); i++)
+               INIT_HLIST_HEAD(&dev_index_head[i]);
 
        /*
         *      Initialise the packet receive queues.