net: add napi_id and hash

Adds a napi_id and a hashing mechanism to lookup a napi by id.
This will be used by subsequent patches to implement low latency
Ethernet device polling.
Based on a code sample by Eric Dumazet.

Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 59 insertions, 0 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 9c18557f93c6..fa007dba6beb 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -129,6 +129,7 @@
 #include <linux/inetdevice.h>
 #include <linux/cpu_rmap.h>
 #include <linux/static_key.h>
+#include <linux/hashtable.h>
 
 #include "net-sysfs.h"
 
@@ -166,6 +167,12 @@ static struct list_head offload_base __read_mostly;
 DEFINE_RWLOCK(dev_base_lock);
 EXPORT_SYMBOL(dev_base_lock);
 
+/* protects napi_hash addition/deletion and napi_gen_id */
+static DEFINE_SPINLOCK(napi_hash_lock);
+
+static unsigned int napi_gen_id;
+static DEFINE_HASHTABLE(napi_hash, 8);
+
 seqcount_t devnet_rename_seq;
 
 static inline void dev_base_seq_inc(struct net *net)
@@ -4136,6 +4143,58 @@ void napi_complete(struct napi_struct *n)
 }
 EXPORT_SYMBOL(napi_complete);
 
+/* must be called under rcu_read_lock(), as we dont take a reference */
+struct napi_struct *napi_by_id(unsigned int napi_id)
+{
+        unsigned int hash = napi_id % HASH_SIZE(napi_hash);
+        struct napi_struct *napi;
+
+        hlist_for_each_entry_rcu(napi, &napi_hash[hash], napi_hash_node)
+                if (napi->napi_id == napi_id)
+                        return napi;
+
+        return NULL;
+}
+EXPORT_SYMBOL_GPL(napi_by_id);
+
+void napi_hash_add(struct napi_struct *napi)
+{
+        if (!test_and_set_bit(NAPI_STATE_HASHED, &napi->state)) {
+
+                spin_lock(&napi_hash_lock);
+
+                /* 0 is not a valid id, we also skip an id that is taken
+                 * we expect both events to be extremely rare
+                 */
+                napi->napi_id = 0;
+                while (!napi->napi_id) {
+                        napi->napi_id = ++napi_gen_id;
+                        if (napi_by_id(napi->napi_id))
+                                napi->napi_id = 0;
+                }
+
+                hlist_add_head_rcu(&napi->napi_hash_node,
+                        &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
+
+                spin_unlock(&napi_hash_lock);
+        }
+}
+EXPORT_SYMBOL_GPL(napi_hash_add);
+
+/* Warning : caller is responsible to make sure rcu grace period
+ * is respected before freeing memory containing @napi
+ */
+void napi_hash_del(struct napi_struct *napi)
+{
+        spin_lock(&napi_hash_lock);
+
+        if (test_and_clear_bit(NAPI_STATE_HASHED, &napi->state))
+                hlist_del_rcu(&napi->napi_hash_node);
+
+        spin_unlock(&napi_hash_lock);
+}
+EXPORT_SYMBOL_GPL(napi_hash_del);
+
 void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
                     int (*poll)(struct napi_struct *, int), int weight)
 {